September 16, 2014

Using MMM to ALTER huge tables

Few months ago, I wrote about a faster way to do certain table modifications online. It works well when all you want is to remove auto_increment or change ENUM values. When it comes to changes that really require table to be rebuilt – adding/dropping columns or indexes, changing data type, converting data to different character […]

Using VIEW to reduce number of tables used

Many Open Source software solutions use database per user (or set of tables per user) which starts to cause problems if it is used on massive scale (blog hosting, forum hosting etc), resulting of hundreds of thousands if not millions of tables per server which can become really inefficient. It is especially inefficient with Innodb […]

What exactly is read_rnd_buffer_size

Looking for documentation for read_rnd_buffer_size you would find descriptions such as “The read_rnd_buffer_size is used after a sort, when reading rows in sorted order. If you use many queries with ORDER BY, upping this can improve performance” which is cool but it does not really tell you how exactly read_rnd_buffer_size works as well as which […]

Using CHAR keys for joins, how much is the overhead ?

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 to benchmark. The results below are for […]

TMP_TABLE_SIZE and MAX_HEAP_TABLE_SIZE

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 it you should increase tmp_table_size to appropriate value and avoid using blob/text columns which force table creation on the disk because MEMORY storage engine does not support them Right ? […]

Covering index and prefix indexes

I already wrote in the blog as well mentioned in presentation there is often a choice you have to make between having prefix index – which can be significantly smaller in size and having index being covering index, which means query can be executed using only data from the index without reading the row itself. […]

Why Index could refuse to work ?

Have you ever seen index which refused to be used even if there is every reason for it to work (from the glance view):

Why on the earth index would not be used you would think, even if MySQL is mentioning it in “possible keys” ? Should you try to force it ?

INSERT ON DUPLICATE KEY UPDATE and summary counters.

INSERT … ON DUPLICATE KEY UPDATE is very powerful but often forgotten MySQL feature. It was introduced in MySQL 4.1 but I still constantly see people unaware of it. Myself I like this feature big deal because it is designed in truly MySQL style – very efficient solution for freqent task while keeping it beautiful […]