[Gluster-users] On making ctime generator enabled by default in stack

Vijay Bellur vbellur at redhat.com
Sun Nov 11 18:10:56 UTC 2018

On Mon, Nov 5, 2018 at 8:31 PM Raghavendra Gowdappa <rgowdapp at redhat.com>

> On Tue, Nov 6, 2018 at 9:58 AM Vijay Bellur <vbellur at redhat.com> wrote:
>> On Mon, Nov 5, 2018 at 7:56 PM Raghavendra Gowdappa <rgowdapp at redhat.com>
>> wrote:
>>> All,
>>> There is a patch [1] from Kotresh, which makes ctime generator as
>>> default in stack. Currently ctime generator is being recommended only for
>>> usecases where ctime is important (like for Elasticsearch). However, a
>>> reliable (c)(m)time can fix many consistency issues within glusterfs stack
>>> too. These are issues with caching layers having stale (meta)data
>>> [2][3][4]. Basically just like applications, components within glusterfs
>>> stack too need a time to find out which among racing ops (like write, stat,
>>> etc) has latest (meta)data.
>>> Also note that a consistent (c)(m)time is not an optional feature, but
>>> instead forms the core of the infrastructure. So, I am proposing to merge
>>> this patch. If you've any objections, please voice out before Nov 13, 2018
>>> (a week from today).
>>> As to the existing known issues/limitations with ctime generator, my
>>> conversations with Kotresh, revealed following:
>>> * Potential performance degradation (we don't yet have data to
>>> conclusively prove it, preliminary basic tests from Kotresh didn't indicate
>>> a significant perf drop).
>> Do we have this data captured somewhere? If not, would it be possible to
>> share that data here?
> I misquoted Kotresh. He had measured impact of gfid2path and said both
> features might've similar impact as major perf cost is related to storing
> xattrs on backend fs. I am in the process of getting a fresh set of
> numbers. Will post those numbers when available.

I observe that the patch under discussion has been merged now [1]. A quick
search did not yield me any performance data. Do we have the performance
numbers posted somewhere?


[1] https://review.gluster.org/#/c/glusterfs/+/21060/
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