Re: can the behaviour of LocalCheckPoint be changed ?

[Harrison Fisk]

Hi,

MySQL Cluster is currently an in-memory database. As a result of this, disk is only used in the event of a total cluster failure. So that means that normal transactions do not read or write to the disk.

The LocalCheckpoint mechanism is how it makes it possible to reuse REDO log space that is stored on disk. In order to safely remove the log records it needs to make sure that all corresponding data is written to disk. The way it does this is to write out all of the data. The reason this doesn't impact performance is because disk isn't used for normal operations (such as SELECT/INSERT). While this is occuring, you can still do all of the normal operations without affecting them at all.

Keep in mind that you can set how often it will do the LocalCheckPoint. If it is doing it for one row, then you can bump up the setting TimeBetweenLocalCheckpoints to cause it to wait for more data changes before doing it. The default is 4MB, so it shouldn't do it for just a single row (unless you changed it).

So no there is no way to change the behavior, but there isn't really any need as well. Normally if you get enough data to use up the REDO log space, you will want to make sure that it will be able to reuse the REDO log space when required, which requires the LocalCheckPoint to occur.

Let me know if you have any questions.

Harrison Fisk, Trainer and Consultant
MySQL AB, www.mysql.com