mariadb/sql/sql_cache.cc

/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  Description of the query cache:

1. Query_cache object consists of
	- query cache memory pool (cache)
	- queries hash (queries)
	- tables hash (tables)
	- list of blocks ordered as they allocated in memory
(first_block)
	- list of queries block (queries_blocks)
	- list of used tables (tables_blocks)

2. Query cache memory pool (cache) consists of
	- table of steps of memory bins allocation
	- table of free memory bins
	- blocks of memory

3. Memory blocks

Every memory block has the following structure:

+----------------------------------------------------------+
|      Block header (Query_cache_block structure)	   |
+----------------------------------------------------------+
|Table of database table lists (used for queries & tables) |
+----------------------------------------------------------+
|		  Type depended header			   |
|(Query_cache_query, Query_cache_table, Query_cache_result)|
+----------------------------------------------------------+
|			Data ...			   |
+----------------------------------------------------------+

Block header consists of:
- type:
  FREE		Free memory block
  QUERY		Query block
  RESULT	Ready to send result
  RES_CONT	Result's continuation
  RES_BEG	First block of results, that is not yet complete,
		written to cache
  RES_INCOMPLETE  Allocated for results data block
  TABLE		Block with database table description
  INCOMPLETE	The destroyed block
- length of block (length)
- length of data & headers (used)
- physical list links (pnext/pprev) - used for the list of
  blocks ordered as they are allocated in physical memory
- logical list links (next/prev) - used for queries block list, tables block
  list, free memory block lists and list of results block in query
- number of elements in table of database table list (n_tables)

4. Query & results blocks

Query stored in cache consists of following blocks:

more		      more
recent+-------------+ old
<-----|Query block 1|------> double linked list of queries block
 prev |		    | next
      +-------------+
    <-|  table 0    |-> (see "Table of database table lists" description)
    <-|  table 1    |->
      |  ...	    |		+--------------------------+
      +-------------+	 +-------------------------+	   |
NET   |		    |	 |	V		   V	   |
struct|		    |	 +-+------------+   +------------+ |
<-----|query header |----->|Result block|-->|Result block|-+ doublelinked
writer|		    |result|		|<--|		 |   list of results
      +-------------+	   +------------+   +------------+
      |charset	    |	   +------------+   +------------+ no table of dbtables
      |encoding +   |	   |   result	|   |	result	 |
      |query text   |<-----|   header	|   |	header	 |------+
      +-------------+parent|		|   |		 |parent|
	    ^		   +------------+   +------------+	|
	    |		   |result data |   |result data |	|
	    |		   +------------+   +------------+	|
	    +---------------------------------------------------+

First query is registered. During the registration query block is
allocated. This query block is included in query hash and is linked
with appropriate database tables lists (if there is no appropriate
list exists it will be created).

Later when query has performed results is written into the result blocks.
A result block cannot be smaller then QUERY_CACHE_MIN_RESULT_DATA_SIZE.

When new result is written to cache it is appended to the last result
block, if no more  free space left in the last block, new block is
allocated.

5. Table of database table lists.

For quick invalidation of queries all query are linked in lists on used
database tables basis (when table will be changed (insert/delete/...)
this queries will be removed from cache).

Root of such list is table block:

     +------------+	  list of used tables (used while invalidation of
<----|	Table	  |-----> whole database)
 prev|	block	  |next			     +-----------+
     |		  |	  +-----------+      |Query block|
     |		  |	  |Query block|      +-----------+
     +------------+	  +-----------+      | ...	 |
  +->| table 0	  |------>|table 0    |----->| table N	 |---+
  |+-|		  |<------|	      |<-----|		 |<-+|
  || +------------+	  | ...       |      | ...	 |  ||
  || |table header|	  +-----------+      +-----------+  ||
  || +------------+	  | ...       |      | ...	 |  ||
  || |db name +   |	  +-----------+      +-----------+  ||
  || |table name  |					    ||
  || +------------+					    ||
  |+--------------------------------------------------------+|
  +----------------------------------------------------------+

Table block is included into the tables hash (tables).

6. Free blocks, free blocks bins & steps of freeblock bins.

When we just started only one free memory block  existed. All query
cache memory (that will be used for block allocation) were
containing in this block.
When a new block is allocated we find most suitable memory block
(minimal of >= required size). If such a block can not be found, we try
to find max block < required size (if we allocate block for results).
If there is no free memory, oldest query is removed from cache, and then
we try to allocate memory. Last step should be repeated until we find
suitable block or until there is no unlocked query found.

If the block is found and its length more then we need, it should be
split into 2 blocks.
New blocks cannot be smaller then min_allocation_unit_bytes.

When a block becomes free, its neighbor-blocks should be tested and if
there are free blocks among them, they should be joined into one block.

Free memory blocks are stored in bins according to their sizes.
The bins are stored in size-descending order.
These bins are distributed (by size) approximately logarithmically.

First bin (number 0) stores free blocks with
size <= query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2.
It is first (number 0) step.
On the next step distributed (1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
QUERY_CACHE_MEM_BIN_PARTS_MUL bins. This bins allocated in interval from
query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 to
query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 >>
QUERY_CACHE_MEM_BIN_STEP_PWR2
...
On each step interval decreases in 2 power of
QUERY_CACHE_MEM_BIN_STEP_PWR2
times, number of bins (that distributed on this step) increases. If on
the previous step there were N bins distributed , on the current there
would be distributed
(N + QUERY_CACHE_MEM_BIN_PARTS_INC) * QUERY_CACHE_MEM_BIN_PARTS_MUL
bins.
Last distributed bin stores blocks with size near min_allocation_unit
bytes.

For example:
	query_cache_size>>QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2 = 100,
	min_allocation_unit = 17,
	QUERY_CACHE_MEM_BIN_STEP_PWR2 = 1,
	QUERY_CACHE_MEM_BIN_PARTS_INC = 1,
	QUERY_CACHE_MEM_BIN_PARTS_MUL = 1
	(in followed picture showed right (low) bound of bin):

      |       100>>1	 50>>1	      |25>>1|
      |		 |	   |	      |  |  |
      | 100  75 50  41 33 25  21 18 15| 12  | -  bins right (low) bounds

      |\---/\-----/\--------/\--------|---/ |
      |  0     1	2	   3  |     | - steps
       \-----------------------------/ \---/
	bins that we store in cache	this bin showed for example only


Calculation of steps/bins distribution is performed only when query cache
is resized.

When we need to find appropriate bin, first we should find appropriate
step, then we should calculate number of bins that are using data
stored in Query_cache_memory_bin_step structure.

Free memory blocks are sorted in bins in lists with size-ascending order
(more small blocks needed frequently then bigger one).

6. Packing cache.

Query cache packing is divided into two operation:
	- pack_cache
	- join_results

pack_cache moved all blocks to "top" of cache and create one block of free
space at the "bottom":

 before pack_cache    after pack_cache
 +-------------+      +-------------+
 | query 1     |      | query 1     |
 +-------------+      +-------------+
 | table 1     |      | table 1     |
 +-------------+      +-------------+
 | results 1.1 |      | results 1.1 |
 +-------------+      +-------------+
 | free        |      | query 2     |
 +-------------+      +-------------+
 | query 2     |      | table 2     |
 +-------------+ ---> +-------------+
 | table 2     |      | results 1.2 |
 +-------------+      +-------------+
 | results 1.2 |      | results 2   |
 +-------------+      +-------------+
 | free        |      | free        |
 +-------------+      |             |
 | results 2   |      |             |
 +-------------+      |             |
 | free        |      |             |
 +-------------+      +-------------+

pack_cache scan blocks in physical address order and move every non-free
block "higher".

pack_cach remove every free block it finds. The length of the deleted block
is accumulated to the "gap". All non free blocks should be shifted with the
"gap" step.

join_results scans all complete queries. If the results of query are not
stored in the same block, join_results tries to move results so, that they
are stored in one block.

 before join_results  after join_results
 +-------------+      +-------------+
 | query 1     |      | query 1     |
 +-------------+      +-------------+
 | table 1     |      | table 1     |
 +-------------+      +-------------+
 | results 1.1 |      | free        |
 +-------------+      +-------------+
 | query 2     |      | query 2     |
 +-------------+      +-------------+
 | table 2     |      | table 2     |
 +-------------+ ---> +-------------+
 | results 1.2 |      | free        |
 +-------------+      +-------------+
 | results 2   |      | results 2   |
 +-------------+      +-------------+
 | free        |      | results 1   |
 |             |      |             |
 |             |      +-------------+
 |             |      | free        |
 |             |      |             |
 +-------------+      +-------------+

If join_results allocated new block(s) then we need call pack_cache again.
*/

#include "mysql_priv.h"
#include <m_ctype.h>
#include <my_dir.h>
#include <hash.h>
#include "sql_acl.h"
#include "ha_myisammrg.h"
#ifndef MASTER
#include "../srclib/myisammrg/myrg_def.h"
#else
#include "../myisammrg/myrg_def.h"
#endif
#include <assert.h>

#if defined(EXTRA_DEBUG) && !defined(DBUG_OFF)
#define MUTEX_LOCK(M) { DBUG_PRINT("lock", ("mutex lock 0x%lx", (ulong)(M))); \
  pthread_mutex_lock(M);}
#define SEM_LOCK(M) { int val = 0; sem_getvalue (M, &val); \
  DBUG_PRINT("lock", ("sem lock 0x%lx (%d)", (ulong)(M), val)); \
  sem_wait(M); DBUG_PRINT("lock", ("sem lock ok")); }
#define MUTEX_UNLOCK(M) {DBUG_PRINT("lock", ("mutex unlock 0x%lx",\
  (ulong)(M))); pthread_mutex_unlock(M);}
#define SEM_UNLOCK(M) {DBUG_PRINT("lock", ("sem unlock 0x%lx", (ulong)(M))); \
  sem_post(M);	DBUG_PRINT("lock", ("sem unlock ok")); }
#define STRUCT_LOCK(M) {DBUG_PRINT("lock", ("%d struct lock...",__LINE__)); \
  pthread_mutex_lock(M);DBUG_PRINT("lock", ("struct lock OK"));}
#define STRUCT_UNLOCK(M) { \
  DBUG_PRINT("lock", ("%d struct unlock...",__LINE__)); \
  pthread_mutex_unlock(M);DBUG_PRINT("lock", ("struct unlock OK"));}
#define BLOCK_LOCK_WR(B) {DBUG_PRINT("lock", ("%d LOCK_WR 0x%lx",\
  __LINE__,(ulong)(B))); \
  B->query()->lock_writing();}
#define BLOCK_LOCK_RD(B) {DBUG_PRINT("lock", ("%d LOCK_RD 0x%lx",\
  __LINE__,(ulong)(B))); \
  B->query()->lock_reading();}
#define BLOCK_UNLOCK_WR(B) { \
  DBUG_PRINT("lock", ("%d UNLOCK_WR 0x%lx",\
  __LINE__,(ulong)(B)));B->query()->unlock_writing();}
#define BLOCK_UNLOCK_RD(B) { \
  DBUG_PRINT("lock", ("%d UNLOCK_RD 0x%lx",\
  __LINE__,(ulong)(B)));B->query()->unlock_reading();}
#define DUMP(C) DBUG_EXECUTE("qcache", {(C)->queries_dump();(C)->tables_dump();})
#else
#define MUTEX_LOCK(M) pthread_mutex_lock(M)
#define SEM_LOCK(M) sem_wait(M)
#define MUTEX_UNLOCK(M) pthread_mutex_unlock(M)
#define SEM_UNLOCK(M) sem_post(M)
#define STRUCT_LOCK(M) pthread_mutex_lock(M)
#define STRUCT_UNLOCK(M) pthread_mutex_unlock(M)
#define BLOCK_LOCK_WR(B) B->query()->lock_writing()
#define BLOCK_LOCK_RD(B) B->query()->lock_reading()
#define BLOCK_UNLOCK_WR(B) B->query()->unlock_writing()
#define BLOCK_UNLOCK_RD(B) B->query()->unlock_reading()
#define DUMP(C)
#endif

