mariadb/sql/examples/ha_archive.cc

/* Copyright (C) 2003 MySQL 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 */

#ifdef __GNUC__
#pragma implementation        // gcc: Class implementation
#endif

#include <mysql_priv.h>

#ifdef HAVE_ARCHIVE_DB
#include "ha_archive.h"

/*
  First, if you want to understand storage engines you should look at 
  ha_example.cc and ha_example.h. 
  This example was written as a test case for a customer who needed
  a storage engine without indexes that could compress data very well.
  So, welcome to a completely compressed storage engine. This storage
  engine only does inserts. No replace, deletes, or updates. All reads are 
  complete table scans. Compression is done through gzip (bzip compresses
  better, but only marginally, if someone asks I could add support for
  it too, but beaware that it costs a lot more in CPU time then gzip).
  
  We keep a file pointer open for each instance of ha_archive for each read
  but for writes we keep one open file handle just for that. We flush it
  only if we have a read occur. gzip handles compressing lots of records
  at once much better then doing lots of little records between writes.
  It is possible to not lock on writes but this would then mean we couldn't
  handle bulk inserts as well (that is if someone was trying to read at
  the same time since we would want to flush).

  No attempts at durability are made. You can corrupt your data.

  For performance as far as table scans go it is quite fast. I don't have
  good numbers but locally it has out performed both Innodb and MyISAM. For
  Innodb the question will be if the table can be fit into the buffer
  pool. For MyISAM its a question of how much the file system caches the
  MyISAM file. With enough free memory MyISAM is faster. Its only when the OS
  doesn't have enough memory to cache entire table that archive turns out 
  to be any faster. For writes it is always a bit slower then MyISAM. It has no
  internal limits though for row length.

  Examples between MyISAM (packed) and Archive.

  Table with 76695844 identical rows:
  29680807 a_archive.ARZ
  920350317 a.MYD


  Table with 8991478 rows (all of Slashdot's comments):
  1922964506 comment_archive.ARZ
  2944970297 comment_text.MYD


  TODO:
   Add bzip optional support.
   Allow users to set compression level.
   Add truncate table command.
   Implement versioning, should be easy.
   Implement optimize so we can fix broken tables.
   Allow for errors, find a way to mark bad rows.
   See if during an optimize you can make the table smaller.
   Talk to the gzip guys, come up with a writable format so that updates are doable
     without switching to a block method.
   Add optional feature so that rows can be flushed at interval (which will cause less
   compression but may speed up ordered searches).

    -Brian
*/

/* Variables for archive share methods */
pthread_mutex_t archive_mutex;
static HASH archive_open_tables;
static int archive_init= 0;

/* The file extension */
#define ARZ ".ARZ"

/*
  Used for hash table that tracks open tables.
*/
static byte* archive_get_key(ARCHIVE_SHARE *share,uint *length,
                             my_bool not_used __attribute__((unused)))
{
  *length=share->table_name_length;
  return (byte*) share->table_name;
}


/*
  Example of simple lock controls.
  See ha_example.cc for a description.
*/
static ARCHIVE_SHARE *get_share(const char *table_name, TABLE *table)
{
  ARCHIVE_SHARE *share;
  uint length;
  char *tmp_name;

  if (!archive_init)
  {
    /* Hijack a mutex for init'ing the storage engine */
    pthread_mutex_lock(&LOCK_mysql_create_db);
    if (!archive_init)
    {
      archive_init++;
      VOID(pthread_mutex_init(&archive_mutex,MY_MUTEX_INIT_FAST));
      (void) hash_init(&archive_open_tables,system_charset_info,32,0,0,
                       (hash_get_key) archive_get_key,0,0);
    }
    pthread_mutex_unlock(&LOCK_mysql_create_db);
  }
  pthread_mutex_lock(&archive_mutex);
  length=(uint) strlen(table_name);

  if (!(share=(ARCHIVE_SHARE*) hash_search(&archive_open_tables,
                                           (byte*) table_name,
                                           length)))
  {
    if (!(share=(ARCHIVE_SHARE *)
          my_multi_malloc(MYF(MY_WME | MY_ZEROFILL),
                          &share, sizeof(*share),
                          &tmp_name, length+1,
                          NullS))) 
    {
      pthread_mutex_unlock(&archive_mutex);
      return NULL;
    }

