mariadb/sql/uniques.cc

/* Copyright (C) 2001 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 */

/*
  Function to handle quick removal of duplicates
  This code is used when doing multi-table deletes to find the rows in
  reference tables that needs to be deleted.

  The basic idea is as follows:

  Store first all strings in a binary tree, ignoring duplicates.
  When the tree uses more memory than 'max_heap_table_size',
  write the tree (in sorted order) out to disk and start with a new tree.
  When all data has been generated, merge the trees (removing any found
  duplicates).

  The unique entries will be returned in sort order, to ensure that we do the
  deletes in disk order.
*/

#include "mysql_priv.h"
#include "sql_sort.h"


int unique_write_to_file(gptr key, element_count count, Unique *unique)
{
  /*
    Use unique->size (size of element stored in the tree) and not 
    unique->tree.size_of_element. The latter is different from unique->size 
    when tree implementation chooses to store pointer to key in TREE_ELEMENT
    (instead of storing the element itself there)
  */
  return my_b_write(&unique->file, (byte*) key,
		    unique->size) ? 1 : 0;
}

int unique_write_to_ptrs(gptr key, element_count count, Unique *unique)
{
  memcpy(unique->record_pointers, key, unique->size);
  unique->record_pointers+=unique->size;
  return 0;
}

Unique::Unique(qsort_cmp2 comp_func, void * comp_func_fixed_arg,
	       uint size_arg, ulong max_in_memory_size_arg)
  :max_in_memory_size(max_in_memory_size_arg), size(size_arg), elements(0)
{
  my_b_clear(&file);
  init_tree(&tree, max_in_memory_size / 16, 0, size, comp_func, 0, NULL,
	    comp_func_fixed_arg);
  /* If the following fail's the next add will also fail */
  my_init_dynamic_array(&file_ptrs, sizeof(BUFFPEK), 16, 16);
  /* 
    If you change the following, change it in get_max_elements function, too.
  */
  max_elements= max_in_memory_size / ALIGN_SIZE(sizeof(TREE_ELEMENT)+size);
  open_cached_file(&file, mysql_tmpdir,TEMP_PREFIX, DISK_BUFFER_SIZE,
		   MYF(MY_WME));
}


#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

#ifndef M_E
#define M_E (exp((double)1.0))
#endif

inline double log2_n_fact(double x)
{
  return (2 * (((x)+1)*log(((x)+1)/M_E) + log(2*M_PI*((x)+1))/2 ) / log(2));
}

/*
  Calculate cost of merge_buffers call.

  NOTE
    See comment near Unique::get_use_cost for cost formula derivation.
*/
static double get_merge_buffers_cost(uint* buff_sizes, uint elem_size, 
                                     int last, int f,int t)
{  
  uint sum= 0;
  for (int i=f; i <= t; i++)
    sum+= buff_sizes[i];
  buff_sizes[last]= sum;
  
  int n_buffers= t - f + 1;
  double buf_length= sum*elem_size;

  return (((double)buf_length/(n_buffers+1)) / IO_SIZE) * 2 * n_buffers + 
     buf_length * log(n_buffers)  / (TIME_FOR_COMPARE_ROWID * log(2.0));
}

/*
  Calculate cost of merging buffers into one in Unique::get, i.e. calculate
  how long (in terms of disk seeks) the two call
    merge_many_buffs(...); 
    merge_buffers(...); 
  will take.

  SYNOPSIS
    get_merge_many_buffs_cost()
      alloc         memory pool to use
      maxbuffer     # of full buffers.
      max_n_elems   # of elements in first maxbuffer buffers.
      last_n_elems  # of elements in last buffer.
      elem_size     size of buffer element.

  NOTES
    It is assumed that maxbuffer+1 buffers are merged, first maxbuffer buffers
    contain max_n_elems each, last buffer contains last_n_elems elements.

    The current implementation does a dumb simulation of merge_many_buffs
    actions.
  