/*****************************************************************************
 Query_cache_block_table method(s)
*****************************************************************************/

inline Query_cache_block * Query_cache_block_table::block()
{
  return (Query_cache_block *)(((byte*)this) -
			       sizeof(Query_cache_block_table)*n -
			       ALIGN_SIZE(sizeof(Query_cache_block)));
};

/*****************************************************************************
   Query_cache_block method(s)
*****************************************************************************/

void Query_cache_block::init(ulong block_length)
{
  DBUG_ENTER("Query_cache_block::init");
  DBUG_PRINT("qcache", ("init block 0x%lx", (ulong) this));
  length = block_length;
  used = 0;
  type = Query_cache_block::FREE;
  n_tables = 0;
  DBUG_VOID_RETURN;
}

void Query_cache_block::destroy()
{
  DBUG_ENTER("Query_cache_block::destroy");
  DBUG_PRINT("qcache", ("destroy block 0x%lx, type %d",
			(ulong) this, type));
  type = INCOMPLETE;
  DBUG_VOID_RETURN;
}

inline uint Query_cache_block::headers_len()
{
  return (ALIGN_SIZE(sizeof(Query_cache_block_table)*n_tables) +
	  ALIGN_SIZE(sizeof(Query_cache_block)));
}

inline gptr Query_cache_block::data(void)
{
  return (gptr)( ((byte*)this) + headers_len() );
}

inline Query_cache_query * Query_cache_block::query()
{
#ifndef DBUG_OFF
  if (type != QUERY)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_query *) data();
}

inline Query_cache_table * Query_cache_block::table()
{
#ifndef DBUG_OFF
  if (type != TABLE)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_table *) data();
}

inline Query_cache_result * Query_cache_block::result()
{
#ifndef DBUG_OFF
  if (type != RESULT && type != RES_CONT && type != RES_BEG &&
      type != RES_INCOMPLETE)
    query_cache.wreck(__LINE__, "incorrect block type");
#endif
  return (Query_cache_result *) data();
}

inline Query_cache_block_table * Query_cache_block::table(TABLE_COUNTER_TYPE n)
{
  return ((Query_cache_block_table *)
	  (((byte*)this)+ALIGN_SIZE(sizeof(Query_cache_block)) +
	   n*sizeof(Query_cache_block_table)));
}


/*****************************************************************************
 *   Query_cache_table method(s)
 *****************************************************************************/

extern "C"
{
byte *query_cache_table_get_key(const byte *record, uint *length,
				my_bool not_used __attribute__((unused)))
{
  Query_cache_block* table_block = (Query_cache_block*) record;
  *length = (table_block->used - table_block->headers_len() -
	     ALIGN_SIZE(sizeof(Query_cache_table)));
  return (((byte *) table_block->data()) +
	  ALIGN_SIZE(sizeof(Query_cache_table)));
}
}

/*****************************************************************************
    Query_cache_query methods
*****************************************************************************/

void Query_cache_query::init_n_lock()
{
  DBUG_ENTER("Query_cache_query::init_n_lock");
  res=0; wri = 0; len = 0;
  sem_init(&lock, 0, 1);
  pthread_mutex_init(&clients_guard,MY_MUTEX_INIT_FAST);
  clients = 0;
  lock_writing();
  DBUG_PRINT("qcache", ("inited & locked query for block 0x%lx",
			((byte*) this)-ALIGN_SIZE(sizeof(Query_cache_block))));
  DBUG_VOID_RETURN;
}


void Query_cache_query::unlock_n_destroy()
{
  DBUG_ENTER("Query_cache_query::unlock_n_destroy");
  /*
    The following call is not needed on system where one can destroy an
    active semaphore
  */
  this->unlock_writing();
  DBUG_PRINT("qcache", ("destroyed & unlocked query for block 0x%lx",
			((byte*)this)-ALIGN_SIZE(sizeof(Query_cache_block))));
  sem_destroy(&lock);
  pthread_mutex_destroy(&clients_guard);
  DBUG_VOID_RETURN;
}


/*
   Following methods work for block read/write locking only in this
   particular case and in interaction with structure_guard_mutex.

   Lock for write prevents any other locking. (exclusive use)
   Lock for read prevents only locking for write.
*/

void Query_cache_query::lock_writing()
{
  SEM_LOCK(&lock);
}


/*
  Needed for finding queries, that we may delete from cache.
  We don't want to wait while block become unlocked. In addition,
  block locking means that query is now used and we don't need to
  remove it.
*/

my_bool Query_cache_query::try_lock_writing()
{
  DBUG_ENTER("Query_cache_block::try_lock_writing");
  if (sem_trywait(&lock)!=0 || clients != 0)
  {
    DBUG_PRINT("qcache", ("can't lock mutex"));
    DBUG_RETURN(0);
  }
  DBUG_PRINT("qcache", ("mutex 'lock' 0x%lx locked", (ulong) &lock));
  DBUG_RETURN(1);
}


void Query_cache_query::lock_reading()
{
  MUTEX_LOCK(&clients_guard);
  if (!clients++)
    SEM_LOCK(&lock);
  MUTEX_UNLOCK(&clients_guard);
}


void Query_cache_query::unlock_writing()
{
  SEM_UNLOCK(&lock);
}


void Query_cache_query::unlock_reading()
{
  MUTEX_LOCK(&clients_guard);
  if (--clients == 0)
    SEM_UNLOCK(&lock);
  MUTEX_UNLOCK(&clients_guard);
}

extern "C"
{
byte *query_cache_query_get_key(const byte *record, uint *length,
				my_bool not_used)
{
  Query_cache_block *query_block = (Query_cache_block*) record;
  *length = (query_block->used - query_block->headers_len() -
	     ALIGN_SIZE(sizeof(Query_cache_query)));
  return (((byte *) query_block->data()) +
	  ALIGN_SIZE(sizeof(Query_cache_query)));
}
}

/*****************************************************************************
 Functions to store things into the query cache
*****************************************************************************/

void query_cache_insert(NET *net, const char *packet, ulong length)
{
  DBUG_ENTER("query_cache_insert");

#ifndef DBUG_OFF
  // Check if we have called query_cache.wreck() (which disables the cache)
  if (query_cache.query_cache_size == 0)
    DBUG_VOID_RETURN;
#endif

  // Quick check on unlocked structure
  if (net->query_cache_query != 0)
  {
    STRUCT_LOCK(&query_cache.structure_guard_mutex);
    Query_cache_block *query_block = ((Query_cache_block*)
				      net->query_cache_query);
    if (query_block)
    {
      Query_cache_query *header = query_block->query();
      Query_cache_block *result = header->result();

      DUMP(&query_cache);
      BLOCK_LOCK_WR(query_block);
      DBUG_PRINT("qcache", ("insert packet %lu bytes long",length));

      /*
	On success STRUCT_UNLOCK(&query_cache.structure_guard_mutex) will be
	done by query_cache.append_result_data if success (if not we need
	query_cache.structure_guard_mutex locked to free query)
      */
      if (!query_cache.append_result_data(&result, length, (gptr) packet,
					  query_block))
      {
	query_cache.refused++;
	DBUG_PRINT("warning", ("Can't append data"));
	header->result(result);
	DBUG_PRINT("qcache", ("free query 0x%lx", (ulong) query_block));
	// The following call will remove the lock on query_block
	query_cache.free_query(query_block);
	// append_result_data no success => we need unlock
	STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
	DBUG_VOID_RETURN;
      }
      header->result(result);
      BLOCK_UNLOCK_WR(query_block);
    }
    else
      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}


void query_cache_abort(NET *net)
{
  DBUG_ENTER("query_cache_abort");

#ifndef DBUG_OFF
  // Check if we have called query_cache.wreck() (which disables the cache)
  if (query_cache.query_cache_size == 0)
    DBUG_VOID_RETURN;
#endif
  if (net->query_cache_query != 0)	// Quick check on unlocked structure
  {
    STRUCT_LOCK(&query_cache.structure_guard_mutex);
    Query_cache_block *query_block = ((Query_cache_block*)
				       net->query_cache_query);
    if (query_block)			// Test if changed by other thread
    {
      DUMP(&query_cache);
      BLOCK_LOCK_WR(query_block);
      // The following call will remove the lock on query_block
      query_cache.free_query(query_block);
      net->query_cache_query=0;
    }
    STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}


void query_cache_end_of_result(NET *net)
{
  DBUG_ENTER("query_cache_end_of_result");

#ifndef DBUG_OFF
  // Check if we have called query_cache.wreck() (which disables the cache)
  if (query_cache.query_cache_size == 0) DBUG_VOID_RETURN;
#endif

  if (net->query_cache_query != 0)	// Quick check on unlocked structure
  {
    STRUCT_LOCK(&query_cache.structure_guard_mutex);
    Query_cache_block *query_block = ((Query_cache_block*)
				      net->query_cache_query);
    if (query_block)
    {
      DUMP(&query_cache);
      BLOCK_LOCK_WR(query_block);
      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);

      Query_cache_query *header = query_block->query();
#ifndef DBUG_OFF
      if (header->result() == 0)
      {
	DBUG_PRINT("error", ("end of data whith no result. query '%s'",
			     header->query()));
	query_cache.wreck(__LINE__, "");
	DBUG_VOID_RETURN;
      }
#endif
      header->found_rows(current_thd->limit_found_rows);
      header->result()->type = Query_cache_block::RESULT;
      net->query_cache_query=0;
      header->writer(0);
      BLOCK_UNLOCK_WR(query_block);
    }
    else
    {
      // Cache was flushed or resized and query was deleted => do nothing
      STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
    }
    net->query_cache_query=0;
  }
  DBUG_VOID_RETURN;
}

void query_cache_invalidate_by_MyISAM_filename(const char *filename)
{
  query_cache.invalidate_by_MyISAM_filename(filename);
}


/*****************************************************************************
   Query_cache methods
*****************************************************************************/

Query_cache::Query_cache(ulong query_cache_limit,
			 ulong min_allocation_unit,
			 ulong min_result_data_size,
			 uint def_query_hash_size ,
			 uint def_table_hash_size)
  :query_cache_size(0),
   query_cache_limit(query_cache_limit),
   queries_in_cache(0), hits(0), inserts(0), refused(0),
   min_allocation_unit(min_allocation_unit),
   min_result_data_size(min_result_data_size),
   def_query_hash_size(def_query_hash_size),
   def_table_hash_size(def_table_hash_size),
   initialized(0)
{
  ulong min_needed=(ALIGN_SIZE(sizeof(Query_cache_block)) +
		    ALIGN_SIZE(sizeof(Query_cache_block_table)) +
		    ALIGN_SIZE(sizeof(Query_cache_query)) + 3);
  set_if_bigger(min_allocation_unit,min_needed);
  this->min_allocation_unit = min_allocation_unit;
  set_if_bigger(this->min_result_data_size,min_allocation_unit);
}


ulong Query_cache::resize(ulong query_cache_size)
{
  /*
     TODO:
     When will be realized pack() optimize case when
     query_cache_size < this->query_cache_size

