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Displaying posts with tag: howto (reset)
Debugging MySQL Cluster installed using RPMs using gdb

This post explains how to debug MySQL Cluster 7.1, installed using the RPM packages, using gdb on a Linux box (Red Hat, Oracle Enterprise Linux, CentOS, ..).

When a data node crashes lots of information goes into the error log, trace files and out log. However, it makes sometimes sense when you can repeat the crash, to run the data node in debug mode, or using gdb.

First, using RPMs and a Linux distribution, make sure you have the ‘debuginfo’ package installed. For example, for Red Hat or Oracle Enterprise Linux on a 64-bit machine, this package would be called: MySQL-Cluster-gpl-debuginfo-7.1.15-1.rhel5.x86_64.rpm .

Create a file with the following commands, we will name it ‘ndbd.gdb’:

set pagination off
set logging overwrite on
set logging file …
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MySQL Cluster: Rotating the log file of the Data Nodes

There is a log file called ndb_<NodeID>_out.log created by the MySQL Cluster data nodes which can become quite big overtime. There is, unlike the cluster logs created by the management nodes, no rotation build in. So you have to revert to the basics and copy the file away, truncating the old one.

For example, if you want to ‘rotate’ the log file of data node with NodeID 3:

shell> mv ndb_3_out.log.1.gz ndb_3_out.log.2.gz
shell> cp ndb_3_out.log ndb_3_out.log.1
shell> cat /dev/null > ndb_3_out.log
shell> gzip ndb_3_out.log.1

It’s not elegant, and you might lose some entries, but it will help you keeping disk usage minimal. If you don’t need the log at all, just line 3 would do the trick.

You can use logrotate‘s copytruncate to …

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Refactored: Poor man’s MySQL replication monitoring

This is a reply to the blog post Poor man’s MySQL replication monitoring. Haidong Ji had a few problems using MySQLdb (could use the ‘dict’ cursor) and apparently he doesn’t want to much dependencies. I agree that using the mysql client tool is a nice alternative if you don’t want to use any 3rd party Python modules. And the MySQL client tools are usually and should be installed with the server.

However, since MySQL Connector/Python only needs itself and Python, dependencies are reduced to a minimum. Here …

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Custom logger for your MySQL Cluster data nodes

The MySQL Cluster data node log files can become very big. The best solution is to actually fix the underlying problem. But if you know what you are doing, you can work around it and filter out these annoying log entries.

An example of ‘annoying’ entries is when you run MySQL Cluster on virtual machines (not good!) and disks and OS can’t follow any more; a few lines from the ndb_X_out.log:

2011-04-03 10:52:31 [ndbd] WARNING  -- Ndb kernel thread 0 is stuck in: Scanning Timers elapsed=100
2011-04-03 10:52:31 [ndbd] INFO     -- timerHandlingLab now: 1301820751642 sent: 1301820751395 diff: 247
2011-04-03 10:52:31 [ndbd] INFO     -- Watchdog: User time: 296  System time: 536
2011-04-03 10:52:31 [ndbd] INFO     -- Watchdog: User time: 296  System time: 536
2011-04-03 10:52:31 [ndbd] WARNING  -- Watchdog: …
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MySQL Semi-Synchronous Replication. See the Magic. Try the Magic.

Overview MySQL Replication is one of the most used and valued features of the MySQL Server. Unlike some other products on the market, it’s out-of-the-box, easy to configure, non-paid and smart features. Most of our medium/large/super-large installation base are using replication to achieve “scale-out” scaling. Some will use it for backup purposes (not as HA [...]

MySQL Enterprise Backup 3.5, the crash course

Every ones loves hands-on tutorials with code snippets and stuff to establish the knowledge that something can be done. So here is my first one; MySQL Enterprise Backup 3.5. The new and shiny backup solution for MySQL. Our clients, for a long time, are asking for an enterprise ready, stable, safe, quick, easy, feature rich, [...]

Setting client flags with MySQL Connector/Python

Setting client flags with MySQL Connector/Python works a bit differently than the other MySQL Python drivers. This blog post describes how to set and unset flags, like the CLIENT_FOUND_ROWS.

The default client flags for the MySQL Client/Server protocol can be retrieved using the constants.ClientFlag class:

>>> from mysql.connector.constants import ClientFlag
>>> defaults = ClientFlag.get_default()
>>> print ClientFlag.get_bit_info(defaults)

To set an extra flag when connecting to MySQL you use the client_flags argument of connect()-method. For example, you’d like to have the …

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Query caching with MySQL Connector/Python

This blog post shows how to create a cursor class for MySQL Connector/Python which will allow you to cache queries. It will hold the query itself and the result in a global variable.

Note: this is a proof of concept and is only meant as a demonstration on how to extend MySQL Connector/Python.

Why query caching?

You are doing lots of queries that have the same result. It would be expensive to always run the same exact query. MySQL has already a query cache, and there is also memcached. But you like MySQL Connector/Python so much you’d like to do it yourself.

A cursor caching queries and their result

To demonstrate a simple implementation of a query cache, we inherit …

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Buffering results with MySQL Connector/Python

MySQL Connector/Python doesn’t buffer results by default. This means you have to fetch the rows when you issued a SELECT. This post describes how you can change this behavior.

Why buffering result sets?

Buffering or storing the result set on the client side is handy when you, for example, would like to use multiple cursors per connection and you’de like to traverse each one interleaved.

Keep in mind that with bigger result sets, the client side will use more memory. You just need to find out for yourself what’s best. When you know result sets are mostly small, you might opt to buffer.

MySQLdb by default buffers results and you need to use a different cursor to disable it. oursql does not buffer by default. This is good to …

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Fetching rows as dictionaries with MySQL Connector/Python

This post describes how to make a custom cursor returning rows as dictionaries using MySQL Connctor/Python v0.2 (or later).

Problem: you want to fetch rows from the database and return them as a dictionary with keys being the column names.

First, lets check how you would do it without any custom cursor.

cnx = mysql.connector.connect(host='localhost',database='test')
cur = cnx.cursor()
cur.execute("SELECT c1, c2 FROM t1")
result = []
columns = tuple( [d[0].decode('utf8') for d in cur.description] )
for row in cur:
  result.append(dict(zip(columns, row)))

The above results in an output like this:

[python light="true"]
[{u'c1': datetime.datetime(2010, 10, 13, 8, 55, 35), u'c2': u'ham'},
 {u'c1': datetime.datetime(2010, 10, …
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Showing entries 31 to 40 of 55
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