On 2013/6/17 18:59, Robert van Leeuwen wrote:
I'm facing the issue about the performance degradation, and once I glanced that
changing the value in /proc/sys
/vm/vfs_cache_pressure will do a favour.
Can anyone explain to me whether and why it is useful?
Hi,
When this is set to a lower value the kernel will try to keep the inode/dentry
cache longer in memory.
Since the swift replicator is scanning the filesystem continuously it will eat
up a lot of iops if those are not in memory.
To see if a lot of cache misses are happening, for xfs, you can look at
xs_dir_lookup and xs_ig_missed.
( look at http://xfs.org/index.php/Runtime_Stats )
We greatly benefited from setting this to a low value but we have quite a lot
of files on a node ( 30 million)
Note that setting this to zero will result in the OOM killer killing the
machine sooner or later.
(especially if files are moved around due to a cluster change ;)
Cheers,
Robert van Leeuwen
Hi,
We set this to a low value(20) and the performance is better than
before. It seems quite useful.
According to your description, this issue is related with the
object quantity in the storage. We delete all the objects in the storage
but it doesn't help anything. The only method to recover is to format
and re-mount the storage node. We try to install swift on different
environment but this degradation problem seems to be an inevitable one.
Cheers,
Jonathan Lu
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