     Try to copy old cache in new memory
  */
  DBUG_ENTER("Query_cache::resize");
  DBUG_PRINT("qcache", ("from %lu to %lu",this->query_cache_size,
		      query_cache_size));
  free_cache(0);
  this->query_cache_size=query_cache_size;
  DBUG_RETURN(init_cache());
}


void Query_cache::store_query(THD *thd, TABLE_LIST *tables_used)
{
  /*
    TODO:
    Maybe better convert keywords to upper case when query stored/compared.
    (Not important at this stage)
  */
  TABLE_COUNTER_TYPE tables;
  DBUG_ENTER("Query_cache::store_query");
  if (query_cache_size == 0)
    DBUG_VOID_RETURN;

  if ((tables = is_cacheable(thd, thd->query_length,
			     thd->query, &thd->lex, tables_used)))
  {
    NET *net = &thd->net;
    byte flags = (thd->client_capabilities & CLIENT_LONG_FLAG ? 0x80 : 0);
    STRUCT_LOCK(&structure_guard_mutex);

    if (query_cache_size == 0)
      DBUG_VOID_RETURN;
    DUMP(this);

    /*
       Prepare flags:
       most significant bit - CLIENT_LONG_FLAG,
       other - charset number (0 no charset convertion)
    */
    if (thd->convert_set != 0)
    {
      flags|= (byte) thd->convert_set->number();
      DBUG_ASSERT(thd->convert_set->number() < 128);
    }

    /* Check if another thread is processing the same query? */
    thd->query[thd->query_length] = (char) flags;
    Query_cache_block *competitor = (Query_cache_block *)
      hash_search(&queries, thd->query, thd->query_length+1);
    DBUG_PRINT("qcache", ("competitor 0x%lx, flags %x", (ulong) competitor,
			flags));
    if (competitor == 0)
    {
      /* Query is not in cache and no one is working with it; Store it */
      thd->query[thd->query_length] = (char) flags;
      Query_cache_block *query_block;
      query_block= write_block_data(thd->query_length+1,
				    (gptr) thd->query,
				    ALIGN_SIZE(sizeof(Query_cache_query)),
				    Query_cache_block::QUERY, tables, 1);
      if (query_block != 0)
      {
	DBUG_PRINT("qcache", ("query block 0x%lx allocated, %lu",
			    (ulong) query_block, query_block->used));

	Query_cache_query *header = query_block->query();
	header->init_n_lock();
	if (hash_insert(&queries, (byte*) query_block))
	{
	  refused++;
	  DBUG_PRINT("qcache", ("insertion in query hash"));
	  header->unlock_n_destroy();
	  free_memory_block(query_block);
	  STRUCT_UNLOCK(&structure_guard_mutex);
	  goto end;
	}
	if (!register_all_tables(query_block, tables_used, tables))
	{
	  refused++;
	  DBUG_PRINT("warning", ("tables list including failed"));
	  hash_delete(&queries, (char *) query_block);
	  header->unlock_n_destroy();
	  free_memory_block(query_block);
	  STRUCT_UNLOCK(&structure_guard_mutex);
	  DBUG_VOID_RETURN;
	}
	double_linked_list_simple_include(query_block, &queries_blocks);
	inserts++;
	queries_in_cache++;
	STRUCT_UNLOCK(&structure_guard_mutex);

	net->query_cache_query = (gptr) query_block;
	header->writer(net);
	// init_n_lock make query block locked
	BLOCK_UNLOCK_WR(query_block);
      }
      else
      {
	// We have not enough memory to store query => do nothing
	refused++;
	STRUCT_UNLOCK(&structure_guard_mutex);
	DBUG_PRINT("warning", ("Can't allocate query"));
      }
    }
    else
    {
      // Another thread is processing the same query => do nothing
      refused++;
      STRUCT_UNLOCK(&structure_guard_mutex);
      DBUG_PRINT("qcache", ("Another thread process same query"));
    }
  }
  else
    statistic_increment(refused, &structure_guard_mutex);

end:
  thd->query[thd->query_length]= 0;		// Restore end null
  DBUG_VOID_RETURN;
}


my_bool
Query_cache::send_result_to_client(THD *thd, char *sql, uint query_length)
{
  Query_cache_query *query;
  Query_cache_block *first_result_block, *result_block;
  Query_cache_block_table *block_table, *block_table_end;
  byte flags;
  DBUG_ENTER("Query_cache::send_result_to_client");

  if (query_cache_size == 0 ||
      /*
	it is not possible to check has_transactions() function of handler
	because tables not opened yet
      */
      (thd->options & (OPTION_NOT_AUTO_COMMIT | OPTION_BEGIN)) ||
      thd->query_cache_type == 0)

  {
    DBUG_PRINT("qcache", ("query cache disabled on not in autocommit mode"));
    goto err;
  }
  /*
    We can't cache the query if we are using a temporary table because
    we don't know if the query is using a temporary table.

    TODO:  We could parse the query and then check if the query used
	   a temporary table.
  */
  if (thd->temporary_tables != 0 || !thd->safe_to_cache_query)
  {
    DBUG_PRINT("qcache", ("SELECT is non-cacheable"));
    goto err;
  }

  /* Test if the query is a SELECT */
  while (*sql == ' ' || *sql == '\t')
  {
    sql++;
    query_length--;
  }
  if (toupper(sql[0]) != 'S' || toupper(sql[1]) != 'E' ||
      toupper(sql[2]) !='L')
  {
    DBUG_PRINT("qcache", ("The statement is not a SELECT; Not cached"));
    goto err;
  }

  STRUCT_LOCK(&structure_guard_mutex);
  if (query_cache_size == 0)
  {
    DBUG_PRINT("qcache", ("query cache disabled and not in autocommit mode"));
    STRUCT_UNLOCK(&structure_guard_mutex);
    goto err;
  }
  DBUG_PRINT("qcache", (" sql %u '%s'", query_length, sql));
  Query_cache_block *query_block;

  /*
     prepare flags:
     Most significant bit - CLIENT_LONG_FLAG,
     Other - charset number (0 no charset convertion)
  */
  flags = (thd->client_capabilities & CLIENT_LONG_FLAG ? 0x80 : 0);
  if (thd->convert_set != 0)
  {
    flags |= (byte) thd->convert_set->number();
    DBUG_ASSERT(thd->convert_set->number() < 128);
  }

  sql[query_length] = (char) flags;
  query_block = (Query_cache_block *)  hash_search(&queries, sql,
						   query_length+1);
  sql[query_length] = '\0';

  /* Quick abort on unlocked data */
  if (query_block == 0 ||
      query_block->query()->result() == 0 ||
      query_block->query()->result()->type != Query_cache_block::RESULT)
  {
    STRUCT_UNLOCK(&structure_guard_mutex);
    DBUG_PRINT("qcache", ("No query in query hash or no results"));
    goto err;
  }
  DBUG_PRINT("qcache", ("Query in query hash 0x%lx", (ulong)query_block));

  /* Now lock and test that nothing changed while blocks was unlocked */
  BLOCK_LOCK_RD(query_block);

  query = query_block->query();
  result_block= first_result_block= query->result();

  if (result_block == 0 || result_block->type != Query_cache_block::RESULT)
  {
    /* The query is probably yet processed */
    DBUG_PRINT("qcache", ("query found, but no data or data incomplete"));
    BLOCK_UNLOCK_RD(query_block);
    goto err;
  }
  DBUG_PRINT("qcache", ("Query have result 0x%lx", (ulong) query));

  // Check access;
  block_table= query_block->table(0);
  block_table_end= block_table+query_block->n_tables;
  for ( ; block_table != block_table_end; block_table++)
  {
    TABLE_LIST table_list;
    bzero((char*) &table_list,sizeof(table_list));

    Query_cache_table *table = block_table->parent;
    table_list.db = table->db();
    table_list.name = table_list.real_name = table->table();
    if (check_table_access(thd,SELECT_ACL,&table_list))
    {
      DBUG_PRINT("qcache",
		 ("probably no SELECT access to %s.%s =>  return to normal processing",
		  table_list.db, table_list.name));
      BLOCK_UNLOCK_RD(query_block);
      STRUCT_UNLOCK(&structure_guard_mutex);
      goto err;
    }
  }
  move_to_query_list_end(query_block);
  hits++;
  STRUCT_UNLOCK(&structure_guard_mutex);

  /*
    Send cached result to client
  */
  do
  {
    DBUG_PRINT("qcache", ("Results  (len %lu, used %lu, headers %lu)",
			result_block->length, result_block->used,
			result_block->headers_len()+
			ALIGN_SIZE(sizeof(Query_cache_result))));

    Query_cache_result *result = result_block->result();
    if (net_real_write(&thd->net, result->data(),
		       result_block->used -
		       result_block->headers_len() -
		       ALIGN_SIZE(sizeof(Query_cache_result))))
      break;					// Client aborted
    result_block = result_block->next;
  } while (result_block != first_result_block);

  thd->limit_found_rows = query->found_rows();

  BLOCK_UNLOCK_RD(query_block);
  DBUG_RETURN(0);

err:
  DBUG_RETURN(1);
}

/*
  Remove all cached queries that uses any of the tables in the list
*/

void Query_cache::invalidate(TABLE_LIST *tables_used)
{
  DBUG_ENTER("Query_cache::invalidate (table list)");
  if (query_cache_size > 0)
  {
    STRUCT_LOCK(&structure_guard_mutex);
    if (query_cache_size > 0)
    {
      DUMP(this);
      for ( ; tables_used; tables_used=tables_used->next)
	invalidate_table(tables_used);
    }
    STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}

/*
  Remove all cached queries that uses the given table
*/

void Query_cache::invalidate(TABLE *table)
{
  DBUG_ENTER("Query_cache::invalidate (table)");
  if (query_cache_size > 0)
  {
    STRUCT_LOCK(&structure_guard_mutex);
    if (query_cache_size > 0)
      invalidate_table(table);
    STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}


/*
  Remove all cached queries that uses the given table type.
  TODO: This is currently used to invalidate InnoDB tables on commit.
	We should remove this function and only invalidate tables
	used in the transaction.
*/

void Query_cache::invalidate(Query_cache_table::query_cache_table_type type)
{
  DBUG_ENTER("Query_cache::invalidate (type)");
  if (query_cache_size > 0)
  {
    STRUCT_LOCK(&structure_guard_mutex);
    DUMP(this);
    if (query_cache_size > 0 && tables_blocks[type] != 0)
    {
      Query_cache_block *table_block = tables_blocks[type];
      do
      {
	/* Store next block address defore deleting the current block */
	Query_cache_block *next = table_block->next;
	invalidate_table(table_block);
#ifdef TO_BE_DELETED
	if (next == table_block)		// End of list
	  break;
#endif
	table_block = next;
      } while (table_block != tables_blocks[type]);
    }
    STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}


