[Bugs] [Bug 1439731] Sharding: Fix a performance bug

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1439731

Krutika Dhananjay <kdhananj at redhat.com> changed:

           What    |Removed                     |Added
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           Doc Type|If docs needed, set a value |Bug Fix


--- Doc Text *updated* ---
Cause: 
A bug in shard's in-memory cache invalidation in STAT fop was causing it to send lot of LOOKUPs as part of cache-invalidation, even when the file was not undergoing any modification.

Consequence: 
This was causing every STAT call from the application to be followed by a LOOKUP, leading to sub-optimal performance of IO on the VMs.

Fix: 
In-memory cache invalidation in shard's STAT operation was corrected.

Result: 
Now with the fix, in a pure-read workload, there wasn't as many LOOKUPs as the number of STATs, leading to improved VM performance. This also benefited performance in mixed read-write workload from the VMs.


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