Re: [Maria-developers] [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/

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 parameters is bad on other hand too simple is not good also... [skip]