/*
  Remove all cached queries that uses the given database
*/

void Query_cache::invalidate(char *db)
{
  DBUG_ENTER("Query_cache::invalidate (db)");
  if (query_cache_size > 0)
  {
    STRUCT_LOCK(&structure_guard_mutex);
    if (query_cache_size > 0)
    {
      DUMP(this);
      int i = 0;
      for(; i < (int) Query_cache_table::TYPES_NUMBER; i++)
      {
	if (tables_blocks[i] != 0) // Cache not empty
	{
	  Query_cache_block *table_block = tables_blocks[i];
	  do
	  {
	    /*
	      Store next block address defore deletetion of current block
	    */
	    Query_cache_block *next = table_block->next;

	    invalidate_table_in_db(table_block, db);
#ifdef TO_BE_DELETED
	    if (table_block == next)
	      break;
#endif
	    table_block = next;
	  } while (table_block != tables_blocks[i]);
	}
      }
    }
    STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}


void Query_cache::invalidate_by_MyISAM_filename(const char *filename)
{
  DBUG_ENTER("Query_cache::invalidate_by_MyISAM_filename");
  if (query_cache_size > 0)
  {
    /* Calculate the key outside the lock to make the lock shorter */
    char key[MAX_DBKEY_LENGTH];
    uint key_length= filename_2_table_key(key, filename);
    STRUCT_LOCK(&structure_guard_mutex);
    if (query_cache_size > 0)			// Safety if cache removed
    {
      Query_cache_block *table_block;
      if ((table_block = (Query_cache_block*) hash_search(&tables, key,
							  key_length)))
	invalidate_table(table_block);
    }
    STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}

  /* Remove all queries from cache */

void Query_cache::flush()
{
  DBUG_ENTER("Query_cache::flush");
  STRUCT_LOCK(&structure_guard_mutex);
  if (query_cache_size > 0)
  {
    DUMP(this);
    flush_cache();
    DUMP(this);
  }
  STRUCT_UNLOCK(&structure_guard_mutex);
  DBUG_VOID_RETURN;
}

  /* Join result in cache in 1 block (if result length > join_limit) */

void Query_cache::pack(ulong join_limit, uint iteration_limit)
{
  DBUG_ENTER("Query_cache::pack");
  uint i = 0;
  do
  {
    pack_cache();
  } while ((++i < iteration_limit) && join_results(join_limit));
  DBUG_VOID_RETURN;
}


void Query_cache::destroy()
{
  DBUG_ENTER("Query_cache::destroy");
  free_cache(1);
  pthread_mutex_destroy(&structure_guard_mutex);
  initialized = 0;
  DBUG_VOID_RETURN;
}


/*****************************************************************************
  init/destroy
*****************************************************************************/

void Query_cache::init()
{
  DBUG_ENTER("Query_cache::init");
  pthread_mutex_init(&structure_guard_mutex,MY_MUTEX_INIT_FAST);
  initialized = 1;
  DBUG_VOID_RETURN;
}


ulong Query_cache::init_cache()
{
  uint mem_bin_count, num, step;
  ulong mem_bin_size, prev_size, inc;
  ulong additional_data_size, max_mem_bin_size, approx_additional_data_size;

  DBUG_ENTER("Query_cache::init_cache");
  if (!initialized)
    init();
  approx_additional_data_size = (sizeof(Query_cache) +
				 sizeof(gptr)*(def_query_hash_size+
					       def_query_hash_size));
  if (query_cache_size < approx_additional_data_size)
    goto err;

  query_cache_size -= approx_additional_data_size;

  /*
    Count memory bins number.
    Check section 6. in start comment for the used algorithm.
  */

  max_mem_bin_size = query_cache_size >> QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2;
  mem_bin_count = (uint)  ((1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
			   QUERY_CACHE_MEM_BIN_PARTS_MUL);
  mem_bin_num = 1;
  mem_bin_steps = 1;
  mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
  prev_size = 0;
  while (mem_bin_size > min_allocation_unit)
  {
    mem_bin_num += mem_bin_count;
    prev_size = mem_bin_size;
    mem_bin_size >>= QUERY_CACHE_MEM_BIN_STEP_PWR2;
    mem_bin_steps++;
    mem_bin_count += QUERY_CACHE_MEM_BIN_PARTS_INC;
    mem_bin_count = (uint) (mem_bin_count * QUERY_CACHE_MEM_BIN_PARTS_MUL);

    // Prevent too small bins spacing
    if (mem_bin_count > (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2))
      mem_bin_count= (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2);
  }
  inc = (prev_size - mem_bin_size) / mem_bin_count;
  mem_bin_num += (mem_bin_count - (min_allocation_unit - mem_bin_size)/inc);
  mem_bin_steps++;
  additional_data_size = ((mem_bin_num+1) *
			  ALIGN_SIZE(sizeof(Query_cache_memory_bin))+
			  (mem_bin_steps *
			   ALIGN_SIZE(sizeof(Query_cache_memory_bin_step))));

  if (query_cache_size < additional_data_size)
    goto err;
  query_cache_size -= additional_data_size;

  STRUCT_LOCK(&structure_guard_mutex);
  if (query_cache_size	<= min_allocation_unit)
  {
    DBUG_PRINT("qcache",
	       (" query_cache_size <= min_allocation_unit => cache disabled"));
    STRUCT_UNLOCK(&structure_guard_mutex);
    goto err;
  }

  if (!(cache = (byte *)
	 my_malloc_lock(query_cache_size+additional_data_size, MYF(0))))
  {
    STRUCT_UNLOCK(&structure_guard_mutex);
    goto err;
  }

  DBUG_PRINT("qcache", ("cache length %lu, min unit %lu, %u bins",
		      query_cache_size, min_allocation_unit, mem_bin_num));

  steps = (Query_cache_memory_bin_step *) cache;
  bins = ((Query_cache_memory_bin *)
	  (cache + mem_bin_steps *
	   ALIGN_SIZE(sizeof(Query_cache_memory_bin_step))));

  first_block = (Query_cache_block *) (cache + additional_data_size);
  first_block->init(query_cache_size);
  first_block->pnext=first_block->pprev=first_block;
  first_block->next=first_block->prev=first_block;

  /* Prepare bins */

  bins[0].init(max_mem_bin_size);
  steps[0].init(max_mem_bin_size,0,0);
  mem_bin_count = (uint) ((1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
			  QUERY_CACHE_MEM_BIN_PARTS_MUL);
  num= step= 1;
  mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
  while (mem_bin_size > min_allocation_unit)
  {
    ulong incr = (steps[step-1].size - mem_bin_size) / mem_bin_count;
    unsigned long size = mem_bin_size;
    for (uint i= mem_bin_count; i > 0; i--)
    {
      bins[num+i-1].init(size);
      size += incr;
    }
    num += mem_bin_count;
    steps[step].init(mem_bin_size, num-1, incr);
    mem_bin_size >>= QUERY_CACHE_MEM_BIN_STEP_PWR2;
    step++;
    mem_bin_count += QUERY_CACHE_MEM_BIN_PARTS_INC;
    mem_bin_count = (uint) (mem_bin_count * QUERY_CACHE_MEM_BIN_PARTS_MUL);
    if (mem_bin_count > (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2))
      mem_bin_count=(mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2);
  }
  inc = (steps[step-1].size - mem_bin_size) / mem_bin_count;

  /*
    num + mem_bin_count > mem_bin_num, but index never be > mem_bin_num
    because block with size < min_allocated_unit never will be requested
  */

  steps[step].init(mem_bin_size, num + mem_bin_count - 1, inc);
  {
    uint skiped = (min_allocation_unit - mem_bin_size)/inc;
    ulong size = mem_bin_size + inc*skiped;
    uint i = mem_bin_count - skiped;
    while (i-- > 0)
    {
      bins[num+i].init(size);
      size += inc;
    }
  }
  bins[mem_bin_num].number= 1;			// For easy end test
  free_memory= 0;
  insert_into_free_memory_list(first_block);

  DUMP(this);

  VOID(hash_init(&queries,def_query_hash_size, 0, 0,
		 query_cache_query_get_key, 0, 0));
  VOID(hash_init(&tables,def_table_hash_size, 0, 0,
		 query_cache_table_get_key, 0, 0));

  queries_in_cache = 0;
  queries_blocks = 0;
  STRUCT_UNLOCK(&structure_guard_mutex);
  DBUG_RETURN(query_cache_size +
	      additional_data_size + approx_additional_data_size);

err:
  make_disabled();
  DBUG_RETURN(0);
}


/* Disable the use of the query cache */

void Query_cache::make_disabled()
{
  DBUG_ENTER("Query_cache::make_disabled");
  query_cache_size= 0;
  free_memory= 0;
  bins= 0;
  steps= 0;
  cache= 0;
  mem_bin_num= mem_bin_steps= 0;
  queries_in_cache= 0;
  first_block= 0;
  DBUG_VOID_RETURN;
}


void Query_cache::free_cache(my_bool destruction)
{
  DBUG_ENTER("Query_cache::free_cache");
  if (query_cache_size > 0)
  {
    if (!destruction)
      STRUCT_LOCK(&structure_guard_mutex);

    flush_cache();
#ifndef DBUG_OFF
    if (bins[0].free_blocks == 0)
    {
      wreck(__LINE__,"no free memory found in (bins[0].free_blocks");
    }
#endif

    /* Becasue we did a flush, all cache memory must be in one this block */
    bins[0].free_blocks->destroy();
    DBUG_PRINT("qcache", ("free memory %lu (should be %lu)",
			  free_memory , query_cache_size));
    my_free((gptr) cache, MYF(MY_ALLOW_ZERO_PTR));
    make_disabled();
    hash_free(&queries);
    hash_free(&tables);
    if (!destruction)
      STRUCT_UNLOCK(&structure_guard_mutex);
  }
  DBUG_VOID_RETURN;
}

/*****************************************************************************
 Free block data
*****************************************************************************/

/*
  The following assumes we have a lock on the cache
*/

void Query_cache::flush_cache()
{
  while (queries_blocks != 0)
  {
    BLOCK_LOCK_WR(queries_blocks);
    free_query(queries_blocks);
  }
}

/*
  Free oldest query that is not in use by another thread.
  Returns 1 if we couldn't remove anything
*/

my_bool Query_cache::free_old_query()
{
  DBUG_ENTER("Query_cache::free_old_query");
  if (queries_blocks)
  {
    /*
      try_lock_writing used to prevent client because here lock
      sequence is breached.
      Also we don't need remove locked queries at this point.
    */
    Query_cache_block *query_block = 0;
    if (queries_blocks != 0)
    {
      Query_cache_block *block = queries_blocks;
      /* Search until we find first query that we can remove */
      do
      {
	Query_cache_query *header = block->query();
	if (header->result() != 0 &&
	    header->result()->type == Query_cache_block::RESULT &&
	    block->query()->try_lock_writing())
	{
	  query_block = block;
	  break;
	}
      } while ((block=block->next) != queries_blocks );
    }

    if (query_block != 0)
    {
      free_query(query_block);
      DBUG_RETURN(0);
    }
  }
  DBUG_RETURN(1);				// Nothing to remove
}

/*
  Free query from query cache.
  query_block must be locked for writing.
  This function will remove (and destroy) the lock for the query.
*/

void Query_cache::free_query(Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::free_query");
  DBUG_PRINT("qcache", ("free query 0x%lx %lu bytes result",
		      (ulong) query_block,
		      query_block->query()->length() ));

  queries_in_cache--;
  hash_delete(&queries,(byte *) query_block);

  Query_cache_query *query = query_block->query();

  if (query->writer() != 0)
  {
    /* Tell MySQL that this query should not be cached anymore */
    query->writer()->query_cache_query = 0;
    query->writer(0);
  }
  double_linked_list_exclude(query_block, &queries_blocks);
  Query_cache_block_table *table=query_block->table(0);

  for (TABLE_COUNTER_TYPE i=0; i < query_block->n_tables; i++)
    unlink_table(table++);
  Query_cache_block *result_block = query->result();

