Join 7000 others and follow Sean Hull on twitter @hullsean. MySQL’s optimizer can do a lot of things, but subqueries are not always handled well. Take a look at the IN subquery below. If you see the DEPENDENT SUBQUERY in your explain plan, you may want to take a second look. This will run slow [...]

Join 6100 others and follow Sean Hull on twitter @hullsean. There are two ways to speedup UNIONs in a MySQL database. First use UNION ALL if at all possible, and second try to push down your conditions. [mytweetlinks] 1. UNION ALL is much faster than UNION How does a UNION work? Imagine you have two [...]

Join 6100 others and follow Sean Hull on twitter @hullsean. The Foundation of Speed All servers use disk to store files. Operating system libraries, webserver & application code, and most importantly databases all use disk constantly. So disk speed is crucial to server speed. [mytweetlinks] [quote] Disk speed is crucial for MySQL databases. It has [...]

Read the original article at Five More Things Deadly to Scalability

Join 6000 others and follow Sean Hull on twitter @hullsean. 1. Slow Disk I/O – RAID 5 – Multi-tenant EBS Disk is the grounding of all your servers, and the base of their performance. True with larger and larger main memory, much is available in cache, a server still needs to constantly read from disk [...]

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We’ve told you all about MySQL mult-master replication’s limitations. If you write to two masters it is bound to fail for myriad reasons. Now what? Do what the pros do that’s what. A. Don’t write to both masters Using multi-master replication works great as long as you do so in active-passive mode. Never write to [...]

April 26, 2013 By Severalnines

This post shows you how to move from a single instance Drupal/MySQL to a multi-server environment. A well designed multi-server deployment not only allows Drupal to scale, but will also enhance redundancy by removing single points of failure. Components used are Apache, PHP, csync2, lsyncd, Keepalived, HAproxy, MySQL Galera Cluster and ClusterControl.

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Here’s the last nail in the coffin. We hope this convinces you not to write to multiple masters with MySQL replication. Reason 10 – No tools to reconcile inconsistent masters For all the endless reasons we’ve already outlined MySQL replication is prone to failure. We know it’s going to happen, you now know too. When [...]

If you’re not convinced yet that writing to dual masters is a bad idea, we have a couple more reasons. 9. Temp tables break replication after restart MySQL’s replication is sensitive to temporary tables. You shouldn’t use them. If your queries create them to work against, and a node crashes, the temp tables will be [...]

Read the original article at Crashed nodes corrupt your MySQL cluster

Writing to two masters is like walking around with a loaded shotgun. Eventually one of your instances will fail and when it does, replications position & synchronization information could easily become corrupt! Reason 8 – Crashed nodes cause big problems MySQL instances, unfortunately can crash. When that happens, they don’t always sync the replication position [...]

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Read the original article at Transaction isolation breaks when writing two masters

Continuing our discussion of multi-master replication, we hit on five more reasons why writing to two masters aka active-active replication is very dangerous. Click through to the end for multi-master solutions that work with MySQL. Reason 6 – You lose transaction isolation This may sound like a theoretical point to some. But hopefully we can [...]

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