One of our customers had a question related to the right value of Galera Cache size (gcache.size) in Galera Cluster for MySQL which I would like to share with you.

The question was: My maintenance window takes 4 hours for my 5TB DB. How can I avoid an SST ?!

Basically, having too small GCache size will lead to SST (Snapshot State Transfer) instead of IST (Incremental State Transfer), thus we can avoid the SST by setting the GCache to the appropriate value.

To check the current value of the GCache size:

mysql> SHOW GLOBAL VARIABLES LIKE 'wsrep_provider_options'\G
Variable_name: wsrep_provider_options
        Value: base_host = 192.168.1.12;
.
.
.
gcache.page_size = 128M; gcache.size = 128M; gcs.fc_debug = 0;
.
.
.

The value of GCache size could be changed by adding …

Finding bugs in MySQL is not only fun, it’s also something I have been doing the last four years of my life.

Whether you want to become the next Shane Bester (who is generally considered the most skilled MySQL bug hunter worldwide), or just want to prove you can outsmart some of the world’s best programmers, finding bugs in MySQL is a skill not reserved anymore to top QA engineers armed with a loads of scripts, expensive flash storage and top-range server hardware. Off course, for professionals that’s still the way to go, but now anyone with an average laptop and a standard HDD can have a lot of fun trying to find that elusive crash…

 If you follow this post carefully, you may well be able to find a nice crashing bug (or two) running RQG …

Consider the following commands, executed in the MySQL CLI on a new connection with no special preparation (and pay special attention to the execution time):

mysql> show create table t \G
*************************** 1. row ***************************
       Table: t
Create Table: CREATE TABLE `t` (
  `a` int(10) unsigned NOT NULL,
  `b` int(10) unsigned NOT NULL,
  PRIMARY KEY (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> select * from t;
Empty set (5.20 sec)

mysql> select count(*) from t;
+----------+
| count(*) |
+----------+
|        0 |
+----------+
1 row in set (5.22 sec)

mysql> select * from t where a = 10;
Empty set (0.00 sec)

mysql> select * from t where a < 10;
Empty set (5.35 sec)

mysql> select * from t where a > 10;
Empty set (5.41 sec)

mysql> select * from t where a in (10, 20, 30);
Empty set (0.00 sec)

mysql> select * from t where a > 1000000;
Empty set (0.00 sec)

mysql> select * …

InnoDB implements multi-version concurrency control (MVCC), meaning that different users will see different versions of the data they are interacting with (sometimes called snapshots, which is a bit of a misleading term). This is done in order to allow users to see a consistent view of the system without expensive and performance-constraining locking which would limit concurrency. (This is where the “concurrency control” part of the term comes from; one alternative is locking everything the user may need.) Undo logging and InnoDB’s “history” system are the mechanisms that underly its implementation of MVCC, but the way this works is generally very poorly understood.

InnoDB keeps a copy of everything that is changed

The key thing to …

The biggest concern with a slave is to ensure your data is consistent with the master! End of story!

3 of the biggest things I see when dealing with out-of-sync slaves:

1. Many users do not use the --read-only option on their slaves.
2. Some of those who do often have numerous users with SUPER who can still perform writes.
3. Many users simply use --slave-skip-errors=… to avoid common errors.

Of course, if you have a slave, definitely use the --read-only option.

However, SUPER users can still write on slaves with --read-only, so blindly granting SUPER to all users just to save a little time when creating users won’t help. I’d suggest to use SUPER as sparingly as possible (not to mention it’s good for security also).

And the use of --slave-skip-errors=… is generally just a quick fix to avoid errors on the slave, but a sure fire way to end up with inconsistent …

210 people registered for the inaugural “Open Source Appreciation Day” March 31 in Santa Clara, Calif. The event will be held each year at Percona Live henceforth.

To kick off the Percona Live MySQL Conference & Expo 2014, Percona held the first “Open Source Appreciation Day” on Monday, March 31st. Over 210 people registered and the day’s two free events focused on CentOS and OpenStack.

The OpenStack Today event brought together members of the …

MySQL 5.7.4 was recently released (it is the latest MySQL 5.7, and is the “m14″ or “Milestone 14″ release), and is available for download here and here.

The 5.7.4 changelog begins with the following, so I felt it appropriate to include it here as well.

In Memoriam:

“This release is dedicated to the memory of two young engineers of the MySQL Engineering family, Astha and Akhila, whom we lost while they were in their early twenties. This is a small remembrance and a way to recognize your contribution to the 5.7 release. You will be missed.”

http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-4.html

As for the fixes, there are …

As I’ve mentioned in previous posts, TokuMX replication differs quite a bit from MongoDB’s replication. The differences are large enough such that we’ve completely redone some of MongoDB’s existing algorithms. One such area is how secondaries apply oplog data from a primary. In this post, I’ll explain how.

In designing how secondaries apply oplog data, we did not look closely at how MongoDB does it. In fact, I’ve currently forgotten all I’ve learned about MongoDB’s implementation, so I am not in a position to compare the two. I think I recall that MongoDB’s oplog idempotency was a key to their algorithms. Because we chose …

I recently helped a client implement a custom replication delay monitor and wanted to share the experience and discuss some of the iterations and decisions that were made. percona-millipede was developed in conjunction with Vimeo with the following high-level goal in mind: implement a millisecond level replication delay monitor and graph the results.  Please visit http://making.vimeo.com for more information and thanks to Vimeo for sharing this tool!

Here is the rough list of iterations we worked through in developing this tool/process:

1. Standard pt-heartbeat update/monitor
2. Asynchronous, threaded update/monitor tool
3. Synchronized (via zeroMQ), threaded version of the tool

pt-heartbeat

Initially, we had been running …

Installing Apache2 With PHP5 And MySQL Support On Fedora 20 (LAMP)

LAMP is short for Linux, Apache, MySQL, PHP. This tutorial shows how you can install an Apache2 webserver on a Fedora 20 server with PHP5 support (mod_php) and MySQL support.