    share->use_count=0;
    share->table_name_length=length;
    share->table_name=tmp_name;
    fn_format(share->data_file_name,table_name,"",ARZ,MY_REPLACE_EXT|MY_UNPACK_FILENAME);
    strmov(share->table_name,table_name);
    /* 
      It is expensive to open and close the data files and since you can't have
      a gzip file that can be both read and written we keep a writer open
      that is shared amoung all open tables.
    */
    if ((share->archive_write= gzopen(share->data_file_name, "ab")) == NULL)
      goto error;
    if (my_hash_insert(&archive_open_tables, (byte*) share))
      goto error;
    thr_lock_init(&share->lock);
    if (pthread_mutex_init(&share->mutex,MY_MUTEX_INIT_FAST))
      goto error2;
  }
  share->use_count++;
  pthread_mutex_unlock(&archive_mutex);

  return share;

error2:
  thr_lock_delete(&share->lock);
  /* We close, but ignore errors since we already have errors */
  (void)gzclose(share->archive_write);
error:
  pthread_mutex_unlock(&archive_mutex);
  my_free((gptr) share, MYF(0));

  return NULL;
}


/* 
  Free lock controls.
  See ha_example.cc for a description.
*/
static int free_share(ARCHIVE_SHARE *share)
{
  int rc= 0;
  pthread_mutex_lock(&archive_mutex);
  if (!--share->use_count)
  {
    hash_delete(&archive_open_tables, (byte*) share);
    thr_lock_delete(&share->lock);
    pthread_mutex_destroy(&share->mutex);
    my_free((gptr) share, MYF(0));
    if (gzclose(share->archive_write) == Z_ERRNO)
      rc= -1;
  }
  pthread_mutex_unlock(&archive_mutex);

  return rc;
}


/* 
  We just implement one additional file extension.
*/
const char **ha_archive::bas_ext() const
{ static const char *ext[]= { ARZ, NullS }; return ext; }


/* 
  When opening a file we:
  Create/get our shared structure.
  Init out lock.
  We open the file we will read from.
  Set the size of ref_length.
*/
int ha_archive::open(const char *name, int mode, uint test_if_locked)
{
  DBUG_ENTER("ha_archive::open");

  if (!(share= get_share(name, table)))
    DBUG_RETURN(1);
  thr_lock_data_init(&share->lock,&lock,NULL);

  if ((archive= gzopen(share->data_file_name, "rb")) == NULL)
  {
    (void)free_share(share); //We void since we already have an error
    DBUG_RETURN(-1);
  }

  DBUG_RETURN(0);
}


/*
  Closes the file. We first close this storage engines file handle to the
  archive and then remove our reference count to the table (and possibly
  free it as well).
  */
int ha_archive::close(void)
{
  DBUG_ENTER("ha_archive::close");
  int rc= 0;
  if (gzclose(archive) == Z_ERRNO)
    rc =-1;
  rc |= free_share(share);
  DBUG_RETURN(rc);
}


/*
  We create our data file here. The format is pretty simple. The first bytes in
  any file are the version number. Currently we do nothing with this, but in
  the future this gives us the ability to figure out version if we change the
  format at all. After the version we starting writing our rows. Unlike other
  storage engines we do not "pack" our data. Since we are about to do a general
  compression, packing would just be a waste of CPU time. If the table has blobs
  they are written after the row in the order of creation. 
  So to read a row we:
    Read the version
    Read the record and copy it into buf
    Loop through any blobs and read them
  */
int ha_archive::create(const char *name, TABLE *table_arg, HA_CREATE_INFO *create_info)
{
  File create_file;
  char name_buff[FN_REFLEN];
  size_t written;
  DBUG_ENTER("ha_archive::create");

  if ((create_file= my_create(fn_format(name_buff,name,"",ARZ,MY_REPLACE_EXT|MY_UNPACK_FILENAME),0,
                               O_RDWR | O_TRUNC,MYF(MY_WME))) < 0)
    DBUG_RETURN(-1);
  if ((archive= gzdopen(create_file, "ab")) == NULL)
  {
    delete_table(name);
    DBUG_RETURN(-1);
  }
  version= ARCHIVE_VERSION;
  written= gzwrite(archive, &version, sizeof(version));
  if (written == 0 || written != sizeof(version))
  {
    delete_table(name);
    DBUG_RETURN(-1);
  }
  if (gzclose(archive))
  {
    delete_table(name);
    DBUG_RETURN(-1);
  }

