Monday, August 24, 2015

Tuning (and understanding) table_cache in mySQL

I ran the excellent MySQL performance tuning script and started to work through the suggestions. One I ran into was





TABLE CACHE
Current table_cache value = 4096 tables You have a total
of 1073 tables. You have 3900 open tables. Current table_cache hit
rate is 2%, while 95% of your table cache is in use. You should
probably increase your table_cache




I started to read up on the table_cache but found the MySQL documentation quite lacking. They do say to increase the table_cache, "if you have the memory". Unfortunately the table_cache variable is defined as "The number of open tables for all threads."




How will the memory used by MySQL change, if I increase this variable? What is a good value, to set it to?

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