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.
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).
* atime consistency. ctime generator offers atime consistency equivalent to noatime mounts. But, with my limited experience I've not seen too many usecases that require atime consistency. If you've a usecase please point it out and we'll think how we can meet that requirement.
[1] https://review.gluster.org/#/c/glusterfs/+/21060/
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1600923
[3] https://bugzilla.redhat.com/show_bug.cgi?id=1617972
[4] https://bugzilla.redhat.com/show_bug.cgi?id=1393743
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1600923
[3] https://bugzilla.redhat.com/show_bug.cgi?id=1617972
[4] https://bugzilla.redhat.com/show_bug.cgi?id=1393743
regards,
Raghavendra
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