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Re: [Commits] Rev 3138: Early check of subquery cache hit rate added to limit its performance impact in the worst case. in file:///home/bell/maria/bzr/work-maria-5.3-scache_impact/

To: Timour Katchaounov <timour@xxxxxxxxxxxxxxxx>
From: Oleksandr Byelkin <sanja@xxxxxxxxxxxx>
Date: Mon, 01 Aug 2011 13:27:02 +0300
Cc: maria-developers@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4E3651F8.8000700@montyprogram.com>
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110617 Thunderbird/3.1.11

Hi!

01.08.2011 10:12, Timour Katchaounov пишет:

Sanja,

Could you explain why these new constants are defines,
and not declared const variables:

=== modified file 'sql/sql_expression_cache.cc'
--- a/sql/sql_expression_cache.cc    2011-07-28 14:10:29 +0000
+++ b/sql/sql_expression_cache.cc    2011-08-01 06:34:55 +0000
@@ -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_EARLY_CHECK 200


All of these are potentially possible to tune, why make them
compile-time defines?

Heh, that is what I wanted to discuss. On one hand too many parametersis bad on other hand too simple is not good also...


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