  /*
    The following is true when query destruction was called and no results
    in query . (query just registered and then abort/pack/flush called)
  */
  if (result_block != 0)
  {
    Query_cache_block *block = result_block;
    do
    {
      Query_cache_block *current = block;
      block = block->next;
      free_memory_block(current);
    } while (block != result_block);
  }

  query->unlock_n_destroy();
  free_memory_block(query_block);

  DBUG_VOID_RETURN;
}

/*****************************************************************************
 Query data creation
*****************************************************************************/

Query_cache_block *
Query_cache::write_block_data(ulong data_len, gptr data,
			      ulong header_len,
			      Query_cache_block::block_type type,
			      TABLE_COUNTER_TYPE ntab,
			      my_bool under_guard)
{
  ulong all_headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
			   ALIGN_SIZE(ntab*sizeof(Query_cache_block_table)) +
			   header_len);
  ulong len = data_len + all_headers_len;
  DBUG_ENTER("Query_cache::write_block_data");
  DBUG_PRINT("qcache", ("data: %ld, header: %ld, all header: %ld",
		      data_len, header_len, all_headers_len));
  Query_cache_block *block = allocate_block(max(len, min_allocation_unit),
					    1, 0, under_guard);
  if (block != 0)
  {
    block->type = type;
    block->n_tables = ntab;
    block->used = len;

    memcpy((void*) (((byte *) block)+ all_headers_len),
	   (void*) data, data_len);
  }
  DBUG_RETURN(block);
}


/*
  On success STRUCT_UNLOCK(&query_cache.structure_guard_mutex) will be done.
*/

my_bool
Query_cache::append_result_data(Query_cache_block **current_block,
				ulong data_len, gptr data,
				Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::append_result_data");
  DBUG_PRINT("qcache", ("append %lu bytes to 0x%lx query",
		      data_len, query_block));

  if (query_block->query()->add(data_len) > query_cache_limit)
  {
    DBUG_PRINT("qcache", ("size limit reached %lu > %lu",
			query_block->query()->length(),
			query_cache_limit));
    *current_block=0;				// Mark error
    DBUG_RETURN(0);
  }
  if (*current_block == 0)
  {
    DBUG_PRINT("qcache", ("allocated first result data block %lu", data_len));
    /*
      STRUCT_UNLOCK(&structure_guard_mutex) Will be done by
      write_result_data if success;
    */
    DBUG_RETURN(write_result_data(current_block, data_len, data, query_block,
				  Query_cache_block::RES_BEG));
  }
  Query_cache_block *last_block = (*current_block)->prev;

  DBUG_PRINT("qcache", ("lastblock 0x%lx len %lu used %lu",
		      (ulong) last_block, last_block->length,
		      last_block->used));
  my_bool success = 1;
  ulong last_block_free_space= last_block->length - last_block->used;

  /*
    We will first allocate and write the 'tail' of data, that doesn't fit
    in the 'last_block'.  Only if this succeeds, we will fill the last_block.
    This saves us a memcpy if the query doesn't fit in the query cache.
  */

  // Try join blocks if physically next block is free...
  if (last_block_free_space < data_len &&
      append_next_free_block(last_block,
			     max(data_len - last_block_free_space,
				 QUERY_CACHE_MIN_RESULT_DATA_SIZE)))
    last_block_free_space = last_block->length - last_block->used;
  // If no space in last block (even after join) allocate new block
  if (last_block_free_space < data_len)
  {
    // TODO: Try get memory from next free block (if exist) (is it needed?)
    DBUG_PRINT("qcache", ("allocate new block for %lu bytes",
			data_len-last_block_free_space));
    Query_cache_block *new_block = 0;
    /*
      On success STRUCT_UNLOCK(&structure_guard_mutex) will be done
      by the next call
    */
    success = write_result_data(&new_block, data_len-last_block_free_space,
				(gptr)(((byte*)data)+last_block_free_space),
				query_block,
				Query_cache_block::RES_CONT);
    /*
       new_block may be not 0 even !success (if write_result_data
       allocate small block but failed allocate continue
    */
    if (new_block != 0)
      double_linked_list_join(last_block, new_block);
  }
  else
  {
    // It is success (nobody can prevent us write data)
    STRUCT_UNLOCK(&structure_guard_mutex);
  }

  // Now finally write data to the last block
  if (success && last_block_free_space > 0)
  {
    ulong to_copy = min(data_len,last_block_free_space);
    DBUG_PRINT("qcache", ("use free space %lub at block 0x%lx to copy %lub",
			last_block_free_space, (ulong)last_block, to_copy));
    memcpy((void*) (((byte*) last_block) + last_block->used), (void*) data,
	   to_copy);
    last_block->used+=to_copy;
  }
  DBUG_RETURN(success);
}


my_bool Query_cache::write_result_data(Query_cache_block **result_block,
				       ulong data_len, gptr data,
				       Query_cache_block *query_block,
				       Query_cache_block::block_type type)
{
  DBUG_ENTER("Query_cache::write_result_data");
  DBUG_PRINT("qcache", ("data_len %lu",data_len));

  /*
    Reserve block(s) for filling
    During data allocation we must have structure_guard_mutex locked.
    As data copy is not a fast operation, it's better if we don't have
    structure_guard_mutex locked during data coping.
    Thus we first allocate space and lock query, then unlock
    structure_guard_mutex and copy data.
  */

  my_bool success = allocate_data_chain(result_block, data_len, query_block);
  if (success)
  {
    // It is success (nobody can prevent us write data)
    STRUCT_UNLOCK(&structure_guard_mutex);
    byte *rest = (byte*) data;
    Query_cache_block *block = *result_block;
    uint headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
			ALIGN_SIZE(sizeof(Query_cache_result)));
    // Now fill list of blocks that created by allocate_data_chain
    do
    {
      block->type = type;
      ulong length = block->used - headers_len;
      DBUG_PRINT("qcache", ("write %lu byte in block 0x%lx",length,
			  (ulong)block));
      memcpy((void*)(((byte*) block)+headers_len), (void*) rest, length);
      rest += length;
      block = block->next;
      type = Query_cache_block::RES_CONT;
    } while (block != *result_block);
  }
  else
  {
    if (*result_block != 0)
    {
      // Destroy list of blocks that was created & locked by lock_result_data
      Query_cache_block *block = *result_block;
      do
      {
	Query_cache_block *current = block;
	block = block->next;
	free_memory_block(current);
      } while (block != *result_block);
      *result_block = 0;
      /*
	It is not success => not unlock structure_guard_mutex (we need it to
	free query)
      */
    }
  }
  DBUG_PRINT("qcache", ("success %d", (int) success));
  DBUG_RETURN(success);
}

/*
  Allocate one or more blocks to hold data
*/

my_bool Query_cache::allocate_data_chain(Query_cache_block **result_block,
					 ulong data_len,
					 Query_cache_block *query_block)
{
  ulong all_headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
			   ALIGN_SIZE(sizeof(Query_cache_result)));
  ulong len = data_len + all_headers_len;
  DBUG_ENTER("Query_cache::allocate_data_chain");
  DBUG_PRINT("qcache", ("data_len %lu, all_headers_len %lu",
		      data_len, all_headers_len));

  *result_block = allocate_block(max(min_result_data_size,len),
				 min_result_data_size == 0,
				 all_headers_len + min_result_data_size,
				 1);
  my_bool success = (*result_block != 0);
  if (success)
  {
    Query_cache_block *new_block= *result_block;
    new_block->n_tables = 0;
    new_block->used = 0;
    new_block->type = Query_cache_block::RES_INCOMPLETE;
    new_block->next = new_block->prev = new_block;
    Query_cache_result *header = new_block->result();
    header->parent(query_block);

    if (new_block->length < len)
    {
      /*
	We got less memory then we need (no big memory blocks) =>
	Continue to allocated more blocks until we got everything we need.
      */
      Query_cache_block *next_block;
      if ((success = allocate_data_chain(&next_block,
					 len - new_block->length,
					 query_block)))
	double_linked_list_join(new_block, next_block);
    }
    if (success)
    {
      new_block->used = min(len, new_block->length);

      DBUG_PRINT("qcache", ("Block len %lu used %lu",
			  new_block->length, new_block->used));
    }
    else
      DBUG_PRINT("warning", ("Can't allocate block for continue"));
  }
  else
    DBUG_PRINT("warning", ("Can't allocate block for results"));
  DBUG_RETURN(success);
}

/*****************************************************************************
  Tables management
*****************************************************************************/

/*
  Invalidate the first table in the table_list
*/

void Query_cache::invalidate_table(TABLE_LIST *table_list)
{
  if (table_list->table != 0)
    invalidate_table(table_list->table);	// Table is open
  else
  {
    char key[MAX_DBKEY_LENGTH];
    uint key_length;
    Query_cache_block *table_block;
    key_length=(uint) (strmov(strmov(key,table_list->db)+1,
			      table_list->real_name) -key)+ 1;

    // We don't store temporary tables => no key_length+=4 ...
    if ((table_block = (Query_cache_block*)
	 hash_search(&tables,key,key_length)))
      invalidate_table(table_block);
  }
}

void Query_cache::invalidate_table(TABLE *table)
{
  Query_cache_block *table_block;
  if ((table_block = ((Query_cache_block*)
		      hash_search(&tables, table->table_cache_key,
				  table->key_length))))
    invalidate_table(table_block);
}

void Query_cache::invalidate_table_in_db(Query_cache_block *table_block,
					 char *db)
{
  /*
    table key consist of data_base_name + '\0' + table_name +'\0'...
    => we may use strcmp to compare database names.
  */
  if (strcmp(db, (char*)(table_block->table()->db())) == 0)
    invalidate_table(table_block);
}


void Query_cache::invalidate_table(Query_cache_block *table_block)
{
  Query_cache_block_table *list_root =	table_block->table(0);
  while (list_root->next != list_root)
  {
    Query_cache_block *query_block = list_root->next->block();
    BLOCK_LOCK_WR(query_block);
    free_query(query_block);
  }
}


my_bool Query_cache::register_all_tables(Query_cache_block *block,
					 TABLE_LIST *tables_used,
					 TABLE_COUNTER_TYPE tables)
{
  TABLE_COUNTER_TYPE n;
  DBUG_PRINT("qcache", ("register tables block 0x%lx, n %d, header %x",
		      (ulong) block, (int) tables,
		      (int) ALIGN_SIZE(sizeof(Query_cache_block))));

