October 21, 2014

Multiple column index vs multiple indexes with MySQL 5.6

A question often comes when talking about indexing: should we use multiple column indexes or multiple indexes on single columns? Peter Zaitsev wrote about it back in 2008 and the conclusion then was that a multiple column index is most often the best solution. But with all the recent optimizer improvements, is there anything different with […]

Multiple column index vs multiple indexes

(There is an updated version of the content in this post by Percona’s Stephane Combaudon available here.) After my previous post there were questions raised about Index Merge on Multiple Indexes vs Two Column Index efficiency. I mentioned in most cases when query can use both of the ways using multiple column index would be […]

Quickly finding unused indexes (and estimating their size)

I had a customer recently who needed to reduce their database size on disk quickly without a lot of messy schema redesign and application recoding.  They didn’t want to drop any actual data, and their index usage was fairly high, so we decided to look for unused indexes that could be removed. Collecting data It’s […]

Find and remove duplicate indexes

Having duplicate keys in our schemas can hurt the performance of our database: They make the optimizer phase slower because MySQL needs to examine more query plans. The storage engine needs to maintain, calculate and update more index statistics DML and even read queries can be slower because MySQL needs update fetch more data to […]

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 […]

3 ways MySQL uses indexes

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.

Using Multiple Key Caches for MyISAM Scalability

I have written before – MyISAM Does Not Scale, or it does quite well – two main things stopping you is table locks and global mutex on the KeyCache. Table Locks are not the issue for Read Only workload and write intensive workloads can be dealt with by using with many tables but Key Cache […]

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 […]

Duplicate indexes and redundant indexes

About every second application I look at has some tables which have redundant or duplicate indexes so its the time to speak about these a bit. So what is duplicate index ? This is when table has multiple indexes defined on the same columns. Sometimes it is indexes with different names, sometimes it is different […]

Percona Cloud Tools: Making MySQL performance easy

One of our primary focuses at Percona is performance. Let me make some statements on what is “performance.” In doing so I will refer to two pieces of content: Carry Millsap’s talk “Performance Instrumentation: Beyond What You Do Now” [1] White Paper (by Peter and Baron) “Goal-Driven Performance Optimization” [2] I highly recommend that you […]