  DBUG_RETURN(0);
}

/* 
  Look at ha_archive::open() for an explanation of the row format.
  Here we just write out the row.
*/
int ha_archive::write_row(byte * buf)
{
  char *pos;
  z_off_t written;
  DBUG_ENTER("ha_archive::write_row");

  statistic_increment(ha_write_count,&LOCK_status);
  if (table->timestamp_default_now)
    update_timestamp(buf+table->timestamp_default_now-1);
  written= gzwrite(share->archive_write, buf, table->reclength);
  share->dirty= true;
  if (written == 0 || written != table->reclength)
    DBUG_RETURN(-1);

  for (Field_blob **field=table->blob_field ; *field ; field++)
  {
    char *ptr;
    uint32 size= (*field)->get_length();

    (*field)->get_ptr(&ptr);
    written= gzwrite(share->archive_write, ptr, (unsigned)size);
    if (written == 0 || written != size)
      DBUG_RETURN(-1);
  }

  DBUG_RETURN(0);
}


/*
  All calls that need to scan the table start with this method. If we are told
  that it is a table scan we rewind the file to the beginning, otherwise
  we assume the position will be set.
*/
int ha_archive::rnd_init(bool scan)
{
  DBUG_ENTER("ha_archive::rnd_init");
  int read; // gzread() returns int, and we use this to check the header

  /* We rewind the file so that we can read from the beginning if scan */
  if(scan)
  {
    records= 0;
    if (gzrewind(archive))
      DBUG_RETURN(HA_ERR_CRASHED_ON_USAGE);
  }

  /* 
    If dirty, we lock, and then reset/flush the data.
    I found that just calling gzflush() doesn't always work.
  */
  if (share->dirty == true)
  {
    pthread_mutex_lock(&share->mutex);
    if (share->dirty == true)
    {
/* I was having problems with OSX, but it worked for 10.3 so I am wrapping this with and ifdef */
#ifdef BROKEN_GZFLUSH
      gzclose(share->archive_write);
      if ((share->archive_write= gzopen(share->data_file_name, "ab")) == NULL)
      {
        pthread_mutex_unlock(&share->mutex);
        DBUG_RETURN(-1);
      }
#else
      gzflush(share->archive_write, Z_SYNC_FLUSH);
#endif
      share->dirty= false;
    }
    pthread_mutex_unlock(&share->mutex);
  }
  
  /* 
    At the moment we just check the size of version to make sure the header is 
    intact.
  */
  if (scan)
  {
    read= gzread(archive, &version, sizeof(version));
    if (read == 0 || read != sizeof(version))
      DBUG_RETURN(-1);
  }

  DBUG_RETURN(0);
}


/*
  This is the method that is used to read a row. It assumes that the row is 
  positioned where you want it.
*/
int ha_archive::get_row(byte *buf)
{
  int read; // Bytes read, gzread() returns int
  char *last;
  size_t total_blob_length= 0;
  DBUG_ENTER("ha_archive::get_row");

  read= gzread(archive, buf, table->reclength);

  /* If we read nothing we are at the end of the file */
  if (read == 0)
    DBUG_RETURN(HA_ERR_END_OF_FILE);

  /* If the record is the wrong size, the file is probably damaged */
  if (read != table->reclength)
    DBUG_RETURN(HA_ERR_CRASHED_ON_USAGE);

  /* Calculate blob length, we use this for our buffer */
  for (Field_blob **field=table->blob_field; *field ; field++)
    total_blob_length += (*field)->get_length();

  /* Adjust our row buffer if we need be */
  buffer.alloc(total_blob_length);
  last= (char *)buffer.ptr();

  /* Loop through our blobs and read them */
  for (Field_blob **field=table->blob_field; *field ; field++)
  {
    size_t size= (*field)->get_length();
    read= gzread(archive, last, size);
    if (read == 0 || read != size)
      DBUG_RETURN(HA_ERR_CRASHED_ON_USAGE);
    (*field)->set_ptr(size, last);
    last += size;
  }
  DBUG_RETURN(0);
}