  RETURN
    >=0  Cost of merge in disk seeks.
    <0   Out of memory.
*/
static double get_merge_many_buffs_cost(MEM_ROOT *alloc,
                                        uint maxbuffer, uint max_n_elems,
                                        uint last_n_elems, int elem_size)
{
  register int i;
  double total_cost= 0.0;
  int    lastbuff;
  uint*  buff_sizes;
  
  if (!(buff_sizes= (uint*)alloc_root(alloc, sizeof(uint) * (maxbuffer + 1))))
    return -1.0;
  for(i = 0; i < (int)maxbuffer; i++)
    buff_sizes[i]= max_n_elems;
  
  buff_sizes[maxbuffer]= last_n_elems;

  if (maxbuffer >= MERGEBUFF2)
  {
    /* Simulate merge_many_buff */
    while (maxbuffer >= MERGEBUFF2)
    {
      lastbuff=0;
      for (i = 0; i <= (int) maxbuffer - MERGEBUFF*3/2; i += MERGEBUFF)
        total_cost += get_merge_buffers_cost(buff_sizes, elem_size, 
                                             lastbuff++, i, i+MERGEBUFF-1);
      
      total_cost += get_merge_buffers_cost(buff_sizes, elem_size, 
                                           lastbuff++, i, maxbuffer);
      maxbuffer= (uint)lastbuff-1;
    }
  }
  
  /* Simulate final merge_buff call. */
  total_cost += get_merge_buffers_cost(buff_sizes, elem_size, 0, 0, 
                                       maxbuffer);
  return total_cost;
}


/*
  Calclulate cost of using Unique for processing nkeys elements of size 
  key_size using max_in_memory_size memory.
  
  RETURN
    >=0  Cost in disk seeks.
    <0   Out of memory.
  
  NOTES
    cost(using_unqiue) = 
      cost(create_trees) +  (see #1)
      cost(merge) +         (see #2)
      cost(read_result)     (see #3)

    1. Cost of trees creation
      For each Unique::put operation there will be 2*log2(n+1) elements
      comparisons, where n runs from 1 tree_size (we assume that all added
      elements are different). Together this gives:
    
      n_compares = 2*(log2(2) + log2(3) + ... + log2(N+1)) = 2*log2((N+1)!) =
  
      = 2*ln((N+1)!) / ln(2) = {using Stirling formula} = 

      = 2*( (N+1)*ln((N+1)/e) + (1/2)*ln(2*pi*(N+1)) / ln(2).

      then cost(tree_creation) = n_compares*ROWID_COMPARE_COST;

      Total cost of creating trees:
      (n_trees - 1)*max_size_tree_cost + non_max_size_tree_cost.
    
    2. Cost of merging.
      If only one tree is created by Unique no merging will be necessary.
      Otherwise, we model execution of merge_many_buff function and count
      #of merges. (The reason behind this is that number of buffers is small, 
      while size of buffers is big and we don't want to loose precision with 
      O(x)-style formula)
  
    3. If only one tree is created by Unique no disk io will happen.
      Otherwise, ceil(key_len*n_keys) disk seeks are necessary. We assume 
      these will be random seeks.
*/

double Unique::get_use_cost(MEM_ROOT *alloc, uint nkeys, uint key_size, 
                            ulong max_in_memory_size)
{
  ulong max_elements_in_tree;
  ulong last_tree_elems;
  int   n_full_trees; /* number of trees in unique - 1 */
  double result;
  
  max_elements_in_tree= max_in_memory_size / 
                        ALIGN_SIZE(sizeof(TREE_ELEMENT)+key_size);
  n_full_trees=    nkeys / max_elements_in_tree;
  last_tree_elems= nkeys % max_elements_in_tree;
  
  /* Calculate cost of creating trees */
  result= log2_n_fact(last_tree_elems);
  if (n_full_trees)
    result+= n_full_trees * log2_n_fact(max_elements_in_tree);
  result /= TIME_FOR_COMPARE_ROWID;

  DBUG_PRINT("info",("unique trees sizes: %u=%u*%lu + %lu", nkeys,
                     n_full_trees, n_full_trees?max_elements_in_tree:0,
                     last_tree_elems));

  if (!n_full_trees)
    return result;
  
  /* 
    There is more then one tree and merging is necessary.
    First, add cost of writing all trees to disk. 
  */
  result += n_full_trees * ceil(key_size*max_elements_in_tree / IO_SIZE);
  result += ceil(key_size*last_tree_elems / IO_SIZE);

