Overview The Skinny

In this blog post we explore various options for tuning MySQL traffic routing in the Tungsten Connector for better control of the distribution.

A Tungsten Cluster relies upon the Tungsten Connector to route client requests to the master node or optionally to the slaves. The Connector makes decisions about where to route requests based on a number of factors.

This blog post will focus on the Load Balancer algorithms available via configuration that allow you to adjust the routing behavior of the Connector, along with ways to debug the Connector Load Balancer’s routing decisions.

The Question Recently, a customer asked us:

How do I know which load balancer algorithm is in use by the Connector? And how do we enable debug logging for the Connector load balancer?

Not a big deal, but I just added a “Table of Contents” page to my blog to make finding older articles much easier.

I noticed most of my posts are quite lengthy, and it can take a bit of searching/clicking to find an older entry. So unless you happen to recall the ‘month/year’ it was published, which I don’t even remember that, then hopefully this will help.

Really simple, and looks just like this:

• Microseconds and MariaDB
• Dealing with Assertion failure in log/log0recv.c – !page || (ibool)!!page_is_comp(page) == dict_table_is_comp(index->table)
• MySQL Windows Users – Use Grep to Search MySQL Source Code
• …

Before I start a story about the data recovery case I worked on yesterday, here's a quick tip - having a database backup does not mean you can restore from it. Always verify your backup can be used to restore the database! If not automatically, do this manually, at least once a month. No, seriously - in most of the recovery cases I worked on, customers did have some sort of backup, but it just wasn't working, complete and what not. Someone set it up and never bothered to check if it still works after a while.

Anyway, this post is not really about the backups but rather about few interesting things I learned during last recovery case.

First, some facts about the system and how data was lost:

• MySQL had a dedicated partition on XFS file system
• Server was running innodb_file_per_table
• There was a …

A broken VIEW was caused by the view’s definer being non-existent. In this particular system, backups are done by replicating all the machines (production, development, test, etc) to one server and doing cold physical backups off that server, which currently has 12 instances running.

So in order to find on what machine the user might still be defined, I went to the backup server. All the data directories are in one path, ie:

instance 1 has a datadir of /data/mysql/instance1
instance 2 has a datadir of /data/mysql/instance2

Now, the unix tool strings can be used against many types of files. In particular, though, you can use strings on the mysql/user.MYD file to see the username, host, and password hash. (note that strings only shows strings longer than 3 characters, so if your host or username is 3 characters or less, it will not show up in the output of strings. You …

I’m decently familiar with grep so I can usually make it do what I want. I frequently need to search for instance MySQL source code for certain pattern strings, and this makes life so much easier. But Akash pointed out ack to me, which has the specific tagline “better than grep” (has the domain even) and I reckon it does live up to that. Win! It’s written in pure Perl, very easy to install (doesn’t even use CPAN if you don’t want).

It recurses into subdirs by default, while ignoring stuff like revision control and binary files. You can search specific types of files through a symbolic name rather than by specifying regexes. And it has colour highlighting, and simply uses the familiar Perl regexes for its pattern matching rather than funky subsets of which there are many distinct ones…