  Query_cache_block_table *block_table = block->table(0);

  for (n=0; tables_used; tables_used=tables_used->next, n++, block_table++)
  {
    DBUG_PRINT("qcache",
	       ("table %s, db %s, openinfo at 0x%lx, keylen %u, key at 0x%lx",
		tables_used->real_name, tables_used->db,
		(ulong) tables_used->table,
		tables_used->table->key_length,
		(ulong) tables_used->table->table_cache_key));
    block_table->n=n;
    if (!insert_table(tables_used->table->key_length,
		      tables_used->table->table_cache_key, block_table,
		      Query_cache_table::type_convertion(tables_used->table->
							 db_type)))
      break;
    /*
      TODO: (Low priority)
      The following has to be recoded to not test for a specific table
      type but instead call a handler function that does this for us.
      Something like the following:

      tables_used->table->file->register_used_filenames(callback,
							first_argument);
    */
    if (tables_used->table->db_type == DB_TYPE_MRG_MYISAM)
    {
      ha_myisammrg *handler = (ha_myisammrg *) tables_used->table->file;
      MYRG_INFO *file = handler->myrg_info();
      for (MYRG_TABLE *table = file->open_tables;
	   table != file->end_table ;
	   table++)
      {
	char key[MAX_DBKEY_LENGTH];
	uint key_length =filename_2_table_key(key, table->table->filename);
	(++block_table)->n= ++n;
	if (!insert_table(key_length, key, block_table,
			  Query_cache_table::type_convertion(DB_TYPE_MYISAM)))
	  goto err;
      }
    }
  }

err:
  if (tables_used)
  {
    DBUG_PRINT("qcache", ("failed at table %d", (int) n));
    /* Unlink the tables we allocated above */
    for (Query_cache_block_table *tmp = block->table(0) ;
	 tmp != block_table;
	 tmp++)
      unlink_table(tmp);
  }
  return (tables_used == 0);
}

/*
  Insert used tablename in cache
  Returns 0 on error
*/

my_bool
Query_cache::insert_table(uint key_len, char *key,
			  Query_cache_block_table *node,
			  Query_cache_table::query_cache_table_type type)
{
  DBUG_ENTER("Query_cache::insert_table");
  DBUG_PRINT("qcache", ("insert table node 0x%lx, len %d",
		      (ulong)node, key_len));

  Query_cache_block *table_block = ((Query_cache_block *)
				    hash_search(&tables, key, key_len));

  if (table_block == 0)
  {
    DBUG_PRINT("qcache", ("new table block from 0x%lx (%u)",
			(ulong) key, (int) key_len));
    table_block = write_block_data(key_len, (gptr) key,
				   ALIGN_SIZE(sizeof(Query_cache_table)),
				   Query_cache_block::TABLE,
				   1, 1);
    if (table_block == 0)
    {
      DBUG_PRINT("qcache", ("Can't write table name to cache"));
      DBUG_RETURN(0);
    }
    Query_cache_table *header = table_block->table();
    header->type(type);
    double_linked_list_simple_include(table_block,
				      &tables_blocks[type]);
    Query_cache_block_table *list_root = table_block->table(0);
    list_root->n = 0;
    list_root->next = list_root->prev = list_root;
    if (hash_insert(&tables, (const byte *) table_block))
    {
      DBUG_PRINT("qcache", ("Can't insert table to hash"));
      // write_block_data return locked block
      free_memory_block(table_block);
      DBUG_RETURN(0);
    }
    char *db = header->db();
    /*
      TODO: Eliminate strlen() by sending this to the function
      To do this we have to add db_len to the TABLE_LIST and TABLE structures.
    */
    header->table(db + strlen(db) + 1);
  }

  Query_cache_block_table *list_root = table_block->table(0);
  node->next = list_root->next;
  list_root->next = node;
  node->next->prev = node;
  node->prev = list_root;
  node->parent = table_block->table();
  DBUG_RETURN(1);
}


void Query_cache::unlink_table(Query_cache_block_table *node)
{
  node->prev->next = node->next;
  node->next->prev = node->prev;
  Query_cache_block_table *neighbour = node->next;
  if (neighbour->next == neighbour)
  {
    // list is empty (neighbor is root of list)
    Query_cache_block *table_block = neighbour->block();
    double_linked_list_exclude(table_block,
			       &tables_blocks[table_block->table()->type()]);
    hash_delete(&tables,(byte *) table_block);
    free_memory_block(table_block);
  }
}

/*****************************************************************************
  Free memory management
*****************************************************************************/

Query_cache_block *
Query_cache::allocate_block(ulong len, my_bool not_less, ulong min,
			    my_bool under_guard)
{
  DBUG_ENTER("Query_cache::allocate_n_lock_block");
  DBUG_PRINT("qcache", ("len %lu, not less %d, min %lu, uder_guard %d",
		      len, not_less,min,under_guard));

  if (len >= min(query_cache_size, query_cache_limit))
  {
    DBUG_PRINT("qcache", ("Query cache hase only %lu memory and limit %lu",
			query_cache_size, query_cache_limit));
    DBUG_RETURN(0); // in any case we don't have such piece of memory
  }

  if (!under_guard)
    STRUCT_LOCK(&structure_guard_mutex);

  /* Free old queries until we have enough memory to store this block */
  Query_cache_block *block;
  do
  {
    block= get_free_block(len, not_less, min);
  }
  while (block == 0 && !free_old_query());

  if (block != 0)				// If we found a suitable block
  {
    if (block->length > ALIGN_SIZE(len) + min_allocation_unit)
      split_block(block,ALIGN_SIZE(len));
  }

  if (!under_guard)
    STRUCT_UNLOCK(&structure_guard_mutex);
  DBUG_RETURN(block);
}


Query_cache_block *
Query_cache::get_free_block(ulong len, my_bool not_less, ulong min)
{
  Query_cache_block *block = 0, *first = 0;
  DBUG_ENTER("Query_cache::get_free_block");
  DBUG_PRINT("qcache",("length %lu, not_less %d, min %lu", len,
		     (int)not_less, min));

  /* Find block with minimal size > len  */
  uint start = find_bin(len);
  // try matching bin
  if (bins[start].number != 0)
  {
    Query_cache_block *list = bins[start].free_blocks;
    first = list;
    while (first->next != list && first->length < len)
      first=first->next;
    if (first->length >= len)
      block=first;
  }
  if (block == 0 && start > 0)
  {
    DBUG_PRINT("qcache",("Try bins with bigger block size"));
    // Try more big bins
    int i = start - 1;
    while (i > 0 && bins[i].number == 0)
      i--;
    if (bins[i].number > 0)
      block = bins[i].free_blocks;
  }

  // If no big blocks => try less size (if it is possible)
  if (block == 0 && ! not_less)
  {
    DBUG_PRINT("qcache",("Try to allocate a smaller block"));
    if (first != 0 && first->length > min)
      block = first;
    else
    {
      uint i = start + 1;
      /* bins[mem_bin_num].number contains 1 for easy end test */
      for (i= start+1 ; bins[i].number == 0 ; i++) ;
      if (i < mem_bin_num && bins[i].free_blocks->prev->length >= min)
	block = bins[i].free_blocks->prev;
    }
  }
  if (block != 0)
    exclude_from_free_memory_list(block);

  DBUG_PRINT("qcache",("getting block 0x%lx", (ulong) block));
  DBUG_RETURN(block);
}


void Query_cache::free_memory_block(Query_cache_block *block)
{
  DBUG_ENTER("Query_cache::free_n_unlock_memory_block");
  block->used=0;
  DBUG_PRINT("qcache",("first_block 0x%lx, block 0x%lx, pnext 0x%lx pprev 0x%lx",
		     (ulong) first_block, (ulong) block,block->pnext,
		     (ulong) block->pprev));

  if (block->pnext != first_block && block->pnext->is_free())
    block = join_free_blocks(block, block->pnext);
  if (block != first_block && block->pprev->is_free())
    block = join_free_blocks(block->pprev, block->pprev);
  insert_into_free_memory_list(block);
  DBUG_VOID_RETURN;
}


void Query_cache::split_block(Query_cache_block *block,ulong len)
{
  DBUG_ENTER("Query_cache::split_block");
  Query_cache_block *new_block = (Query_cache_block*)(((byte*) block)+len);

  new_block->init(block->length - len);
  block->length=len;
  new_block->pnext = block->pnext;
  block->pnext = new_block;
  new_block->pprev = block;
  new_block->pnext->pprev = new_block;

  insert_into_free_memory_list(new_block);

  DBUG_PRINT("qcache", ("split 0x%lx (%lu) new 0x%lx",
		      (ulong) block, len, (ulong) new_block));
  DBUG_VOID_RETURN;
}


Query_cache_block *
Query_cache::join_free_blocks(Query_cache_block *first_block,
			      Query_cache_block *block_in_list)
{
  Query_cache_block *second_block;
  DBUG_ENTER("Query_cache::join_free_blocks");
  DBUG_PRINT("qcache",
	     ("join first 0x%lx, pnext 0x%lx, in list 0x%lx",
	      (ulong) first_block, (ulong) first_block->pnext,
	      (ulong) block_in_list));

  exclude_from_free_memory_list(block_in_list);
  second_block = first_block->pnext;
  // May be was not free block
  second_block->used=0;
  second_block->destroy();

  first_block->length += second_block->length;
  first_block->pnext = second_block->pnext;
  second_block->pnext->pprev = first_block;

  DBUG_RETURN(first_block);
}


my_bool Query_cache::append_next_free_block(Query_cache_block *block,
					    ulong add_size)
{
  Query_cache_block *next_block = block->pnext;
  DBUG_ENTER("Query_cache::append_next_free_block");
  DBUG_PRINT("enter", ("block 0x%lx, add_size %lu", (ulong) block,
		       add_size));

  if (next_block->is_free())
  {
    ulong old_len = block->length;
    exclude_from_free_memory_list(next_block);
    next_block->destroy();

    block->length += next_block->length;
    block->pnext = next_block->pnext;
    next_block->pnext->pprev = block;

    if (block->length > ALIGN_SIZE(old_len + add_size) + min_allocation_unit)
      split_block(block,ALIGN_SIZE(old_len + add_size));
    DBUG_PRINT("exit", ("block was appended"));
    DBUG_RETURN(1);
  }
  DBUG_RETURN(0);
}


void Query_cache::exclude_from_free_memory_list(Query_cache_block *free_block)
{
  DBUG_ENTER("Query_cache::exclude_from_free_memory_list");
  Query_cache_memory_bin *bin = *((Query_cache_memory_bin **)
				  free_block->data());
  double_linked_list_exclude(free_block, &bin->free_blocks);
  bin->number--;
  free_memory-=free_block->length;
  DBUG_PRINT("qcache",("exclude block 0x%lx, bin 0x%lx", (ulong) free_block,
		     (ulong) bin));
  DBUG_VOID_RETURN;
}

void Query_cache::insert_into_free_memory_list(Query_cache_block *free_block)
{
  DBUG_ENTER("Query_cache::insert_into_free_memory_list");
  uint idx = find_bin(free_block->length);
  insert_into_free_memory_sorted_list(free_block, &bins[idx].free_blocks);
  /*
    We have enough memory in block for storing bin reference due to
    min_allocation_unit choice
  */
  Query_cache_memory_bin **bin_ptr = ((Query_cache_memory_bin**)
				      free_block->data());
  *bin_ptr = bins+idx;
  (*bin_ptr)->number++;
  DBUG_PRINT("qcache",("insert block 0x%lx, bin[%d] 0x%lx",
		     (ulong) free_block, idx, (ulong) *bin_ptr));
  DBUG_VOID_RETURN;
}

uint Query_cache::find_bin(ulong size)
{
  int i;
  DBUG_ENTER("Query_cache::find_bin");
  // Begin small blocks to big (small blocks frequently asked)
  for (i=mem_bin_steps - 1; i > 0 && steps[i-1].size < size; i--) ;
  if (i == 0)
  {
    // first bin not subordinate of common rules
    DBUG_PRINT("qcache", ("first bin (# 0), size %lu",size));
    DBUG_RETURN(0);
  }
  uint bin =  steps[i].idx - (uint)((size - steps[i].size)/steps[i].increment);
  DBUG_PRINT("qcache", ("bin %u step %u, size %lu", bin, i, size));
  DBUG_RETURN(bin);
}


