Emergency

Search Results for: mysql distinct on one column

How to avoid hash collisions when using MySQL’s CRC32 function

Percona Toolkit’s  pt-table-checksum performs an online replication consistency check by executing checksum queries on the master, which produces different results on replicas that are inconsistent with the master – and the tool pt-table-sync synchronizes data …

Read More
 

Parallel Query for MySQL with Shard-Query

While Shard-Query can work over multiple nodes, this blog post focuses on using Shard-Query with a single node.  Shard-Query can add parallelism to queries which use partitioned tables.  Very large tables can often be partitioned fairly …

Read More
 

Using Flexviews – part one, introduction to materialized views

If you know me, then you probably have heard of Flexviews. If not, then it might not be familiar to you. I’m giving a talk on it at the MySQL 2011 CE, and I figured …

Read More
 

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 …

Read More
 

The MySQL optimizer, the OS cache, and sequential versus random I/O

In my post on estimating query completion time, I wrote about how I measured the performance on a join between a few tables in a typical star schema data warehousing scenario. In short, a query …

Read More
 

Why MySQL could be slow with large tables ?

If you’ve been reading enough database related forums, mailing lists or blogs you probably heard complains about MySQL being unable to handle more than 1.000.000 (or select any other number) rows by some of the …

Read More
 

Followup questions to ‘What’s new in Percona XtraDB Cluster 5.6’ webinar

Thanks to all who attended my webinar yesterday.  The slides and recording are available on the webinar’s page.  I was a bit overwhelmed with the amount of questions that came in and I’ll try to …

Read More
 

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 …

Read More
 

Concatenating MyISAM files

Recently, I found myself involved in the migration of a large read-only InnoDB database to MyISAM (eventually packed). The only issue was that for one of the table, we were talking of 5 TB of …

Read More
 

Tools and Techniques for Index Design Webinar Questions Followup

I presented a webinar this week to give an overview of Tools and Techniques for Index Design. Even if you missed the webinar, you can register for it, and you’ll be emailed a link to …

Read More