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Re: Queries slow down daily, optimizing helps -> why?
Posted by: aftab khan
Date: February 26, 2009 09:56AM

your query requires an index scan, which pushes out of the cache all the index blocks corresponding to valuable high-level B-tree nodes. thats why you observe slow and fast behavior.

try

SET GLOBAL key_cache_division_limit=25;

if possible use different cache for these tables...

mysql> SET GLOBAL hot_cache.key_buffer_size=128*1024;
Query OK, 0 rows affected (0.00 sec)

mysql> CACHE INDEX `person` , `user` IN hot_cache;
+-------------+--------------------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+-------------+--------------------+----------+----------+
| test.person | assign_to_keycache | status | OK |
| test.user | assign_to_keycache | status | OK |
+-------------+--------------------+----------+----------+
2 rows in set (0.00 sec)

mysql> SET GLOBAL hot_cache.key_buffer_size=128*1024*1024;
Query OK, 0 rows affected (0.00 sec)

mysql> CACHE INDEX `person` , `user` IN hot_cache;
+-------------+--------------------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+-------------+--------------------+----------+----------+
| test.person | assign_to_keycache | status | OK |
| test.user | assign_to_keycache | status | OK |
+-------------+--------------------+----------+----------+
2 rows in set (0.00 sec)

mysql> LOAD INDEX INTO CACHE `person` , `user` IGNORE LEAVES;
+-------------+--------------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+-------------+--------------+----------+----------+
| test.person | preload_keys | status | OK |
| test.user | preload_keys | status | OK |
+-------------+--------------+----------+----------+
2 rows in set (0.00 sec)

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March 18, 2009 03:58AM
Re: Queries slow down daily, optimizing helps -> why?
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February 26, 2009 09:56AM


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