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Early check of subquery cache hit rate added to limit its performance impact in the worst case.

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sql/sql_expression_cache.cc:
  Early check of subquery cache hit rate added to limit its performance impact in the worst case.
  Disabling cache moved to method.
sql/sql_expression_cache.h:
  Disabling cache moved to method.
This commit is contained in:
unknown 2011-08-12 13:54:41 +03:00
parent fede2ee7f1
commit 52e70226bc
2 changed files with 30 additions and 9 deletions
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38
sql/sql_expression_cache.cc
View File

@ -26,6 +26,11 @@
hit_rate = hit / (miss + hit);
*/
#define EXPCACHE_MIN_HIT_RATE_FOR_MEM_TABLE 0.2
/**
Number of cache miss to check hit ratio (maximum cache performance
impact in the case when the cache is not applicable)
*/
#define EXPCACHE_CHECK_HIT_RATIO_AFTER 200
/*
Expression cache is used only for caching subqueries now, so its statistic
@ -44,6 +49,17 @@ Expression_cache_tmptable::Expression_cache_tmptable(THD *thd,
};
/**
Disable cache
*/
void Expression_cache_tmptable::disable_cache()
{
free_tmp_table(table_thd, cache_table);
cache_table= NULL;
}
/**
Field enumerator for TABLE::add_tmp_key
@ -148,9 +164,7 @@ void Expression_cache_tmptable::init()
DBUG_VOID_RETURN;
error:
/* switch off cache */
free_tmp_table(table_thd, cache_table);
cache_table= NULL;
disable_cache();
DBUG_VOID_RETURN;
}
@ -162,7 +176,7 @@ Expression_cache_tmptable::~Expression_cache_tmptable()
statistic_add(subquery_cache_hit, hit, &LOCK_status);
if (cache_table)
free_tmp_table(table_thd, cache_table);
disable_cache();
}
@ -195,7 +209,15 @@ Expression_cache::result Expression_cache_tmptable::check_value(Item **value)
if (res)
{
miss++;
if (((++miss) == EXPCACHE_CHECK_HIT_RATIO_AFTER) &&
((double)hit / ((double)hit + miss)) <
EXPCACHE_MIN_HIT_RATE_FOR_MEM_TABLE)
{
DBUG_PRINT("info",
("Early check: hit rate is not so good to keep the cache"));
disable_cache();
}
DBUG_RETURN(MISS);
}
@ -249,8 +271,7 @@ my_bool Expression_cache_tmptable::put_value(Item *value)
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;
disable_cache();
DBUG_RETURN(FALSE);
}
else if (hit_rate < EXPCACHE_MIN_HIT_RATE_FOR_DISK_TABLE)
@ -277,8 +298,7 @@ my_bool Expression_cache_tmptable::put_value(Item *value)
DBUG_RETURN(FALSE);
err:
free_tmp_table(table_thd, cache_table);
cache_table= NULL;
disable_cache();
DBUG_RETURN(TRUE);
}

1
sql/sql_expression_cache.h
View File

@ -70,6 +70,7 @@ public:
void init();
private:
void disable_cache();
/* tmp table parameters */
TMP_TABLE_PARAM cache_table_param;