by Peter Zaitsev | Jul 27, 2007 | 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...
by Peter Zaitsev | Jul 27, 2007 | 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...
by Peter Zaitsev | Jun 18, 2007 | Insight for Developers
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 with rightful question about the difference. I did not know so I decided...
by Peter Zaitsev | Jun 16, 2007 | 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...
by Peter Zaitsev | Jun 6, 2007 | 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...
by Peter Zaitsev | May 21, 2007 | Insight for DBAs
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 be used due to behavior changes in them and when something...
by Peter Zaitsev | Mar 28, 2007 | Insight for DBAs
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 think few people know about. It is especially bad if you’re using tools to analyze...
by Andrew Aksyonoff | Mar 27, 2007 | Insight for Developers
by Peter Zaitsev | Feb 14, 2007 | Insight for DBAs
I was working with customer today which has MySQL on a system with some 64GB or RAM running MyISAM, so they set key_buffer_size to 16G… and every few days MySQL crashes. Why ? Because key_buffer_size over 4GB in size is not really supported (checked with latest...
by Peter Zaitsev | Jan 31, 2007 | Insight for DBAs
There is one bug, or “missing feature” in MySQL Optimizer which may give you hard time causing performance problems which may be hard to track down, it is using only part of the index when full index can be used or using shorter index while there is longer...
by Peter Zaitsev | Jan 19, 2007 | Insight for DBAs
We all know disk based temporary tables are bad and you should try to have implicit temporary tables created in memory where possible, do to the fact that you should increase tmp_table_size to appropriate value and avoid using blob/text columns which force table...
by Vadim Tkachenko | Jan 3, 2007 | Benchmarks
There was several changes in InnoDB to fix scalabilty problems, so I ran benchmark to check new results and also compare overall performance of InnoDB in 5.0 and 5.1 before and after fixes. Problems in InnoDB that were fixed: Thread trashing issues with count of...
by Peter Zaitsev | Nov 30, 2006 | Benchmarks
I had found pile of MySQL and PostgreSQL benchmarks on various platforms which I have not seen before. Very interesting reading. It does not share too much information about how MySQL or PostgreSQL was configured or about queries. Furthermore MySQL and PostgreSQL has...
by Peter Zaitsev | Nov 21, 2006 | Insight for DBAs
I was restarting MySQL on box with 50.000 of Innodb tables and again it took couple of hours to reach decent performance because of “Opening Tables” stage was taking long. Part of the problem is Innodb is updating stats on each table open which is possibly...
by Vadim Tkachenko | Nov 14, 2006 | Insight for DBAs
I was pretty busy last month with project which will be annonced very soon (I hope), but I can’t miss bug fix of my favorite bug 15815. I wrote about this problem before and also investigated in my presentation. Finally bug fix was pushed into 5.0-bk tree and...
by Peter Zaitsev | Oct 3, 2006 | Insight for DBAs
Innodb primary key is special in many senses and I was always wondering how well MySQL is integrated with Innodb to take advantage of these special features. Lets see which things work and which things do not: I used the following simple table for tests: CREATE TABLE...
by Vadim Tkachenko | Sep 22, 2006 | Uncategorized
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...
by Peter Zaitsev | Sep 4, 2006 | Insight for DBAs
I already wrote couple of weeks ago I keep most of my systems on MySQL 4.1 still as they will not benefit from MySQL 5.0 features anyway while I do not want to likely loose a bit of performance and possibly deal with new bugs and changes introduced in MySQL 5.0 (You...
by Vadim Tkachenko | Jul 28, 2006 | Insight for DBAs
I’m again returning to InnoDB scalability and related bug #15815 as it hurts many users and customers using multi-cpu servers. Short intro into problem: On 4-CPU box 1 thread executes full-table scan select query for 8 sec, but with 4 threads – each thread...
by Vadim Tkachenko | Jun 5, 2006 | Insight for DBAs
InnoDB has a mechanism to regulate count of threads working inside InnoDB. innodb_thread_concurrency is variable which set this count, and there are two friendly variables innodb_thread_sleep_delay and innodb_concurrency_tickets. I’ll try to explain how it...
