Until MySQL 5.5 the only variable used to identify a network connectivity problem between Master and Slave was slave-net-timeout. This variable specifies the number of seconds to wait for more Binary Logs events from the master before abort the connection and establish it again. With a default value of 3600 this has been a historically [...]
Joining on range? Wrong!
May 17, 2010 By 10 Comments
The problem I am going to describe is likely to be around since the very beginning of MySQL, however unless you carefully analyse and profile your queries, it might easily go unnoticed. I used it as one of the examples in our talk given at phpDay.it conference last week to demonstrate some pitfalls one may [...]
InnoDB: look after fragmentation
November 5, 2009 By 12 Comments
One problem made me puzzled for couple hours, but it was really interesting to figure out what’s going on. So let me introduce problem at first. The table is
1 2 3 4 5 6 7 8 | CREATE TABLE `c` ( `tracker_id` int(10) unsigned NOT NULL, `username` char(20) character set latin1 collate latin1_bin NOT NULL, `time_id` date NOT NULL, `block_id` int(10) unsigned default NULL, PRIMARY KEY (`tracker_id`,`username`,`time_id`), KEY `block_id` (`block_id`) ) ENGINE=InnoDB |
Table has 11864696 rows and takes Data_length: 698,351,616 bytes on disk The problem is that after restoring table from mysqldump, the query that scans data [...]
How Percona does a MySQL Performance Audit
November 24, 2008 By 17 Comments
Our customers or prospective customers often ask us how we do a performance audit (it’s our most popular service). I thought I should write a blog post that will both answer their question, so I can just reply “read all about it at this URL” and share our methodology with readers a little bit. This [...]
ANALYZE: MyISAM vs Innodb
September 3, 2008 By 9 Comments
Following up on my Previous Post I decided to do little test to see how accurate stats we can get for for Index Stats created by ANALYZE TABLE for MyISAM and Innodb. But before we go into that I wanted to highlight about using ANALYZE TABLE in production as some people seems to be thinking [...]
Can MySQL temporary tables be made safe for statement-based replication?
May 26, 2008 By 8 Comments
A while ago I wrote about how to make MySQL replication reliable, part of which is to eliminate temporary tables. The idea is this: if a slave is stopped (or crashed) while a temporary table is open and is then restarted, the temporary table doesn’t exist anymore, and the slave will have problems trying to [...]
How fast can you sort data with MySQL ?
August 18, 2007 By 26 Comments
I took the same table as I used for MySQL Group by Performance Tests to see how much MySQL can sort 1.000.000 rows, or rather return top 10 rows from sorted result set which is the most typical way sorting is used in practice. I tested full table scan of the table completes in 0.22 [...]
How much overhead is caused by on disk temporary tables
August 16, 2007 By 26 Comments
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 disk as MYISAM tables. Which one will be used depends on the allowed tmp_table_size and also by the data which [...]
Query_cache and column level privileges
August 6, 2007 By 5 Comments
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 [...]
Test Drive of Solid
September 22, 2006 By 5 Comments
Not so long ago Solid released solidDB for MySQL Beta 3 so I decided now is time to take a bit closer look on new transactional engine for MySQL. While my far goal is the performance and scalability testing before I wanted to look at basic transactional properties such as deadlock detection, select for update [...]
