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Search Results for: explain using index

Find unused indexes

I wrote one week ago about how to find duplicate indexes. This time we’ll learn how to find unused indexes to continue improving our schema and the overall performance. There are different possibilites and we’ll …


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 …


When EXPLAIN estimates can go wrong!

I have been working with a few customer cases and one interesting case popped up. The customer was facing a peculiar problem where the rows column in the EXPLAIN output of the query was totally …


Understanding Indexing – NY Effective MySQL Meetup

At next week’s NY Effective MySQL Meetup, I will give a talk: “Understanding Indexing: Three rules on making indexes around queries to provide good performance.” The meetup is 7 pm Tuesday, October 11th, and will …


Explaining Indexes with a Library Metaphor

My favorite metaphor for explaining indexes is comparing them to index cards in an old library. In an old library, you used to (or still do) have index cards at the front desk which have …


Understanding Indexing – SF MySQL Meetup

At this week’s SF MySQL Meetup, I will give a talk: “Understanding Indexing: Three rules on making indexes around queries to provide good performance.” The meetup is 7 pm tomorrow (Wednesday, 6/22), and will be …


Understanding Indexing – MySQL Meetup

Yesterday, at the Boston MySQL Meetup, I gave a talk on indexing. It is posted here (also goo.gl/S2LBe). In short, indexes are used to improve query performance. As a result, good indexes are designed around …


Advanced index analysis with mk-index-usage

The new release of Maatkit has a useful feature in mk-index-usage to help you determine how indexes are used in more flexible ways. The default report just prints out ALTER statements for removing unused indexes, …


EXPLAIN EXTENDED can tell you all kinds of interesting things

While many people are familiar with the MySQL EXPLAIN command, fewer people are familiar with “extended explain” which was added in MySQL 4.1 EXPLAIN EXTENDED can show you what the MySQL optimizer does to your …


Extending Index for Innodb tables can hurt performance in a surprising way

One schema optimization we often do is extending index when there are queries which can use more key part. Typically this is safe operation, unless index length increases dramatically queries which can use index can …