For processing SELECT queries MySQL needs some times the help of temporary tables. These temporary tables can be created either in memory or on disk.

The number of creations of such temporary tables can be found with the following command:

mysql> SHOW GLOBAL STATUS LIKE 'created_tmp%tables';
+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 4     |
| Created_tmp_tables      | 36    |
+-------------------------+-------+ …

After properly installing and testing a Galera Cluster we see that the set-up is not finished yet. It needs something in front of the Galera Cluster that balances the load over all nodes.
So we install a load balancer in front of the Galera Cluster. Typically nowadays HAProxy is chosen for this purpose. But then we find, that the whole Galera Cluster is still not high available in case the load balancer fails or dies. So we need a second load balancer for high availability.
But how should we properly …

We have recently seen a case where the following command was executed on a Galera Cluster node:

SQL> GRANT SUPER ON userdb.* TO root@127.0.0.111;
ERROR 1221 (HY000): Incorrect usage of DB GRANT and GLOBAL PRIVILEGES

2014-12-09 14:53:55 7457 [Warning] Did not write failed 'GRANT SUPER ON userdb.* TO root@127.0.0.111' into binary log while granting/revoking privileges in databases.
2014-12-09 14:53:55 7457 [ERROR] Slave SQL: Error 'Incorrect usage of DB GRANT and GLOBAL PRIVILEGES' on query. Default …

Precaution: Before you try this out on your production system do a BACKUP first! FromDual Backup Manager can help you with this.

Situation

A MySQL user has delete its InnoDB table files for example like this:

shell> rm -f $datadir/test/test.*

Analysis

We do some analysis first:

mysql> DROP TABLE test;
ERROR 1051 (42S02): Unknown table 'test'

mysql> CREATE TABLE test (id INT) ENGINE = InnoDB;
ERROR 1050 (42S01): Table '`test`.`test`' already exists

The MySQL error log shows us the following …

This week, we did some migrations from MariaDB 10.0 to Percona Server 5.6 at the IT department of a big German bank.

We were perfectly aware that since version 10.0 the MariaDB code base started to diverge slightly away from the MySQL and Percona Server code base which are still pretty close to each other.

Because of the Percona Server option enforce_storage_engine we wanted to do this migration.

We stopped the MariaDB 10.0 server, replaced the binaries by the Percona Server 5.6 binaries, and started the …

Sometimes it could be desirable to replicate from a Galera Cluster to a single MySQL slave or to an other Galera Cluster. Reasons for this measure could be:

• An unstable network between two Galera Cluster locations.
• A separation of a reporting slave and the Galera Cluster so that heavy reports on the slave do not affect the Galera Cluster performance.
• Mixing different sources in a slave or a Galera Cluster (fan-in replication).

This article is based on earlier research work (see MySQL Cluster - Cluster …

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Hello,

there are companies which earn tens of thousands of Euros per hour with their MySQL databases. Other companies operate their ERP system on MySQL, to which 1000 employees are attached to. Is the database down 1000 people are not working any more until the system is working again! Downtime costs starting at EUR 30'000.- per hour upwards.

Support through the MySQL specialists?

These companies have properly planned operations of their MySQL databases, designed their production systems redundantly and …

Thanks, Morgan!

MySQL single query performance - the truth!

As suggested by morgo I did a little test for the same query and the same data-set mentioned in Impact of column types on MySQL JOIN performance but looking into an other dimension: the time (aka MySQL versions).

The answer

To make it short. As a good consultant the answer must be: “It depends!” :-)

The test

The query was again the following:

SELECT *
  FROM a
  JOIN b ON b.a_id = a.id
 WHERE a.id BETWEEN 10000 AND 15000
;

The Query Execution Plan was …

Hi Morgan,

Thanks!

I have planed such a test already a while ago but did not find the time to do it yet...

In my mind I have some numbers showing that since MySQL 4.0 single query performance has decreased significantly...

This leads to the question: Where are all the MySQL branches and forks heading to and is this in the interest of the majority of the MySQL users or just in the interest of a few ones like Facebook, LinkeId, Google, Booking.com etc...?

Regards,
Oli

In our MySQL trainings and consulting engagements we tell our customers always to use the smallest possible data type to get better query performance. Especially for the JOIN columns. This advice is supported as well by the MySQL documentation in the chapter Optimizing Data Types:

Use the most efficient (smallest) data types possible. MySQL has many specialized types that save disk space and memory. For example, use the smaller integer types if possible to get smaller tables. MEDIUMINT is often a better …

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Features

Galera is a synchronous multi-master replication Cluster for MySQL/InnoDB databases, having features like:

• Synchronous replication
• Active-active multi-master topology
• Read and write to any cluster node
• Automatic membership control, failed nodes drop from the cluster
• Automatic node joining
• True parallel replication, on row level
• Direct client connections, native MySQL look & feel

Benefits

The benefits of these features are:

• No slave lag
• No lost transactions
• Read scalability and write …

Hello csmanioto,

As mentioned above this is a PoC and should never be used on system with critical data because it is an evil hack!!!

If you would like to see this comming in production soon you should vote fore this feature request.

Great News: Galera Cluster v3.1 GA for MySQL 5.6 was released at Percona Live London (PLUK) 2013. The information is still a bit hidden…

You can find it here:

• The Plugin: https://launchpad.net/galera/3.x/25.3.1
• The MySQL: https://launchpad.net/codership-mysql/5.6/5.6.14-25.1

Or directly on our download page.

Careful: Online-Upgrade from 5.5 to 5.6 will not work yet. We have to find a work-around…

We had a Galera Cluster support case recently. The customer was drenched in tears because his Galera Cluster did not work any more and he could not make it work any more.

Upsss! What has happened?

A bit of the background of this case: The customer wanted to do a rolling-restart of the Galera Cluster under load because of an Operating System upgrade which requires a reboot of the system.

Lets have a look at the MySQL error log to see what was going on. Customer restarted server with NodeC:

12:20:42 NodeC: …

Hello thatsafunnynamecomment,

Thanks for reading and correcting my findings! You are absolutely right. I did a bit short-cut too much in maths!

For your comment #2 it looks like I did not investigate carefully enough. Thanks for correcting me. I found several sources pointing to tcp_fin_timeout and mentioned TIME_WAIT is affected. So I should just be more careful next time. Especially in a domain I am an absolute noob.

Shinguz

In MySQL we have the typical behaviour that we open and close connections very often and rapidly. So we have very short-living connections to the server. This can lead in extreme cases to the situation that the maximum number of TCP ports are exhausted.

The maximum number of TCP ports we can find with:

# cat /proc/sys/net/ipv4/ip_local_port_range
32768   61000

In this example we can have in maximum (61000 - 32768 = 28232) connections concurrently open.

When a TCP connections closes the port cannot be …