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/* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
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; version 2 of the License.
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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
#include "mariadb.h"
#include "filesort_utils.h"
#include "sql_const.h"
#include "sql_sort.h"
#include "table.h"
namespace {
/**
A local helper function. See comments for get_merge_buffers_cost().
*/
double get_merge_cost(ha_rows num_elements, ha_rows num_buffers, uint elem_size)
{
return
2.0 * ((double) num_elements * elem_size) / IO_SIZE
+ (double) num_elements * log((double) num_buffers) /
(TIME_FOR_COMPARE_ROWID * M_LN2);
}
}
/**
This is a simplified, and faster version of @see get_merge_many_buffs_cost().
We calculate the cost of merging buffers, by simulating the actions
of @see merge_many_buff. For explanations of formulas below,
see comments for get_merge_buffers_cost().
TODO: Use this function for Unique::get_use_cost().
*/
double get_merge_many_buffs_cost_fast(ha_rows num_rows,
ha_rows num_keys_per_buffer,
uint elem_size)
{
ha_rows num_buffers= num_rows / num_keys_per_buffer;
ha_rows last_n_elems= num_rows % num_keys_per_buffer;
double total_cost;
// Calculate CPU cost of sorting buffers.
total_cost=
( num_buffers * num_keys_per_buffer * log(1.0 + num_keys_per_buffer) +
last_n_elems * log(1.0 + last_n_elems) )
/ TIME_FOR_COMPARE_ROWID;
// Simulate behavior of merge_many_buff().
while (num_buffers >= MERGEBUFF2)
{
// Calculate # of calls to merge_buffers().
const ha_rows loop_limit= num_buffers - MERGEBUFF*3/2;
const ha_rows num_merge_calls= 1 + loop_limit/MERGEBUFF;
const ha_rows num_remaining_buffs=
num_buffers - num_merge_calls * MERGEBUFF;
// Cost of merge sort 'num_merge_calls'.
total_cost+=
num_merge_calls *
get_merge_cost(num_keys_per_buffer * MERGEBUFF, MERGEBUFF, elem_size);
// # of records in remaining buffers.
last_n_elems+= num_remaining_buffs * num_keys_per_buffer;
// Cost of merge sort of remaining buffers.
total_cost+=
get_merge_cost(last_n_elems, 1 + num_remaining_buffs, elem_size);
num_buffers= num_merge_calls;
num_keys_per_buffer*= MERGEBUFF;
}
// Simulate final merge_buff call.
last_n_elems+= num_keys_per_buffer * num_buffers;
total_cost+= get_merge_cost(last_n_elems, 1 + num_buffers, elem_size);
return total_cost;
}
/*
alloc_sort_buffer()
Allocate buffer for sorting keys.
Try to reuse old buffer if possible.
@return
0 Error
# Pointer to allocated buffer
*/
uchar *Filesort_buffer::alloc_sort_buffer(uint num_records,
uint record_length)
{
size_t buff_size;
DBUG_ENTER("alloc_sort_buffer");
DBUG_EXECUTE_IF("alloc_sort_buffer_fail",
DBUG_SET("+d,simulate_out_of_memory"););
buff_size= ALIGN_SIZE(num_records * (record_length + sizeof(uchar*)));
/*
The minimum memory required should be each merge buffer can hold atmost
one key.
TODO varun: move this to the place where min_sort_memory is used.
*/
set_if_bigger(buff_size,
ALIGN_SIZE((record_length +sizeof(uchar*)) * MERGEBUFF2));
if (m_rawmem)
{
/*
Reuse old buffer if exists and is large enough
Note that we don't make the buffer smaller, as we want to be
prepared for next subquery iteration.
*/
if (buff_size > m_size_in_bytes)
{
/*
Better to free and alloc than realloc as we don't have to remember
the old values
*/
my_free(m_rawmem);
if (!(m_rawmem= (uchar*) my_malloc(buff_size, MYF(MY_THREAD_SPECIFIC))))
{
m_size_in_bytes= 0;
DBUG_RETURN(0);
}
}
}
else
{
if (!(m_rawmem= (uchar*) my_malloc(buff_size, MYF(MY_THREAD_SPECIFIC))))
{
m_size_in_bytes= 0;
DBUG_RETURN(0);
}
}
m_size_in_bytes= buff_size;
m_record_pointers= reinterpret_cast<uchar**>(m_rawmem) +
((m_size_in_bytes / sizeof(uchar*)) - 1);
m_num_records= num_records;
m_record_length= record_length;
m_idx= 0;
DBUG_RETURN(m_rawmem);
}
void Filesort_buffer::free_sort_buffer()
{
my_free(m_rawmem);
*this= Filesort_buffer();
}
void Filesort_buffer::sort_buffer(const Sort_param *param, uint count)
{
size_t size= param->sort_length;
m_sort_keys= get_sort_keys();
if (count <= 1 || size == 0)
return;
// dont reverse for PQ, it is already done
if (!param->using_pq)
reverse_record_pointers();
uchar **buffer= NULL;
if (radixsort_is_appliccable(count, param->sort_length) &&
(buffer= (uchar**) my_malloc(count*sizeof(char*),
MYF(MY_THREAD_SPECIFIC))))
{
radixsort_for_str_ptr(m_sort_keys, count, param->sort_length, buffer);
my_free(buffer);
return;
}
my_qsort2(m_sort_keys, count, sizeof(uchar*), get_ptr_compare(size), &size);
}
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