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Subquery cache going on disk management fix: Do not go on disk if hit rate is not good.

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sql/sql_expression_cache.cc:
  Do not go on disk if hit rate is not good.
  Local hit/miss counters added.
sql/sql_expression_cache.h:
  Local hit/miss counters added.
This commit is contained in:
unknown 2011-07-28 17:10:29 +03:00
parent 668eb2b55e
commit cfa08e8dad
2 changed files with 44 additions and 6 deletions
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48
sql/sql_expression_cache.cc
View File

@ -16,6 +16,17 @@
#include "mysql_priv.h"
#include "sql_select.h"
/**
Minimum hit ration to proceed on disk if in memory table overflowed.
hit_rate = hit / (miss + hit);
*/
#define EXPCACHE_MIN_HIT_RATE_FOR_DISK_TABLE 0.7
/**
Minimum hit ratio to keep in memory table (do not switch cache off)
hit_rate = hit / (miss + hit);
*/
#define EXPCACHE_MIN_HIT_RATE_FOR_MEM_TABLE 0.2
/*
Expression cache is used only for caching subqueries now, so its statistic
variables we call subquery_cache*.
@ -26,7 +37,7 @@ Expression_cache_tmptable::Expression_cache_tmptable(THD *thd,
List<Item> &dependants,
Item *value)
:cache_table(NULL), table_thd(thd), items(dependants), val(value),
inited (0)
hit(0), miss(0), inited (0)
{
DBUG_ENTER("Expression_cache_tmptable::Expression_cache_tmptable");
DBUG_VOID_RETURN;
@ -180,10 +191,12 @@ Expression_cache::result Expression_cache_tmptable::check_value(Item **value)
if (res)
{
subquery_cache_miss++;
miss++;
DBUG_RETURN(MISS);
}
subquery_cache_hit++;
hit++;
*value= cached_result;
DBUG_RETURN(Expression_cache::HIT);
}
@ -224,12 +237,35 @@ my_bool Expression_cache_tmptable::put_value(Item *value)
if ((error= cache_table->file->ha_write_tmp_row(cache_table->record[0])))
{
/* create_myisam_from_heap will generate error if needed */
if (cache_table->file->is_fatal_error(error, HA_CHECK_DUP) &&
create_internal_tmp_table_from_heap(table_thd, cache_table,
cache_table_param.start_recinfo,
&cache_table_param.recinfo,
error, 1))
if (cache_table->file->is_fatal_error(error, HA_CHECK_DUP))
goto err;
else
{
double hit_rate= ((double)hit / ((double)hit + miss));
DBUG_ASSERT(miss > 0);
if (hit_rate < EXPCACHE_MIN_HIT_RATE_FOR_MEM_TABLE)
{
DBUG_PRINT("info", ("hit rate is not so good to keep the cache"));
free_tmp_table(table_thd, cache_table);
cache_table= NULL;
DBUG_RETURN(FALSE);
}
else if (hit_rate < EXPCACHE_MIN_HIT_RATE_FOR_DISK_TABLE)
{
DBUG_PRINT("info", ("hit rate is not so good to go to disk"));
if (cache_table->file->ha_delete_all_rows() ||
cache_table->file->ha_write_tmp_row(cache_table->record[0]))
goto err;
}
else
{
if (create_internal_tmp_table_from_heap(table_thd, cache_table,
cache_table_param.start_recinfo,
&cache_table_param.recinfo,
error, 1))
goto err;
}
}
}
cache_table->status= 0; /* cache_table->record contains an existed record */
ref.has_record= TRUE; /* the same as above */

2
sql/sql_expression_cache.h
View File

@ -85,6 +85,8 @@ private:
List<Item> &items;
/* Value Item example */
Item *val;
/* hit/miss counters */
uint hit, miss;
/* Set on if the object has been succesfully initialized with init() */
bool inited;
};