  /* Cost of merge */
  double merge_cost= get_merge_many_buffs_cost(alloc, n_full_trees,
                                               max_elements_in_tree,
                                               last_tree_elems, key_size);
  if (merge_cost < 0.0)
    return merge_cost;

  result += merge_cost;
  /* 
    Add cost of reading the resulting sequence, assuming there were no 
    duplicate elements.
  */
  result += ceil((double)key_size*nkeys/IO_SIZE);

  return result;
}

Unique::~Unique()
{
  close_cached_file(&file);
  delete_tree(&tree);
  delete_dynamic(&file_ptrs);
}


    /* Write tree to disk; clear tree */    
bool Unique::flush()
{
  BUFFPEK file_ptr;
  elements+= tree.elements_in_tree;
  file_ptr.count=tree.elements_in_tree;
  file_ptr.file_pos=my_b_tell(&file);
  if (tree_walk(&tree, (tree_walk_action) unique_write_to_file,
		(void*) this, left_root_right) ||
      insert_dynamic(&file_ptrs, (gptr) &file_ptr))
    return 1;
  delete_tree(&tree);
  return 0;
}


/*
  Modify the TABLE element so that when one calls init_records()
  the rows will be read in priority order.
*/

bool Unique::get(TABLE *table)
{
  SORTPARAM sort_param;
  table->sort.found_records=elements+tree.elements_in_tree;

  if (my_b_tell(&file) == 0)
  {
    /* Whole tree is in memory;  Don't use disk if you don't need to */
    if ((record_pointers=table->sort.record_pointers= (byte*)
	 my_malloc(size * tree.elements_in_tree, MYF(0))))
    {
      (void) tree_walk(&tree, (tree_walk_action) unique_write_to_ptrs,
		       this, left_root_right);
      return 0;
    }
  }
  /* Not enough memory; Save the result to file */
  if (flush())
    return 1;

  IO_CACHE *outfile=table->sort.io_cache;
  BUFFPEK *file_ptr= (BUFFPEK*) file_ptrs.buffer;
  uint maxbuffer= file_ptrs.elements - 1;
  uchar *sort_buffer;
  my_off_t save_pos;
  bool error=1;

      /* Open cached file if it isn't open */
  outfile=table->sort.io_cache=(IO_CACHE*) my_malloc(sizeof(IO_CACHE), 
                                MYF(MY_ZEROFILL));

  if (!outfile || ! my_b_inited(outfile) &&
      open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER,
		       MYF(MY_WME)))
    return 1;
  reinit_io_cache(outfile,WRITE_CACHE,0L,0,0);

  bzero((char*) &sort_param,sizeof(sort_param));
  sort_param.max_rows= elements;
  sort_param.sort_form=table;
  sort_param.rec_length= sort_param.sort_length=sort_param.ref_length=
    size;
  sort_param.keys= max_in_memory_size / sort_param.sort_length;
  sort_param.not_killable=1;

  if (!(sort_buffer=(uchar*) my_malloc((sort_param.keys+1) * 
				       sort_param.sort_length,
				       MYF(0))))
    return 1;
  sort_param.unique_buff= sort_buffer+(sort_param.keys*
				       sort_param.sort_length);

  /* Merge the buffers to one file, removing duplicates */
  if (merge_many_buff(&sort_param,sort_buffer,file_ptr,&maxbuffer,&file))
    goto err;
  if (flush_io_cache(&file) ||
      reinit_io_cache(&file,READ_CACHE,0L,0,0))
    goto err;
  if (merge_buffers(&sort_param, &file, outfile, sort_buffer, file_ptr,
		    file_ptr, file_ptr+maxbuffer,0))
    goto err;                                                                 
  error=0;
err:
  x_free((gptr) sort_buffer);
  if (flush_io_cache(outfile))
    error=1;

  /* Setup io_cache for reading */
  save_pos=outfile->pos_in_file;
  if (reinit_io_cache(outfile,READ_CACHE,0L,0,0))
    error=1;
  outfile->end_of_file=save_pos;
  return error;
}