merge_many_buff.h

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/* Copyright (c) 2016, 2025, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef MERGE_MANY_BUFF_INCLUDED
#define MERGE_MANY_BUFF_INCLUDED
 
#include <algorithm>
 
#include "my_dbug.h"
#include "my_sys.h"        // open_cached_file
#include "sql/mysqld.h"    // mysql_tmpdir
#include "sql/sql_base.h"  // TEMP_PREFIX
#include "sql/sql_sort.h"  // Sort_buffer
 
class THD;
 
/**
  Merges buffers to make < MERGEBUFF2 buffers.
 
  @param thd          thread context
  @param param        Sort parameters.
  @param sort_buffer  The main memory buffer.
  @param chunk_array  Array of chunk descriptors to merge.
  @param [out] p_num_chunks The number of chunks left in the output file.
  @param [out] t_file Where to store the result.
 
  @returns   false if success, true if error
*/
 
template <typename Merge_param>
bool merge_many_buff(THD *thd, Merge_param *param, Sort_buffer sort_buffer,
                     Merge_chunk_array chunk_array, size_t *p_num_chunks,
                     IO_CACHE *t_file) {
  IO_CACHE t_file2;
  DBUG_TRACE;
 
  size_t num_chunks = chunk_array.size();
  *p_num_chunks = num_chunks;
 
  if (num_chunks <= MERGEBUFF2) return false; /* purecov: inspected */
 
  if (flush_io_cache(t_file) ||
      open_cached_file(&t_file2, mysql_tmpdir, TEMP_PREFIX, DISK_BUFFER_SIZE,
                       MYF(MY_WME)))
    return true; /* purecov: inspected */
 
  IO_CACHE *from_file = t_file;
  IO_CACHE *to_file = &t_file2;
 
  while (num_chunks > MERGEBUFF2) {
    if (reinit_io_cache(from_file, READ_CACHE, 0L, false, false)) goto cleanup;
    if (reinit_io_cache(to_file, WRITE_CACHE, 0L, false, false)) goto cleanup;
    Merge_chunk *last_chunk = chunk_array.begin();
    uint i;
    for (i = 0; i < num_chunks - MERGEBUFF * 3U / 2U; i += MERGEBUFF) {
      if (merge_buffers(thd, param, from_file, to_file, sort_buffer,
                        last_chunk++,
                        Merge_chunk_array(&chunk_array[i], MERGEBUFF),
                        /*include_keys=*/true))
        goto cleanup;
    }
    if (merge_buffers(thd, param, from_file, to_file, sort_buffer, last_chunk++,
                      Merge_chunk_array(&chunk_array[i], num_chunks - i),
                      /*include_keys=*/true))
      break;                            /* purecov: inspected */
    if (flush_io_cache(to_file)) break; /* purecov: inspected */
 
    std::swap(from_file, to_file);
    setup_io_cache(from_file);
    setup_io_cache(to_file);
    num_chunks = last_chunk - chunk_array.begin();
  }
cleanup:
  close_cached_file(to_file);  // This holds old result
  if (to_file == t_file) {
    *t_file = t_file2;  // Copy result file
    setup_io_cache(t_file);
  }
 
  *p_num_chunks = num_chunks;
  return num_chunks > MERGEBUFF2; /* Return true if interrupted */
} /* merge_many_buff */
 
#endif  // MERGE_MANY_BUFF_INCLUDED