/*****************************************************************************
 Lists management
*****************************************************************************/

void Query_cache::move_to_query_list_end(Query_cache_block *query_block)
{
  DBUG_ENTER("Query_cache::move_to_query_list_end");
  double_linked_list_exclude(query_block, &queries_blocks);
  double_linked_list_simple_include(query_block, &queries_blocks);
  DBUG_VOID_RETURN;
}


void Query_cache::insert_into_free_memory_sorted_list(Query_cache_block *
						      new_block,
						      Query_cache_block **
						      list)
{
  DBUG_ENTER("Query_cache::insert_into_free_memory_sorted_list");
  /*
     list sorted by size in ascendant order, because we need small blocks
     more frequently than bigger ones
  */

  new_block->used = 0;
  new_block->n_tables = 0;
  new_block->type = Query_cache_block::FREE;

  if (*list == 0)
  {
    *list = new_block->next=new_block->prev=new_block;
    DBUG_PRINT("qcache", ("inserted into empty list"));
  }
  else
  {
    Query_cache_block *point = *list;
    if (point->length >= new_block->length)
    {
      point = point->prev;
      *list = new_block;
    }
    else
    {
      /* Find right position in sorted list to put block */
      while (point->next != *list &&
	     point->next->length < new_block->length)
	point=point->next;
    }
    new_block->prev = point;
    new_block->next = point->next;
    new_block->next->prev = new_block;
    point->next = new_block;
  }
  free_memory+=new_block->length;
  DBUG_VOID_RETURN;
}


void
Query_cache::double_linked_list_simple_include(Query_cache_block *point,
						Query_cache_block **
						list_pointer)
{
  DBUG_ENTER("Query_cache::double_linked_list_simple_include");
  DBUG_PRINT("qcache", ("including block 0x%lx", (ulong) point));
  if (*list_pointer == 0)
    *list_pointer=point->next=point->prev=point;
  else
  {
    point->next = (*list_pointer);
    point->prev = (*list_pointer)->prev;
    point->prev->next = point;
    (*list_pointer)->prev = point;
    (*list_pointer) = point;
  }
  DBUG_VOID_RETURN;
}

void
Query_cache::double_linked_list_exclude(Query_cache_block *point,
					Query_cache_block **list_pointer)
{
  DBUG_ENTER("Query_cache::double_linked_list_exclude");
  DBUG_PRINT("qcache", ("excluding block 0x%lx, list 0x%lx",
		      (ulong) point, (ulong) list_pointer));
  if (point->next == point)
    *list_pointer = 0;				// empty list
  else
  {
    point->next->prev = point->prev;
    point->prev->next = point->next;
    if (point == *list_pointer)
      *list_pointer = point->next;
  }
  DBUG_VOID_RETURN;
}


void Query_cache::double_linked_list_join(Query_cache_block *head_tail,
					  Query_cache_block *tail_head)
{
  Query_cache_block *head_head = head_tail->next,
		    *tail_tail	= tail_head->prev;
  head_head->prev = tail_tail;
  head_tail->next = tail_head;
  tail_head->prev = head_tail;
  tail_tail->next = head_head;
}

/*****************************************************************************
 Query
*****************************************************************************/

/*
  if query is cacheable return number tables in query
  (query without tables are not cached)
*/

TABLE_COUNTER_TYPE Query_cache::is_cacheable(THD *thd, uint32 query_len,
					     char *query,
					     LEX *lex, TABLE_LIST *tables_used)
{
  TABLE_COUNTER_TYPE tables = 0;
  DBUG_ENTER("Query_cache::is_cacheable");

  if (lex->sql_command == SQLCOM_SELECT &&
      thd->temporary_tables == 0 &&
      (thd->query_cache_type == 1 ||
       (thd->query_cache_type == 2 && (lex->select->options &
				       OPTION_TO_QUERY_CACHE))) &&
      thd->safe_to_cache_query)
  {
    my_bool has_transactions = 0;
    DBUG_PRINT("qcache", ("options %lx %lx, type %u",
			OPTION_TO_QUERY_CACHE,
			lex->select->options,
			(int) thd->query_cache_type));

    for (; tables_used; tables_used=tables_used->next)
    {
      tables++;
      DBUG_PRINT("qcache", ("table %s, db %s, type %u",
			  tables_used->real_name,
			  tables_used->db, tables_used->table->db_type));
      has_transactions = (has_transactions ||
			  tables_used->table->file->has_transactions());

      if (tables_used->table->db_type == DB_TYPE_MRG_ISAM)
      {
	DBUG_PRINT("qcache", ("select not cacheable: used MRG_ISAM table(s)"));
	DBUG_RETURN(0);
      }
      if (tables_used->table->db_type == DB_TYPE_MRG_MYISAM)
      {
	ha_myisammrg *handler = (ha_myisammrg *)tables_used->table->file;
	MYRG_INFO *file = handler->myrg_info();
	tables+= (file->end_table - file->open_tables);
      }
    }

    if ((thd->options & (OPTION_NOT_AUTO_COMMIT | OPTION_BEGIN)) &&
	has_transactions)
    {
      DBUG_PRINT("qcache", ("not in autocommin mode"));
      DBUG_RETURN(0);
    }
    DBUG_PRINT("qcache", ("select is using %d tables", tables));
    DBUG_RETURN(tables);
  }

  DBUG_PRINT("qcache",
	     ("not interesting query: %d or not cacheable, options %lx %lx, type %u",
	      (int) lex->sql_command,
	      OPTION_TO_QUERY_CACHE,
	      lex->select->options,
	      (int) thd->query_cache_type));
  DBUG_RETURN(0);
}


/*****************************************************************************
  Packing
*****************************************************************************/

void Query_cache::pack_cache()
{
  STRUCT_LOCK(&structure_guard_mutex);
  byte *border = 0;
  Query_cache_block *before = 0;
  ulong gap = 0;
  my_bool ok = 1;
  Query_cache_block *block = first_block;
  DBUG_ENTER("Query_cache::pack_cache");
  DUMP(this);

  if (first_block)
  {
    do
    {
      ok = move_by_type(&border, &before, &gap, block);
      block = block->pnext;
    } while (ok && block != first_block);

    if (border != 0)
    {
      Query_cache_block *new_block = (Query_cache_block *) border;
      new_block->init(gap);
      new_block->pnext = before->pnext;
      before->pnext = new_block;
      new_block->pprev = before;
      new_block->pnext->pprev = new_block;
      insert_into_free_memory_list(new_block);
    }
    DUMP(this);
  }
  STRUCT_UNLOCK(&structure_guard_mutex);
  DBUG_VOID_RETURN;
}


my_bool Query_cache::move_by_type(byte **border,
				  Query_cache_block **before, ulong *gap,
				  Query_cache_block *block)
{
  DBUG_ENTER("Query_cache::move_by_type");

  my_bool ok = 1;
  switch (block->type) {
  case Query_cache_block::FREE:
  {
    DBUG_PRINT("qcache", ("block 0x%lx FREE", (ulong) block));
    if (*border == 0)
    {
      *border = (byte *) block;
      *before = block->pprev;
      DBUG_PRINT("qcache", ("gap beginning here"));
    }
    exclude_from_free_memory_list(block);
    *gap +=block->length;
    block->pprev->pnext=block->pnext;
    block->pnext->pprev=block->pprev;
    block->destroy();
    DBUG_PRINT("qcache", ("added to gap (%lu)", *gap));
    break;
  }
  case Query_cache_block::TABLE:
  {
    DBUG_PRINT("qcache", ("block 0x%lx TABLE", (ulong) block));
    if (*border == 0)
      break;
    ulong len = block->length, used = block->used;
    Query_cache_block_table *list_root = block->table(0);
    Query_cache_block_table *tprev = list_root->prev,
			    *tnext = list_root->next;
    Query_cache_block *prev = block->prev,
		      *next = block->next,
		      *pprev = block->pprev,
		      *pnext = block->pnext,
		      *new_block =(Query_cache_block *) *border;
    char *data = (char*) block->data();
    byte *key;
    uint key_length;
    key=query_cache_table_get_key((byte*) block, &key_length,0);
    hash_search(&tables, key, key_length);

    block->destroy();
    new_block->init(len);
    new_block->type=Query_cache_block::TABLE;
    new_block->used=used;
    new_block->n_tables=1;
    memcpy((char*) new_block->data(), data, len-new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    if (tables_blocks[new_block->table()->type()] == block)
      tables_blocks[new_block->table()->type()] = new_block;

    Query_cache_block_table *nlist_root = new_block->table(0);
    nlist_root->n = 0;
    nlist_root->next = (tnext == list_root ? nlist_root : tnext);
    nlist_root->prev = (tprev == list_root ? nlist_root: tnext);
    tnext->prev = list_root;
    tprev->next = list_root;
    *border += len;
    *before = new_block;
    /* Fix hash to point at moved block */
    hash_replace(&tables, tables.current_record, (byte*) new_block);

    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  case Query_cache_block::QUERY:
  {
    DBUG_PRINT("qcache", ("block 0x%lx QUERY", (ulong) block));
    if (*border == 0)
      break;
    BLOCK_LOCK_WR(block);
    ulong len = block->length, used = block->used;
    TABLE_COUNTER_TYPE n_tables = block->n_tables;
    Query_cache_block	*prev = block->prev,
			*next = block->next,
			*pprev = block->pprev,
			*pnext = block->pnext,
			*new_block =(Query_cache_block*) *border;
    char *data = (char*) block->data();
    Query_cache_block *first_result_block = ((Query_cache_query *)
					     block->data())->result();
    byte *key;
    uint key_length;
    key=query_cache_query_get_key((byte*) block, &key_length,0);
    hash_search(&queries, key, key_length);

    memcpy((char*) new_block->table(0), (char*) block->table(0),
	   ALIGN_SIZE(n_tables*sizeof(Query_cache_block_table)));
    block->query()->unlock_n_destroy();
    block->destroy();
    new_block->init(len);
    new_block->type=Query_cache_block::QUERY;
    new_block->used=used;
    new_block->n_tables=n_tables;
    memcpy((char*) new_block->data(), data, len - new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    if (queries_blocks == block)
      queries_blocks = new_block;
    for (TABLE_COUNTER_TYPE j=0; j < n_tables; j++)
    {
      Query_cache_block_table *block_table = new_block->table(j);
      block_table->next->prev = block_table;
      block_table->prev->next = block_table;
    }
    DBUG_PRINT("qcache", ("after circle tt"));
    *border += len;
    *before = new_block;
    new_block->query()->result(first_result_block);
    if (first_result_block != 0)
    {
      Query_cache_block *result_block = first_result_block;
      do
      {
	result_block->result()->parent(new_block);
	result_block = result_block->next;
      } while ( result_block != first_result_block );
    }
    NET *net = new_block->query()->writer();
    if (net != 0)
    {
      net->query_cache_query = (gptr) new_block;
    }
    /* Fix hash to point at moved block */
    hash_replace(&queries, queries.current_record, (byte*) new_block);
    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  case Query_cache_block::RES_INCOMPLETE:
  case Query_cache_block::RES_BEG:
  case Query_cache_block::RES_CONT:
  case Query_cache_block::RESULT:
  {
    DBUG_PRINT("qcache", ("block 0x%lx RES* (%d)", (ulong) block,
			(int) block->type));
    if (*border == 0)
      break;
    Query_cache_block *query_block = block->result()->parent(),
		      *next = block->next,
		      *prev = block->prev;
    Query_cache_block::block_type type = block->type;
    BLOCK_LOCK_WR(query_block);
    ulong len = block->length, used = block->used;
    Query_cache_block *pprev = block->pprev,
		      *pnext = block->pnext,
		      *new_block =(Query_cache_block*) *border;
    char *data = (char*) block->data();
    block->destroy();
    new_block->init(len);
    new_block->type=type;
    new_block->used=used;
    memcpy((char*) new_block->data(), data, len - new_block->headers_len());
    relink(block, new_block, next, prev, pnext, pprev);
    new_block->result()->parent(query_block);
    Query_cache_query *query = query_block->query();
    if (query->result() == block)
      query->result(new_block);
    *border += len;
    *before = new_block;
    /* If result writing complete && we have free space in block */
    ulong free_space = new_block->length - new_block->used;
    if (query->result()->type == Query_cache_block::RESULT &&
	new_block->length > new_block->used &&
	*gap + free_space > min_allocation_unit &&
	new_block->length - free_space > min_allocation_unit)
    {
      *border -= free_space;
      *gap += free_space;
      new_block->length -= free_space;
    }
    BLOCK_UNLOCK_WR(query_block);
    DBUG_PRINT("qcache", ("moved %lu bytes to 0x%lx, new gap at 0x%lx",
			len, (ulong) new_block, (ulong) *border));
    break;
  }
  default:
    DBUG_PRINT("error", ("unexpected block type %d, block 0x%lx",
			 (int)block->type, (ulong) block));
    ok = 0;
  }
  DBUG_RETURN(ok);
}


