MySQL Tech-Feed (en)

Our Advanced MySQL Developer Workshop is over now and IMHO it was quite a success.
During the workshop it is planned to have some exercises. If you are curious and if you want to test or train your MySQL skills, find the exercises here: Advanced MySQL Developer Workshop Exercises.

The solutions are available on request as well.

If you like those exercises we could also provide the exercises of our Advanced MySQL DBA Workshop. Please let us know if you are interested in…

Have fun.

Abstract: In this article we provide a little JMeter WebShop Example Benchmark for MySQL.

For our Advanced MySQL Developer Workshop we have one exercise Benchmarking MySQL with JMeter. For this exercise we are using the FoodMart-2.0
[1
] Schema and simulating a simple WebShop Transaction:

• Logging in
• Put some articles into the basket
• Buy the articles
• Log out

I found it pretty hard to find good and detailed examples how to do this with JMeter and I wasted a lot of time searching and figuring out how it …

Abstract: In this article we have a look at the compression options of common zipping tools and its impact on the size of the compressed files and the compression time. Further we look at the new parallel zip tools which make use of several cores.

Start with a backup first

From time to time I get into the situation where I have to compress some database files. This happens usually when I have to do some recovery work on customers systems. Our rule number 1 before starting with a recovery is: Do a file …

Abstract: In this article we discuss how big is the performance impact of MySQL TRIGGERs compared to application side logging (with INSERT) into a MySQL table.

What was in my mind from the past

A while ago when MySQL released its Stored Language features in v5.0 I have seen a book
[1
] about this topic. In this book was a performance comparison between different implementations of computational tasks, one was done in MySQL Stored Language. The result was, that MySQL Stored Language feature sucks also …

With the new MySQL 5.6 release there are some more InnoDB Data Dictionary Tables in the INFORMATION_SCHEMA:

New with MySQL 5.5 are:

New with MySQL 5.6 are:

Abstract: Heating up the InnoDB Buffer Pool during the MySQL instance startup should significantly improve InnoDB Performance in the beginning of the life of the Instance. This is achieved by sequential scans of the needed data instead of random I/O reads which would happen when we just let the system work it out by itself.
How to find the database objects which can be loaded during MySQL start-up and how to load them automatically is described in this article.

New Table in the INFORMATION_SCHEMA

Some of my …

Some people did not agree with my statements or had some questions…

A search using col_name IS NULL employs indexes if col_name is indexed. [1]

Some experiments on a table with a few (= 4) NULL values:

EXPLAIN SELECT * FROM t2 WHERE dt IS NULL;
+----+-------------+-------+------+---------------+------+---------+-------+------+-------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref   | rows | Extra       | …

Abstract:

It is common practice in MySQL table design that fields are declared as NOT NULL but some non-sense DEFAULT values are specified for unknown field contents. In this article we show why this behavior is non optimal an why you should better declare a field to allow NULL values and use NULL values instead of some dummy values.

What we can see often out in the field

Recently we had a discussion with a customer if it makes more sense to store a default value or NULL in InnoDB tables when we do not know …

One of our partners recently asked me on what platforms do we usually see MySQL installed out there…

The last 5 years I gave the answer: Typically it is 80% Linux, 10% Windows, 5% Solaris and 5% all others. But this was only the picture of my limited view and I was not sure how objective this was.

This time I really wanted to know it and so I collected the information of about 570 MySQL installations of customers.

The following numbers came out:

Operating System

We did recently a review of one of our customers systems and we found that the Query Cache was disabled even thought it had significant more read than write queries.
When we asked the customer why he has not enabled the Query Cache he mentioned a review that was done a few years ago and which stated that the Query Cache hit ratio was non optimal.
This was verified on a testing system which had the Query Cache enabled by accident.

But we all thought that the Query Cache would make sense in this situation so …

When we analyze our customers systems we see typically a high fragmentation of the query cache after a while. This leads to a less optimal use of the Query Cache than possible.

With the following Query you can see the values for your Query Cache:

mysql> SHOW GLOBAL STATUS LIKE 'Qcache%';
+-------------------------+----------+
| Variable_name           | Value    |
+-------------------------+----------+
| Qcache_free_blocks      | 11328    |
| Qcache_free_memory      | 89442000 |
| Qcache_hits …

We have just released v0.7.1 of the FromDual MySQL Performance Monitor. The new release can be downloaded from here.

