[Gluster-users] GlusterFS behaviour on stat syscall with relatime activated

[Pranith Kumar Karampuri]

On 02/06/2016 12:19 AM, Simon Turcotte-Langevin wrote:
>
> Good day to you Pranith,
>
> Thank you for your answer, it was exactly this. However, we still have 
> an issue with RELATIME on GlusterFS.
>
> Stating the file does not modify atime anymore, with quick-read 
> disabled, however cat-ing the file does not replicate the atime.
>
This is because of open-behind feature. Disable open-behind with: 
"gluster volume set <volname> open-behind off". I believe you will see 
the atime behavior you want to see with it. This will reduce the 
performance of small file reads (< 64KB). Instead of one lookup over the 
network now it will do, lookup + open(This will be sent to both the 
replica bricks which updates atime) + read (Only one of the bricks). Let 
me know if you want any more information.

Pranith

> If I touch manually the file, the atime (or utimes) is replicated 
> correctly.
>
> So to sum it up:
>
> ·[node1] Touch –a file1
>
> oàAccess time is right on [node1] [node2] and [node3]
>
> ·[node1] Cat file1
>
> oàAccess time is right on [node1]
>
> oàAccess time is wrong on [node2] and [node3]
>
> Would you have any idea what is going on behind the curtain, and if 
> there is any way to fix that behavior?
>
> Thank you,
>
> Simon
>
> *From:*Pranith Kumar Karampuri [mailto:pkarampu at redhat.com]
> *Sent:* 5 février 2016 00:55
> *To:* Simon Turcotte-Langevin <simon.turcotte-langevin at ubisoft.com>; 
> gluster-users at gluster.org
> *Cc:* UPS_Development <UPS_Development at ubisoft.com>
> *Subject:* Re: [Gluster-users] GlusterFS behaviour on stat syscall 
> with relatime activated
>
> On 02/03/2016 10:12 PM, Simon Turcotte-Langevin wrote:
>
>     Hi, we have multiple clusters of GlusterFS which are mostly alike.
>     The typical setup is as such:
>
>     -Cluster of 3 nodes
>
>     -Replication factor of 3
>
>     -Each node has 1 brick, mounted on XFS with RELATIME and NODIRATIME
>
>     -Each node has 8 disks in RAID 0 hardware
>
>     The main problem we are facing is that observation of the access
>     time of a file on the volume will update the access time.
>
>     The steps to reproduce the problem are:
>
>     -Create a file (echo ‘some data’ > /mnt/gv0/file)
>
>     -Touch its mtime and atime to some past date (touch –d 19700101
>     /mnt/gv0/file)
>
>     -Touch its mtime to the current timestamp (touch –m /mnt/gv0/file)
>
>     -Stat the file until atime is updated (stat /mnt/gv0/file)
>
>     oSometimes it’s instant, sometimes it requires to execute the
>     above command a couple of time
>
> atime changes on open call.
>
> Quick-read xlator opens the file and reads the content on 'lookup' 
> which gets triggered in stat. It does that to serve reads from memory 
> to reduce number of network round trips for small files. Could you 
> disable that xlator and try the experiment? On my machine the time 
> didn't change after I disabled that feature using:
>
> "gluster volume set <volname> quick-read off"
>
> Pranith
>
>     On the IRC channel, I spoke to a developer (nickname ndevos) who
>     said that it might be a getxattr() syscall that could be called
>     when stat() is called on a replicated volume.
>
>     Anybody can reproduce this issue? Is it a bug, or is it working as
>     intended? Is there any workaround?
>
>     Thank you,
>
>     Simon
>
>
>
>
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