void Query_cache::relink(Query_cache_block *oblock,
			 Query_cache_block *nblock,
			 Query_cache_block *next, Query_cache_block *prev,
			 Query_cache_block *pnext, Query_cache_block *pprev)
{
  nblock->prev = (prev == oblock ? nblock : prev); //check pointer to himself
  nblock->next = (next == oblock ? nblock : next);
  prev->next=nblock;
  next->prev=nblock;
  nblock->pprev = pprev; // Physical pointer to himself have only 1 free block
  nblock->pnext = pnext;
  pprev->pnext=nblock;
  pnext->pprev=nblock;
}


my_bool Query_cache::join_results(ulong join_limit)
{
  my_bool has_moving = 0;
  DBUG_ENTER("Query_cache::join_results");

  STRUCT_LOCK(&structure_guard_mutex);
  if (queries_blocks != 0)
  {
    Query_cache_block *block = queries_blocks;
    do
    {
      Query_cache_query *header = block->query();
      if (header->result() != 0 &&
	  header->result()->type == Query_cache_block::RESULT &&
	  header->length() > join_limit)
      {
	Query_cache_block *new_result_block =
	  get_free_block(header->length() +
			 ALIGN_SIZE(sizeof(Query_cache_block)) +
			 ALIGN_SIZE(sizeof(Query_cache_result)), 1, 0);
	if (new_result_block != 0)
	{
	  has_moving = 1;
	  Query_cache_block *first_result = header->result();
	  ulong new_len = (header->length() +
			   ALIGN_SIZE(sizeof(Query_cache_block)) +
			   ALIGN_SIZE(sizeof(Query_cache_result)));
	  if (new_result_block->length >
	      ALIGN_SIZE(new_len) + min_allocation_unit)
	    split_block(new_result_block, ALIGN_SIZE(new_len));
	  BLOCK_LOCK_WR(block);
	  header->result(new_result_block);
	  new_result_block->type = Query_cache_block::RESULT;
	  new_result_block->n_tables = 0;
	  new_result_block->used = new_len;

	  new_result_block->next = new_result_block->prev = new_result_block;
	  DBUG_PRINT("qcache", ("new block %lu/%lu (%lu)",
			      new_result_block->length,
			      new_result_block->used,
			      header->length()));

	  Query_cache_result *new_result = new_result_block->result();
	  new_result->parent(block);
	  byte *write_to = (byte*) new_result->data();
	  Query_cache_block *result_block = first_result;
	  do
	  {
	    ulong len = (result_block->used - result_block->headers_len() -
			 ALIGN_SIZE(sizeof(Query_cache_result)));
	    DBUG_PRINT("loop", ("add block %lu/%lu (%lu)",
				result_block->length,
				result_block->used,
				len));
	    memcpy((char *) write_to,
		   (char*) result_block->result()->data(),
		   len);
	    write_to += len;
	    Query_cache_block *old_result_block = result_block;
	    result_block = result_block->next;
	    free_memory_block(old_result_block);
	  } while (result_block != first_result);
	  BLOCK_UNLOCK_WR(block);
	}
      }
      block = block->next;
    } while ( block != queries_blocks );
  }
  STRUCT_UNLOCK(&structure_guard_mutex);
  DBUG_RETURN(has_moving);
}


uint Query_cache::filename_2_table_key (char *key, const char *path)
{
  char tablename[FN_REFLEN+2], *filename, *dbname;
  Query_cache_block *table_block;
  uint db_length;
  DBUG_ENTER("Query_cache::filename_2_table_key");

  /* Safety if filename didn't have a directory name */
  tablename[0]= FN_LIBCHAR;
  tablename[1]= FN_LIBCHAR;
  /* Convert filename to this OS's format in tablename */
  fn_format(tablename + 2, path, "", "", MY_REPLACE_EXT);
  filename=  tablename + dirname_length(tablename + 2) + 2;
  /* Find start of databasename */
  for (dbname= filename - 2 ; dbname[-1] != FN_LIBCHAR ; dbname--) ;
  db_length= (filename - dbname) - 1; 
  DBUG_PRINT("qcache", ("table '%-.*s.%s'", db_length, dbname, filename));

  DBUG_RETURN((uint) (strmov(strmake(key, dbname, db_length) + 1,
			     filename) -key) + 1);
}


/****************************************************************************
  Functions to be used when debugging
****************************************************************************/

#ifndef DBUG_OFF

void Query_cache::wreck(uint line, const char *message)
{
  DBUG_ENTER("Query_cache::wreck");
  query_cache_size = 0;
  if (*message)
    DBUG_PRINT("error", (" %s", message));
  DBUG_PRINT("warning", ("=================================="));
  DBUG_PRINT("warning", ("%5d QUERY CACHE WRECK => DISABLED",line));
  DBUG_PRINT("warning", ("=================================="));
  current_thd->killed = 1;
  bins_dump();
  cache_dump();
  DBUG_VOID_RETURN;
}


void Query_cache::bins_dump()
{
  uint i;
  DBUG_PRINT("qcache", ("mem_bin_num=%u, mem_bin_steps=%u",
		      mem_bin_num, mem_bin_steps));
  DBUG_PRINT("qcache", ("-------------------------"));
  DBUG_PRINT("qcache", ("      size idx       step"));
  DBUG_PRINT("qcache", ("-------------------------"));
  for (i=0; i < mem_bin_steps; i++)
  {
    DBUG_PRINT("qcache", ("%10lu %3d %10lu", steps[i].size, steps[i].idx,
			steps[i].increment));
  }
  DBUG_PRINT("qcache", ("-------------------------"));
  DBUG_PRINT("qcache", ("      size num"));
  DBUG_PRINT("qcache", ("-------------------------"));
  for (i=0; i < mem_bin_num; i++)
  {
    DBUG_PRINT("qcache", ("%10lu %3d 0x%lx", bins[i].size, bins[i].number,
			(ulong)&(bins[i])));
    if (bins[i].free_blocks)
    {
      Query_cache_block *block = bins[i].free_blocks;
      do{
	DBUG_PRINT("qcache", ("\\-- %lu 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
			    block->length, (ulong)block,
			    (ulong)block->next, (ulong)block->prev,
			    (ulong)block->pnext, (ulong)block->pprev));
	block = block->next;
      } while ( block != bins[i].free_blocks );
    }
  }
  DBUG_PRINT("qcache", ("-------------------------"));
}


void Query_cache::cache_dump()
{
  DBUG_PRINT("qcache", ("-------------------------------------"));
  DBUG_PRINT("qcache", ("    length       used t nt"));
  DBUG_PRINT("qcache", ("-------------------------------------"));
  Query_cache_block *i = first_block;
  do
  {
    DBUG_PRINT("qcache",
	       ("%10lu %10lu %1d %2d 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
		i->length, i->used, (int)i->type,
		i->n_tables, (ulong)i,
		(ulong)i->next, (ulong)i->prev, (ulong)i->pnext,
		(ulong)i->pprev));
    i = i->pnext;
  } while ( i != first_block );
  DBUG_PRINT("qcache", ("-------------------------------------"));
}


void Query_cache::queries_dump()
{
  DBUG_PRINT("qcache", ("------------------"));
  DBUG_PRINT("qcache", (" QUERIES"));
  DBUG_PRINT("qcache", ("------------------"));
  if (queries_blocks != 0)
  {
    Query_cache_block *block = queries_blocks;
    do
    {
      uint len;
      char *str = (char*) query_cache_query_get_key((byte*) block, &len, 0);
      byte flags = (byte) str[len-1];
      DBUG_PRINT("qcache", ("%u (%u,%u) %.*s",len,
			  ((flags & QUERY_CACHE_CLIENT_LONG_FLAG_MASK)? 1:0),
			  (flags & QUERY_CACHE_CHARSET_CONVERT_MASK), len,
			    str));
      DBUG_PRINT("qcache", ("-b- 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx", (ulong) block,
			    (ulong) block->next, (ulong) block->prev,
			    (ulong)block->pnext, (ulong)block->pprev));

      for (TABLE_COUNTER_TYPE t = 0; t < block->n_tables; t++)
      {
	Query_cache_table *table = block->table(t)->parent;
	DBUG_PRINT("qcache", ("-t- '%s' '%s'", table->db(), table->table()));
      }
      Query_cache_query *header = block->query();
      if (header->result())
      {
	Query_cache_block *result_block = header->result();
	Query_cache_block *result_beg = result_block;
	do
	{
	  DBUG_PRINT("qcache", ("-r- %u %lu/%lu 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx",
			      (uint) result_block->type,
			      result_block->length, result_block->used,
			      (ulong) result_block,
			      (ulong) result_block->next,
			      (ulong) result_block->prev,
			      (ulong) result_block->pnext,
			      (ulong) result_block->pprev));
	  result_block = result_block->next;
	} while ( result_block != result_beg );
      }
    } while ((block=block->next) != queries_blocks);
  }
  else
  {
    DBUG_PRINT("qcache", ("no queries in list"));
  }
  DBUG_PRINT("qcache", ("------------------"));
}


void Query_cache::tables_dump()
{
  DBUG_PRINT("qcache", ("--------------------"));
  DBUG_PRINT("qcache", ("TABLES"));
  DBUG_PRINT("qcache", ("--------------------"));
  for (int i=0; i < (int) Query_cache_table::TYPES_NUMBER; i++)
  {
    DBUG_PRINT("qcache", ("--- type %u", i));
    if (tables_blocks[i] != 0)
    {
      Query_cache_block *table_block = tables_blocks[i];
      do
      {
	Query_cache_table *table = table_block->table();
	DBUG_PRINT("qcache", ("'%s' '%s'", table->db(), table->table()));
	table_block = table_block->next;
      } while ( table_block != tables_blocks[i]);
    }
    else
      DBUG_PRINT("qcache", ("no tables in list"));
  }
  DBUG_PRINT("qcache", ("--------------------"));
}
#endif /* DBUG_OFF */