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10 Newer Entries Showing entries 31 to 33

Displaying posts with tag: yves (reset)

Logging all the queries with MySQL 5.0
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With MySQL 5.1, getting and analyzing all the queries hitting the database is very easy even if you don’t have access to the MySQL enterprise Monitor.  You can either activate the general log or, my favourite option, activate the slow query log with a sub millisecond long query time. Long query time below one second is an option introduced in MySQL 5.1. In order to catch all the queries, you will also need to disable the query cache.  The main advantages of the slow query log over the general log is that you have access to more information like the query time, the lock time, the number of rows examined and the number of rows sent back.  All the options surrounding the slow query log in MySQL 5.1 are dynamic so it is easy to turn the logging ON and OFF.  Once you have the queries, tools, like mysqlsla, can be used to anlyzed the queries and group them by type.

All these tips are nice if you are using

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e1000 InterruptThrottleRate
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The e1000 Nic is very common and can be found in many servers.  During my last NBD cluster engagement, on a set of 5 Dell 1950 servers equipped with a quad e1000 Nic, we were trying to tune cluster performance and one of the thing that was disapointing was that the system time, to processed interrupts from the Nics, was always low.  Since neither the ndbd processes or the mysqld processes were using a significant amount of CPU, we were wondering where the bottleneck was.

Then, Michel Donais, from the client, read the Linux driver documentation and bingo!!! Those e1000 Nics throttle interrupts by default at 8000/s.  8000… it is a big limiting factor….   design to prevent DOS attacks.  We removed the throttling and… reach more than 30,000 interrupt/s and guess what, the number of transaction per second scaled with it along with the ndbd and mysqld cpu usage.  Interesting isn’t it?

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NDB Cluster and Max_rows
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Just before Christmas, I was working with a client that needed to insert more than a billion rows into a NDB table. The cluster was big,
14 nodes, and after a few hundred millions rows, we got the following error:

2008-12-09 18:28:52 [ndbd] INFO     -- dbacc/DbaccMain.cpp
2008-12-09 18:28:52 [ndbd] INFO     -- DBACC (Line: 5274) 0x0000000e
2008-12-09 18:28:52 [ndbd] INFO     -- Error handler shutting down system
2008-12-09 18:28:53 [ndbd] INFO     -- Error handler shutdown completed - exiting
2008-12-09 18:28:56 [ndbd] ALERT    -- Node 10: Forced node shutdown completed. Caused by error 2304: 'Array index out of range(Internal error, programming error or missing error message,

which looks like a bug in the NDB kernel.  In fact, it is not really a bug.  This error is the equivalent of a “table too large” error










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10 Newer Entries Showing entries 31 to 33

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