/* 
  Called during ORDER BY. Its position is either from being called sequentially
  or by having had ha_archive::rnd_pos() called before it is called.
*/
int ha_archive::rnd_next(byte *buf)
{
  DBUG_ENTER("ha_archive::rnd_next");
  int rc;

  statistic_increment(ha_read_rnd_next_count,&LOCK_status);
  current_position= gztell(archive);
  rc= get_row(buf);
  if (!(HA_ERR_END_OF_FILE == rc))
    records++;

  DBUG_RETURN(rc);
}


/* 
  Thanks to the table flag HA_REC_NOT_IN_SEQ this will be called after
  each call to ha_archive::rnd_next() if an ordering of the rows is
  needed.
*/
void ha_archive::position(const byte *record)
{
  DBUG_ENTER("ha_archive::position");
  ha_store_ptr(ref, ref_length, current_position);
  DBUG_VOID_RETURN;
}


/*
  This is called after a table scan for each row if the results of the scan need
  to be ordered. It will take *pos and use it to move the cursor in the file so
  that the next row that is called is the correctly ordered row.
*/
int ha_archive::rnd_pos(byte * buf, byte *pos)
{
  DBUG_ENTER("ha_archive::rnd_pos");
  statistic_increment(ha_read_rnd_count,&LOCK_status);
  current_position= ha_get_ptr(pos, ref_length);
  z_off_t seek= gzseek(archive, current_position, SEEK_SET);

  DBUG_RETURN(get_row(buf));
}

/******************************************************************************

  Everything below here is default, please look at ha_example.cc for 
  descriptions.

 ******************************************************************************/

int ha_archive::update_row(const byte * old_data, byte * new_data)
{

  DBUG_ENTER("ha_archive::update_row");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::delete_row(const byte * buf)
{
  DBUG_ENTER("ha_archive::delete_row");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::index_read(byte * buf, const byte * key,
                           uint key_len __attribute__((unused)),
                           enum ha_rkey_function find_flag
                           __attribute__((unused)))
{
  DBUG_ENTER("ha_archive::index_read");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::index_read_idx(byte * buf, uint index, const byte * key,
                               uint key_len __attribute__((unused)),
                               enum ha_rkey_function find_flag
                               __attribute__((unused)))
{
  DBUG_ENTER("ha_archive::index_read_idx");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}


int ha_archive::index_next(byte * buf)
{
  DBUG_ENTER("ha_archive::index_next");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::index_prev(byte * buf)
{
  DBUG_ENTER("ha_archive::index_prev");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::index_first(byte * buf)
{
  DBUG_ENTER("ha_archive::index_first");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}

int ha_archive::index_last(byte * buf)
{
  DBUG_ENTER("ha_archive::index_last");
  DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}


void ha_archive::info(uint flag)
{
  DBUG_ENTER("ha_archive::info");

  /* This is a lie, but you don't want the optimizer to see zero or 1 */
  if (records < 2) 
    records= 2;

  DBUG_VOID_RETURN;
}

int ha_archive::extra(enum ha_extra_function operation)
{
  DBUG_ENTER("ha_archive::extra");
  DBUG_RETURN(0);
}

int ha_archive::reset(void)
{
  DBUG_ENTER("ha_archive::reset");
  DBUG_RETURN(0);
}


int ha_archive::external_lock(THD *thd, int lock_type)
{
  DBUG_ENTER("ha_archive::external_lock");
  DBUG_RETURN(0);
}

THR_LOCK_DATA **ha_archive::store_lock(THD *thd,
                                       THR_LOCK_DATA **to,
                                       enum thr_lock_type lock_type)
{
  if (lock_type != TL_IGNORE && lock.type == TL_UNLOCK)
    lock.type=lock_type;
  *to++= &lock;
  return to;
}

ha_rows ha_archive::records_in_range(int inx,
                                     const byte *start_key,uint start_key_len,
                                     enum ha_rkey_function start_search_flag,
                                     const byte *end_key,uint end_key_len,
                                     enum ha_rkey_function end_search_flag)
{
  DBUG_ENTER("ha_archive::records_in_range ");
  DBUG_RETURN(records); // HA_ERR_WRONG_COMMAND 
}
#endif /* HAVE_ARCHIVE_DB */