On Mon, Nov 12, 2018 at 10:39 AM Vijay Bellur <vbellur@xxxxxxxxxx> wrote:
On Sun, Nov 11, 2018 at 8:25 PM Raghavendra Gowdappa <rgowdapp@xxxxxxxxxx> wrote:On Sun, Nov 11, 2018 at 11:41 PM Vijay Bellur <vbellur@xxxxxxxxxx> wrote:On Mon, Nov 5, 2018 at 8:31 PM Raghavendra Gowdappa <rgowdapp@xxxxxxxxxx> wrote:On Tue, Nov 6, 2018 at 9:58 AM Vijay Bellur <vbellur@xxxxxxxxxx> wrote:On Mon, Nov 5, 2018 at 7:56 PM Raghavendra Gowdappa <rgowdapp@xxxxxxxxxx> 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?No. Perf benchmarking is a task pending on me.When can we expect this task to be complete?In any case, I don't think it is ideal for us to merge a patch without completing our due diligence on it. How do we want to handle this scenario since the patch is already merged?We could:1. Revert the patch now2. Review the performance data and revert the patch if performance characterization indicates a significant dip. It would be preferable to complete this activity before we branch off for the next release.
I am for option 2. Considering the branch out for next release is another 2 months, and no one is expected to use the 'release' off a master branch yet, it makes sense to give that buffer time to get this activity completed.
Regards,
Amar
_______________________________________________3. Think of some other option?Thanks,Vijay
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Amar Tumballi (amarts)
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