July 23, 2014

Improved InnoDB fast index creation

One of the serious limitations in the fast index creation feature introduced in the InnoDB plugin is that it only works when indexes are explicitly created using ALTER TABLE or CREATE INDEX. Peter has already blogged about it before, here I’ll just briefly reiterate other cases that might benefit from that feature: when ALTER TABLE […]

Why you should ignore MySQL’s key cache hit ratio

I have not caused a fist fight in a while, so it’s time to take off the gloves. I claim that somewhere around of 99% of advice about tuning MySQL’s key cache hit ratio is wrong, even when you hear it from experts. There are two major problems with the key buffer hit ratio, and […]

Multi Column indexes vs Index Merge

The mistake I commonly see among MySQL users is how indexes are created. Quite commonly people just index individual columns as they are referenced in where clause thinking this is the optimal indexing strategy. For example if I would have something like AGE=18 AND STATE=’CA’ they would create 2 separate indexes on AGE and STATE […]

check-unused-keys: A tool to interact with INDEX_STATISTICS

With the growing adoption of Google’s User Statistics Patch**, the need for supporting scripts has become clear. To that end, we’ve created check-unused-keys, a Perl script to provide a nicer interface than directly querying the INFORMATION_SCHEMA database.

A rule of thumb for choosing column order in indexes

I wanted to share a little rule of thumb I sometimes use to decide which columns should come first in an index. This is not specific to MySQL, it’s generally applicable to any database server with b-tree indexes. And there are a bunch of subtleties, but I will also ignore those for the sake of […]

Do you always need index on WHERE column ?

I believe we wrote about this before, but this topic popups again and again. Today I’ve read opinion that if we have clause WHERE has_something=1 we should have index on column has_something (the column has two values 0 and 1). In reality the right answer is not so simple.

Indexes in MySQL

MySQL does not always make a right decision about indexes usage. Condsider a simple table:

; 250001 (V1)

; 83036 (V2) (execution time = 110 ms) That is index selectivity by condition (ID1=1) is V2/V1 = 0.3321 or 33.21% It is said (e.g. book “SQL Tuning”) if selectivity over 20% then a full table […]

Row-based replication, MySQL 5.6 upgrades and temporal data types

Whither your rollback plan? MySQL 5.6 upgrades are in full swing these days and knowing how to safely upgrade from MySQL 5.5 to 5.6 is important. When upgrading a replication environment, it’s important that you can build a migration plan that safely allows for your upgrade with minimal risk — rollback is often a very […]

How to identify and cure MySQL replication slave lag

Here on the Percona MySQL Support team, we often see issues where a customer is complaining about replication delays – and many times the problem ends up being tied to MySQL replication slave lag. This of course is nothing new for MySQL users and we’ve had a few posts here on the MySQL Performance Blog […]

Percona XtraDB Cluster 5.6.15-25.5 is now available

Percona is glad to announce the new release of Percona XtraDB Cluster 5.6 on March 20th 2014. Binaries are available from downloads area or from our software repositories. Based on Percona Server 5.6.15-63.0 including all the bug fixes in it, Galera Replicator 3.4 and on Codership wsrep API 25.5 is now the current General Availability […]