November 24, 2014

Avoiding MySQL ALTER table downtime

MySQL table alterations can interrupt production traffic causing bad customer experience or in worst cases, loss of revenue. Not all DBAs, developers, syadmins know MySQL well enough to avoid this pitfall. DBAs usually encounter these kinds of production interruptions when working with upgrade scripts that touch both application and database or if an inexperienced admin/dev […]

Why ALTER TABLE runs faster on Percona Server 5.5 vs. MySQL 5.5

Some of us Perconians are at OpenStack summit this week in Atlanta. Matt Griffin, our director of product management, tweeted about the turbo-hipster CI talk about their experience of ALTER TABLEs running faster on Percona Server. Oracle’s Morgan Tocker then tweeted in response, asking why this was the case. I decided that the simplest way to […]

How to monitor ALTER TABLE progress in MySQL

While working on a recent support issue as a Percona Support Engineer,  I got one question from a customer asking how to monitor ALTER TABLE progress. Actually, for MySQL 5.5 and prior versions, it’s quite difficult to ALTER the table in a running production environment especially for large tables (with millions records). Because it will rebuild and lock the table […]

Why ALTER TABLE shows as two transactions in SHOW ENGINE INNODB STATUS

When executing an ALTER TABLE, InnoDB (and XtraDB) will create two InnoDB transactions: One transaction is created when the table being ALTERed is locked by the server. This will show up as something like “TABLE LOCK table schema.table_name trx id XXXX lock mode S” in SHOW ENGINE INNODB STATUS. Another is created when adding or […]

ALTER TABLE: Creating Index by Sort and Buffer Pool Size

Today I was looking at the ALTER TABLE performance with fast index creation and without it with different buffer pool sizes. Results are pretty interesting. I used modified Sysbench table for these tests because original table as initially created only has index on column K which initially contains only zeros, which means index is very […]

Should you name indexes while doing ALTER TABLE ?

MySQL Server does not require you to specify name of the index if you’re running ALTER TABLE statement – it is optional. Though what might be good practical reasons to specify the key name or omit ? Things what you should be looking at is how MySQL names indexes automatically as well as what maintaining […]

Hacking to make ALTER TABLE online for certain changes

Suppose you want to remove auto_increment from 100G table. No matter if it’s InnoDB or MyISAM, you’d usually ALTER TABLE huge_table CHANGE id id int(6) NOT NULL and then wait hours for table rebuild to complete. If you’re unlucky i.e. you have a lot of indexes and not too much RAM – you could end […]

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 […]

Recover orphaned InnoDB partition tablespaces in MySQL

A few months back, Michael wrote about reconnecting orphaned *.ibd files using MySQL 5.6. I will show you the same procedure, this time for partitioned tables. An InnoDB partition is also a self-contained tablespace in itself so you can use the same method described in the previous post. To begin with, I have an example […]

Syncing MySQL slave table with pt-online-schema-change

I recently encountered a situation in which after running Percona Toolkit’s pt-table-checksum on a customer system, 95% of the table on the MySQL master was different on the MySQL slave. Although this table was not a critical part of the infrastructure, from time to time, writes to the table from the master would break replication. […]