In all editions some error messages have been cleaned-up, the fall-back data gather method mysql has been removed and the Maria SE template has been renamed to Aria.

In the edition dedicated to our customers most of the InnoDB graphs which are available with MEM v2.3.3 have been implemented now.

Please let us know, what you want to have monitored in addition and send us your feedback and …

A customer rose a support case with a problem on his Master-Master set-up. The 2^nd Master claims to have a problem:

master2> SHOW SLAVE STATUS<br>G
                ...
    Master_Log_File: master1-bin.000014
Read_Master_Log_Pos: 97975045
   Slave_IO_Running: No
  Slave_SQL_Running: Yes
Exec_Master_Log_Pos: 97975045
      Last_IO_Errno: 1236
      Last_IO_Error: Got fatal error 1236 from master when reading data from
                     binary log: 'Client requested master to start replication …

Today the German speaking MySQL User Group (DMySQLAG) was officially founded in Berlin. The association advocates:

• the information of the use, the handling and the experience with MySQL and development in the MySQL Eco-System as well as systems which use MySQL.
• the exchange of experience between MySQL users about MySQL and other systems.
• the Advice and Cooperation with Oracle and vendors of other systems.
• the submission of suggestions of the members to Oracle and vendors of other systems.

The intention of …

In our last customer project we had around 600 Gbyte of data in a MySQL database. Because this database consumed a significant amount of our disk space and backups with the InnoDB backup tool took pretty long we wanted to find out if we could get rid of some of the tables.

This application was growing over the last 10 years and it was not clear if some tables are still in use or not.

But how to find out when a table was touched last? MySQL/InnoDB theoretically could know about but does not report this …

A customer who is handling digital certificates had a problem with one of those. So we had to investigate.

Because the certificate is in binary form it is stored in a BLOB and we had to extract it from the database to do some verifications.

What first came to my mind was to extract the certificate with the SELECT INTO OUTFILE command. But the verification tool complained and told us that the certificate has a wrong format.

Luckily I found in the documentation the following statement: If you use INTO …

If you ask around about shared hosting setups with MySQL everybody is frightened. In fact it looks like shared hosting is one of the most difficult setups you can get.

The number of users is big, the number of tables huge and the load pattern is completely unpredictable and the queries often very, let us say: non-optimal.

Here one of the DBA wisdoms come into play: Controlling developers is like herding cats.

If you talk to the Shared MySQL Hoster they confirm that this setups are very demanding!

Why is …

In the following article I have summarized some steps and hints to set-up a MySQL active/passive failover Cluster also sometimes called MySQL HA.

With such a set-up you can achieve a 99.99% (4x9) HA set-up for MySQL (52 minutes downtime per year). The same procedure also works for PostgreSQL, Oracle and other database systems running on Linux (DRBD runs on Linux only).

The concept

The concept of an active/passive failover Cluster is the following:

• You have 2 servers (also called nodes).
• They communicate …

The FromDual Performance Monitor for MySQL has now a new module for monitoring DRBD. Since more an more of our customers want to run MySQL High Availability solutions based on DRBD we have implemented this module.

We gather all information which are reported with the command:

# cat /proc/drbd

version: 8.3.8 (api:88/proto:86-94)
 0: cs:Connected ro:Secondary/Primary ds:UpToDate/UpToDate C r----
    ns:1241240 nr:14311680 dw:15033532 dr:1241281 al:198 bm:52 lo:0 pe:0 ua:0
    ap:0 ep:1 wo:b oos:0

Now you …

Be careful when using SAN (Storage Area Networks) or similar shared storage solutions (and any other virtualization, consolidation or cloud solutions).

This week it happened again: A customer called us because he had some troubles with his on-line shop (note the date!). Everybody in his company complained that the databases are answering slowly.

When looking on the box (with iostat) we have seen some I/O load and some pending reads in InnoDB (SHOW ENGINE INNODB STATUS and SHOW GLOBAL STATUS LIKE …