[Gllug] Painfully slow MySql performance on 64-bit Atom processor

[Richard Huxton]

On 18/01/11 19:52, John Winters wrote:
>
> I've since done some more reading and the essential difference
> apparently is that ext3 defaults to "barrier=0" and ext4 defaults to
> "barrier=1". Still not quite sure what it means though.

This is enabling "write barriers". Writes before a barrier is guaranteed 
to be written to real, magnetic physical disk before writes after it. 
Otherwise you can end up with a mix of multiple journal updates and 
file-block updates getting partially written to disk with a crash.

http://en.wikipedia.org/wiki/Ext3#No_checksumming_in_journal
http://www.linuxtopia.org/online_books/rhel6/rhel_6_storage_admin/rhel_6_storage_writebarr.html

Contrary to what you might think, this is less useful for databases than 
other applications. RDBMs tend to handle their own transaction logs 
carefully anyway.

-- 
   Richard Huxton
   Archonet Ltd
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