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Introduced optimizer switch flag 'optimize_join_buffer_size'.

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When this flag is 'off' the size of the used join buffer 
is taken directly from the system variable 'join_buffer_size'.
When this flag is 'on' then the size of the buffer depends
on the estimated number of rows in the partial join whose
records are to be stored in the buffer.
By default this flag is set 'on'.
This commit is contained in:
Igor Babaev
2011-02-04 19:06:35 -08:00
parent 7e20687212
commit 4b24105df8
5 changed files with 62 additions and 43 deletions
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47
sql/sql_join_cache.cc
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@ -747,6 +747,7 @@ ulong JOIN_CACHE::get_min_join_buffer_size()
avg_aux_buffer_incr= add_sz/min_records;
min_sz+= add_sz;
min_sz+= pack_length_with_blob_ptrs;
set_if_bigger(min_sz, 1);
min_buff_size= min_sz;
}
return min_buff_size;
@ -759,16 +760,20 @@ ulong JOIN_CACHE::get_min_join_buffer_size()
SYNOPSIS
get_max_join_buffer_size()
optimize_buff_size FALSE <-> do not take more memory than needed for
the estimated number of records in the partial join
DESCRIPTION
At the first its invocation for the cache the function calculates the
maximum possible size of join buffer for the cache. This value does not
exceed the estimate of the number of records 'max_records' in the partial
join that joins tables from the first one through join_tab. This value
is also capped off by the value of join_tab->join_buffer_size_limit, if it
has been set a to non-zero value, and by the value of the system parameter
join_buffer_size - otherwise. After the calculation of the interesting size
the function saves the value in the field 'max_buff_size' in order to use
it directly at the next invocations of the function.
maximum possible size of join buffer for the cache. If the parameter
optimize_buff_size true then this value does not exceed the size of the
space needed for the estimated number of records 'max_records' in the
partial join that joins tables from the first one through join_tab. This
value is also capped off by the value of join_tab->join_buffer_size_limit,
if it has been set a to non-zero value, and by the value of the system
parameter join_buffer_size - otherwise. After the calculation of the
interesting size the function saves the value in the field 'max_buff_size'
in order to use it directly at the next invocations of the function.
NOTES
Currently the value of join_tab->join_buffer_size_limit is initialized
@ -778,7 +783,7 @@ ulong JOIN_CACHE::get_min_join_buffer_size()
The maximum possible size of the join buffer of this cache
*/
ulong JOIN_CACHE::get_max_join_buffer_size()
ulong JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size)
{
if (!max_buff_size)
{
@ -795,12 +800,17 @@ ulong JOIN_CACHE::get_max_join_buffer_size()
ulong limit_sz= join->thd->variables.join_buff_size;
if (join_tab->join_buffer_size_limit)
set_if_smaller(limit_sz, join_tab->join_buffer_size_limit);
if (limit_sz / max_records > space_per_record)
max_sz= space_per_record * max_records;
else
if (!optimize_buff_size)
max_sz= limit_sz;
max_sz+= pack_length_with_blob_ptrs;
set_if_smaller(max_sz, limit_sz);
else
{
if (limit_sz / max_records > space_per_record)
max_sz= space_per_record * max_records;
else
max_sz= limit_sz;
max_sz+= pack_length_with_blob_ptrs;
set_if_smaller(max_sz, limit_sz);
}
set_if_bigger(max_sz, min_sz);
max_buff_size= max_sz;
}
@ -843,6 +853,8 @@ int JOIN_CACHE::alloc_buffer()
ulonglong curr_min_buff_space_sz= 0;
ulonglong join_buff_space_limit=
join->thd->variables.join_buff_space_limit;
bool optimize_buff_size=
optimizer_flag(join->thd, OPTIMIZER_SWITCH_OPTIMIZE_JOIN_BUFFER_SIZE);
double partial_join_cardinality= (join_tab-1)->get_partial_join_cardinality();
buff= NULL;
min_buff_size= 0;
@ -852,7 +864,7 @@ int JOIN_CACHE::alloc_buffer()
(ulonglong) partial_join_cardinality : join_buff_space_limit;
set_if_bigger(max_records, 10);
min_buff_size= get_min_join_buffer_size();
buff_size= get_max_join_buffer_size();
buff_size= get_max_join_buffer_size(optimize_buff_size);
for (tab= join->join_tab+join->const_tables; tab <= join_tab; tab++)
{
cache= tab->cache;
@ -865,8 +877,9 @@ int JOIN_CACHE::alloc_buffer()
if (curr_min_buff_space_sz > join_buff_space_limit ||
(curr_buff_space_sz > join_buff_space_limit &&
join->shrink_join_buffers(join_tab, curr_buff_space_sz,
join_buff_space_limit)))
(!optimize_buff_size ||
join->shrink_join_buffers(join_tab, curr_buff_space_sz,
join_buff_space_limit))))
goto fail;
for (ulong buff_size_decr= (buff_size-min_buff_size)/4 + 1; ; )