November 24, 2014

MySQL-Memcached or NOSQL Tokyo Tyrant – part 1

All to often people force themselves into using a database like MySQL with no thought into whether if its the best solution to there problem. Why?  Because their other applications use it, so why not the new application?  Over the past couple of months I have been doing a ton of work for clients who […]

MySQL random freezes could be the query cache

I feel like I’ve been seeing this a lot lately. occasionally, seemingly innocuous selects take unacceptably long. Or Over the past few weeks, we’ve been having bizarre outages during which everything seems to grind to a halt… and then fixes itself within 5 minutes. We’ve got plenty of memory, we’re not running into swap, and […]

The MySQL optimizer, the OS cache, and sequential versus random I/O

In my post on estimating query completion time, I wrote about how I measured the performance on a join between a few tables in a typical star schema data warehousing scenario. In short, a query that could take several days to run with one join order takes an hour with another, and the optimizer chose […]

MySQL Query Cache WhiteSpace and comments

Commenting on my previous post on MySQL Query Cache Gerry pokes me as I’m all wrong and both comments and whitespace are fixed in MySQL 5.0. This was not what I remember seeing in production so I decided to do some tests on the matter:

How MySQL Query Cache works with Transactions

As MySQL Manual Says Query Cache works with transactions with Innodb tables but it does not tell you how and with which restrictions. According to my tests it works but it is very restricted and one could expect it to work much better: The result set can be retrieved from query cache (for statements both […]

Query Profiling with MySQL: Bypassing caches

Quite frequently I run into question like this “I’m using SQL_NO_CACHE but my query is still much faster second time I run it, why is that ? The answer to this question is simple – because SQL_NO_CACHE only bypasses query cache but it has no change on other caches, which are MySQL Caches – Innodb […]

MySQL Query Cache and prepared statements – support comming ?

Looking at post by Konstantin Osipov we should finally get Query Cache working with prepared statements in MySQL 5.1 The interesting thing Konstantin notes it just took few days to fix it – I believe MySQL Support Team alone spent much more times explaining customers why is it not done or troubleshooting cases with wrong […]

MySQL Query Cache

MySQL has a great feature called “Query Cache” which is quite helpful for MySQL Performance optimization tasks but there are number of things you need to know. First let me clarify what MySQL Query Cache is – I’ve seen number of people being confused, thinking MySQL Query Cache is the same as Oracle Query Cache […]

What MySQL buffer cache hit rate should you target

“What cache hit rate is good for optimal MySQL Performance” is typical question I’m asked. It could by MyISAM key_buffer or Innodb innodb_buffer_pool it does not really matter. In both cases trying to come up with constant “good” hit rate is looking for trouble. Well of course you can name 100% hit rate and all […]

Sys Schema for MySQL 5.6 and MySQL 5.7

Performance Schema (P_S) has been available since MySQL 5.5, more than 4 years ago. It is still difficult to see production servers with P_S enabled, even with MySQL 5.6 where the feature is enabled by default. There have been several complaints like the overhead, that the fix is a work in progress, and the ease […]