On 24/06/14 17:37, Alexandre DERUMIER wrote:
Hi Greg,
So the only way to improve performance would be to not use O_DIRECT (as this
should bypass rbd cache as well, right?).
yes, indeed O_DIRECT bypass cache.
BTW, Do you need to use mysql with O_DIRECT ? default innodb_flush_method is
fdatasync, so it should work with cache.
(but you can lose some write is case of a crash failure)
While this suggestion is good, I don't believe that the "you could lose
data" statement is correct with respect to fdatasync (or fsync) [1].
With all modern kernels I think you will find that fdatasync will
actually flush modified buffers to the device (i.e write through file
buffer cache).
All of which means that Mysql performance (looking at you binlog) may
still suffer due to lots of small block size sync writes.
regards
Mark
[1] See kernel archives concerning REQ_FLUSH and friends.
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