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Search Results for: mysql index cardinality

Performance gotcha of MySQL memory tables

One performance gotcha with MEMORY tables you might know about comes from the fact it is the only MySQL storage engine which defaults to HASH index type by default, instead of BTREE which makes indexes …


MySQL automatic data truncation can backfire

I had a fun case today. There is set of cache tables which cache certain content in MyISAM tables and queries for these tables such as:

The “key” is CRC32 of the real key …


MySQL Crash Recovery

MySQL is known for its stability but as any other application it has bugs so it may crash sometime. Also operation system may be flawed, hardware has problems or simply power can go down which …


MySQL EXPLAIN limits and errors.

Running EXPLAIN for problematic queries is very powerful tool for MySQL Performance optimization. If you’ve been using this tool a lot you probably noticed it is not always provide adequate information. Here is list of …


The ARCHIVE Storage Engine – does it do what you expect?

Sometimes there is a need for keeping large amounts of old, rarely used data without investing too much on expensive storage. Very often such data doesn’t need to be updated anymore, or the intent is …


Percona Toolkit 2.1.10 is now available

Percona is glad to announce the release of Percona Toolkit 2.1.10 on July 18th, 2013 (Downloads are available here). Bugs Fixed: Unfortunately, the relatively new –utc option for pt-heart was still broken because “MySQL interprets date as …


Percona Toolkit 2.2.4 is now available

Percona is glad to announce the release of Percona Toolkit 2.2.4 on July 17th, 2013 (Downloads are available here and from the Percona Software Repositories). New Features: pt-query-digest –output json includes query examples as of v2.2.3. Some people might …


When EXPLAIN estimates can go wrong!

I have been working with a few customer cases and one interesting case popped up. The customer was facing a peculiar problem where the rows column in the EXPLAIN output of the query was totally …


When Does InnoDB Update Table Statistics? (And When It Can Bite)

An InnoDB table statistics is used for JOIN optimizations and helping the MySQL optimizer choose the appropriate index for a query. If a table’s statistics or index cardinality becomes outdated, you might see queries which …