… mentioned mysql slave queries are not logged to slow query log and it looks like I was wrong connecting it just with replication. In reality it is… so slow query logging had to be disabled for such queries. What does it mean ? Simply what you can’t really trust standard slow query log – some queries…
Post: What's required to tune MySQL?
July 27, 2011 By 4 Comments
… should expect to deliver huge wins. If MySQL is actually badly configured, you can hurt its performance…. Examples include what happens when you have query cache contention, DNS problems, or very slow I/O. … and let you know if something obscure is wrong with the configuration, it’s not likely to …
Post: How to Identify Bad Queries in MySQL
January 10, 2011 By 16 Comments
…wrong.) Here is my definition: Queries are bad either singly (an individual query is bad) or in aggregate (a group or class of queries is…MySQL for years. This is necessary for determining whether a group of queries completed in a cluster. One-second granularity (what…
Post: Is your server's performance about to degrade?
May 18, 2010 By 13 Comments
…with mk-query-digest. Side note: bravo for Daniel figuring out how to make mk-query-digest parse 2GB of slow query log with…what‘s going on. It’s possible that nothing can be done about it — and that’s where improvements to the MySQL…
Post: Reasons for MySQL Replication Lag
July 29, 2011 By 6 Comments
…MySQL Restart MySQL Restarts may include recovery time but what is the most important they often come with…is nice to analyze your replication traffic regularly with mk-query-digest (Percona Server marks Slave Thread in slow query log so it is… when backup taken at the wrong time may be responsible …
Post: Troubleshooting MySQL Upgrade Performance Regressions
February 15, 2012 By Leave a Comment
… and what thought to be slow down with version upgrade is rather …with MySQL Sandbox) can especially be helpful. Once you have spotted the query which performs differently between MySQL Server versions you should: Check Query…wrong plan from optimizer standpoint and updating stats may cause old MySQL…
Post: How Percona does a MySQL Performance Audit
November 24, 2008 By 17 Comments
…is happening 6 times every ten seconds. We need to figure out what is happening because it can indicate something else is wrong. This is…is very customer-specific, and we work with what we have. Sending the report to the client After the slow query log analysis is…
Post: Why you should ignore MySQL's key cache hit ratio
February 28, 2010 By 27 Comments
…MySQL‘s key cache hit ratio is wrong, even when you hear it from experts. There are two major problems with…have a query I know is slow and is a problem for my application. I have profiled it with SHOW…over it? What about InnoDB tuning? You might be wondering, what about InnoDB tuning? What is the …
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
…What is often forgotten about is – depending if workload is cached or not different selectivity might show benefit from using indexes. In fact even MySQL…
Post: A common problem when optimizing COUNT()
September 20, 2008 By 18 Comments
…do with a slow query is figure out what it’s trying to do. You can’t fully optimize a query … what they were trying to do with COUNT(). This is database-agnostic, not related to MySQL. The problem is …is not a good place to learn about what it does. 90% of what you can find online is just wrong…
