The parameter sort_buffer_size is one the MySQL parameters that is far from obvious to adjust. It is a per session buffer that is allocated every time it is needed. The problem with the sort buffer comes from the way Linux allocates memory. Monty Taylor (here) have described the underlying issue in detail, but basically above [...]
Sharing an auto_increment value across multiple MySQL tables
October 4, 2010 By 9 Comments
The title is SEO bait – you can’t do it. We’ve seen a few recurring patterns trying to achieve similar – and I thought I would share with you my favorite two: Option #1: Use a table to insert into, and grab the insert_id:
1 2 3 4 5 | CREATE TABLE option1 (id int not null primary key auto_increment) engine=innodb; # each insert does one operations to get the value: INSERT INTO option1 VALUES (NULL); # $connection->insert_id(); |
Option #2: Use a table with one just row:
1 2 3 4 5 6 | CREATE TABLE option2 (id int not null primary key) engine=innodb; INSERT INTO option2 VALUES (1); # start from 1 # each insert does two operations to get the value: UPDATE option2 SET id=@id:=id+1; SELECT @id; |
UDF -vs- MySQL Stored Function
September 6, 2010 By 8 Comments
Few days ago I was working on a case where we needed to modify a lot of data before pushing it to sphinx – MySQL did not have a function to do the thing so I thought I’ll write MySQL Stored Function and we’ll be good to go. It worked! But not so well really [...]
How fast is FLUSH TABLES WITH READ LOCK?
April 24, 2010 By 30 Comments
A week or so ago at the MySQL conference, I visited one of the backup vendors in the Expo Hall. I started to chat with them about their MySQL backup product. One of the representatives told me that their backup product uses FLUSH TABLES WITH READ LOCK, which he admitted takes a global lock on [...]
When should you store serialized objects in the database?
January 21, 2010 By 47 Comments
A while back Friendfeed posted a blog post explaining how they changed from storing data in MySQL columns to serializing data and just storing it inside TEXT/BLOB columns. It seems that since then, the technique has gotten more popular with Ruby gems now around to do this for you automatically.
Upgrading MySQL
January 5, 2010 By 23 Comments
Upgrading MySQL Server is a very interesting task as you can approach it with so much different “depth”. For some this is 15 minutes job for others it is many month projects. Why is that ? Performing MySQL upgrade two things should normally worry you. It is Regressions – functionality regressions when what you’ve been [...]
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 [...]
Air traffic queries in LucidDB
October 26, 2009 By 20 Comments
After my first post Analyzing air traffic performance with InfoBright and MonetDB where I was not able to finish task with LucidDB, John Sichi contacted me with help to setup. You can see instruction how to load data on LucidDB Wiki page You can find the description of benchmark in original post, there I will [...]
3 ways MySQL uses indexes
September 12, 2009 By 28 Comments
I often see people confuse different ways MySQL can use indexing, getting wrong ideas on what query performance they should expect. There are 3 main ways how MySQL can use the indexes for query execution, which are not mutually exclusive, in fact some queries will use indexes for all 3 purposes listed here.
Just do the math!
July 6, 2009 By 4 Comments
One of the most typical reasons for performance and scalability problems I encounter is simply failing to do the math. And these are typically bad one because it often leads to implementing architectures which are not up for job they are intended to solve. Let me start with example to make it clear. Lets say [...]
