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POSQL_NO_CACHE does not work
 

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  1. POSQL_NO_CACHE does not work
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    <p>The first time I run this sql, needs 39 seconds,when I run again and increase SQL_NO_CACHE,does not seem to take effect:</p> <pre><code>mysql&gt; select count(*) from `deal_expired` where `site`=8&amp;&amp;`area`=122 &amp;&amp; endtime&lt;1310444996056; +----------+ | count(*) | +----------+ | 497 | +----------+ 1 row in set (39.55 sec) mysql&gt; select SQL_NO_CACHE count(*) from `deal_expired` where `site`=8&amp;&amp;`area`= 122 &amp;&amp; endtime&lt;1310444996056; +----------+ | count(*) | +----------+ | 497 | +----------+ 1 row in set (0.16 sec) </code></pre> <p>I tried a variety of methods, <a href="http://www.issociate.de/board/post/493985/SQL_NO_CACHE.html" rel="noreferrer">here</a></p> <p>and even restart the mysql server or change table name, but I still can not let 39 seconds run this SQL</p> <p>I replaced another SQL, and an increase in the first run on SQL_NO_CACHE, the problem is the same:</p> <pre><code>mysql&gt; select SQL_NO_CACHE count(*) from `deal_expired` where `site`=25&amp;&amp;`area`= 134 &amp;&amp; endtime&lt;1310483196227; +----------+ | count(*) | +----------+ | 315 | +----------+ 1 row in set (2.17 sec) mysql&gt; select SQL_NO_CACHE count(*) from `deal_expired` where `site`=25&amp;&amp;`area`= 134 &amp;&amp; endtime&lt;1310483196227; +----------+ | count(*) | +----------+ | 315 | +----------+ 1 row in set (0.01 sec) </code></pre> <p>What is the reason? How can I get the same SQL run-time?</p> <p>I want to find a way to optimize this SQL to perform 39 seconds</p> <p>BTW: <code>RESET QUERY CACHE</code> <code>FLUSH QUERY CACHE</code> <code>FLUSH TABLES</code> <code>SET SESSION query_cache_type=off</code> does not work</p> <p>mysql state cache has been closed:</p> <pre><code>mysql&gt; SHOW STATUS LIKE "Qcache%"; +-------------------------+-------+ | Variable_name | Value | +-------------------------+-------+ | Qcache_free_blocks | 0 | | Qcache_free_memory | 0 | | Qcache_hits | 0 | | Qcache_inserts | 0 | | Qcache_lowmem_prunes | 0 | | Qcache_not_cached | 0 | | Qcache_queries_in_cache | 0 | | Qcache_total_blocks | 0 | +-------------------------+-------+ 8 rows in set (0.04 sec) mysql&gt; select count(*) from `deal_expired` where `site`=25&amp;&amp;`area`=134 &amp;&amp; endtime&lt;1310 483196227; +----------+ | count(*) | +----------+ | 315 | +----------+ 1 row in set (0.01 sec) mysql&gt; SHOW STATUS LIKE "Qcache%"; +-------------------------+-------+ | Variable_name | Value | +-------------------------+-------+ | Qcache_free_blocks | 0 | | Qcache_free_memory | 0 | | Qcache_hits | 0 | | Qcache_inserts | 0 | | Qcache_lowmem_prunes | 0 | | Qcache_not_cached | 0 | | Qcache_queries_in_cache | 0 | | Qcache_total_blocks | 0 | +-------------------------+-------+ 8 rows in set (0.00 sec) </code></pre> <hr> <p>explan this SQL,used site+endtime composite index(named site_endtime):</p> <pre><code>mysql&gt; explain select count(*) from `deal_expired` where `site`=8&amp;&amp;`area`=122 &amp;&amp; endti me&lt;1310444996056; +--------+------+-------------------------------+--------------+---------+------ -+------+-------------+ | table | type | possible_keys | key | key_len | ref | rows | Extra | +--------+------+-------------------------------+--------------+---------+------ -+------+-------------+ | deal_expired | ref | name,url,endtime,site_endtime | site_endtime | 4 | const | 353 | Using where | +--------+------+-------------------------------+--------------+---------+------ -+------+-------------+ 1 row in set (0.00 sec) </code></pre>
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    1. CODo you use **composite** index for this query?
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    2. CO@Karolis has a site+endtime (named `site_endtime`) composite index
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    3. COI don't know anything about your particular database, but it seems that it would be a good idea to create another composite index (site+area+endtime). MySql will read less rows, so it should become faster.
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