Emergency

Tag Archives: Bugs

How much overhead is caused by on disk temporary tables

As you might know while running GROUP BY and some other kinds of queries MySQL needs to create temporary tables, which can be created in memory, using MEMORY storage engine or can be created on …

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MySQL VIEW as performance troublemaker

I start to see applications being built utilizing VIEWs functionality which appeared in MySQL 5.0 and quite frequently VIEWs are used to help in writing the queries – to keep queries simple without really thinking …

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Query_cache and column level privileges

Recently we were puzzled by question how query_cache works with column level privileges. The question was appeared as we discovered function query_cache_send_result_to_client is called before real parsing of query, so at the moment of execution …

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More Gotchas with MySQL 5.0

Working on large upgrade of MySQL 4.1 running Innodb to MySQL 5.0 and doing oprofile analyzes we found very interesting issue of buf_get_latched_pages_number being responsible for most CPU usage. It did not look right. The …

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MySQL 5.0 Community Edition Regression

It is true you might be better of being unaware about problems, because in this case you might not run into them Just couple of days ago Kaj Arno told me there are issues reported …

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Using CHAR keys for joins, how much is the overhead ?

I prefer to use Integers for joins whenever possible and today I worked with client which used character keys, in my opinion without a big need. I told them this is suboptimal but was challenged …

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Innodb Second Start prevention bug ?

I filed the following bug today. Basically it looks like in certain conditions Innodb may be started twice in the parallel on the same data files which can hurt database badly. It is true it …

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MySQL 4 to MySQL 5 Upgrade performance regressions

This week I already had two serious performance regression cases when upgrading from MySQL 4.0 and 4.1 to MySQL 5.0. By serious I mean several times performance difference not just 5-10% you often see for …

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MySQL Installation and upgrade scripts.

I generally find MySQL Sever sufficiently tested, meaning at least minor version upgrades rarely cause the problems. Of course it is not perfect and I remember number of big issues when some releases could not …

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MySQL Replication and Slow Queries

I just filed a bug regarding slow queries executed by replication thread are not being logged to the slow query log. This is not a big deal but it is ugly little gotcha which I …

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