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Re: MySQL read/Write very slow in a table because of long blob columns
Posted by: Øystein Grøvlen
Date: November 25, 2015 02:04AM

Hi,

Whether indexing and/or partitioning will help, depends greatly on your usage pattern. It is not clear from what you write whether the limiting factor is the amount of inserts/updates of blob columns or how much data needs to be accessed in order to identify a set of interesting rows.

Difficult to say why indexes does not improve performance without seeing your queries, but in general, the WHERE clause of your queries need to contain conditions on the indexed columns for an index to be of use. The expressions referring to a column may also be written in a way that an index is not possible to use (e.g., the column is a parameter to a function), or the order of columns in a multi-column index is not adequate for your query.

Similarly, for partitioning to help, your WHERE clause needs to have conditions on columns of the partition key so that MySQL can limit what partitions to access.

In other words, in order to give you any specific advice, we will need to know more about the SQL statements you want to improve.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway

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