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MySQL Quality of old and new features

 | October 4, 2007 |  Posted In: Insight for DBAs

Recent couple of days our team was pointed to number of bugs in MySQL 5.0 which again seriously shakes the confidence in both MySQL Quality Control and bug fix promptness. Let me just take couple of bugs as examples: Triggers broken with auto-increment columns for Innodb tables (bug 26316). As you can see this bug […]

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Read Buffers, mmap, malloc and MySQL Performance

 | September 12, 2007 |  Posted In: Insight for DBAs

Monty Taylor posted interesting investigation of the fact read_buffer_size variable affects connection speed. This is not something you would expect right ? me too. Not only global user data is expected to be cached on startup but even if it is not why would you do full table scan to fetch single user information ? […]

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MySQL VIEW as performance troublemaker

 | August 12, 2007 |  Posted In: Insight for DBAs

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 how it affects server performance. Even worse than that – looking at the short table which just gets single row […]

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Query_cache and column level privileges

 | August 6, 2007 |  Posted In: Insight for Developers

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 the query_cache is not able to know which columns are accessed. Looking into source code I found out that in […]

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More Gotchas with MySQL 5.0

 | July 27, 2007 |  Posted In: Insight for DBAs

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 close look revealed this is the function which is used to compute number of latched pages in Innodb Buffer Pool, […]

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MySQL 5.0 Community Edition Regression

 | July 27, 2007 |  Posted In: Insight for DBAs

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 with SHOW PROFILE patch available in latest MySQL Community Edition and I’ve been troubleshooting customer affected by one of […]

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Innodb Second Start prevention bug ?

 | June 16, 2007 |  Posted In: Insight for DBAs

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 does not seems to be 100% repeatable but I’ve seen it multiple times in different environments. I’m not sure if […]

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MySQL 4 to MySQL 5 Upgrade performance regressions

 | June 6, 2007 |  Posted In: Insight for DBAs

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 simple queries due to generally fatter code. The problem in both cases was MySQL 5.0 broken group commit bug. First […]

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