Things that Kill MySQL Performance

Paul — Thu, 05 Nov 2009 01:59:19 +0000

Failing to plan for scaling out, scaling up
Not using EXPLAIN (learn from your mistakes)
Using the wrong data types (hint: use smallest fixed-size)
Using persistent connections in PHP (leads to zombie processes)
Using a heavy DB abstraction layer (hint: use PDO or custom)
Using the wrong storage engine (MEMORY, ARCHIVE, InnoDB, etc.)
Using indexes improperly (hint: select in the order of the index; hint: keep primary key small)
Issuing SQL queries that can’t be cached easily; having too large of a query cache
Using stored procedures when prepared statements are better
Using functions on indexed columns in the WHERE clause
Not indexing important columns; having redundant indexes
Using sub-queries when joins would be better
Issuing avoidable deep scans
Doing SELECT COUNT(*) without WHERE on InnoDB table.
Failing to profile/benchmark your SQL
Not using AUTO_INCREMENT if applicable
Not using ON DUPLICATE KEY UPDATE (1 query vs 2)

Reference:

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