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Re: Slow query
Posted by: Manu Swami
Date: April 25, 2015 02:41AM

I have seen an interesting difference as well. The storage_engine changed to InnoDB from MyISAM. That is why it is showing block Nested loop in EXPLAIN plan. If I turn off block nested loop then EXPLAIN will be similar to the earlier server but still it doesn't improve performance.

I have also checked that the column imsiid of imsi_ne table has low cardinality, may be because of low cardinality the optimizer is not selecting index in SQL explain plan. To remedy this I have analyzed the imsi_ne table, seems “analyze table” doesn’t work well with InnoDB engine because InnoDB has automatic optimization technique in place. So the column still has zero cardinality.

May be it has to do with MyISAM to InnoDB change. May be there is some default value from InnoDB is SET which need to be UNSET or something like this. I am just guessing such things not sure at all.

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