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.
Thanks,Vijay
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