Dear Xavi,
How do I test the locks, for example locks for write fop. I have two clients(independent), both are trying to write to same file.
1. According to my understanding, both can successfully write if the offsets don't overlap . I mean, the WRITE FOP takes a chunk lock on the file . As
long as the clients don't try to write to the same chunk, it should be OK. If no locks present, it can lead to inconsistency.
2. Different FOPs can always run simultaneously. (Example WRITE and READ FOPs, or two READ FOPs).
3. WRITE & some metadata FOP (like setattr) together . Cannot happen together with locks , even though chances are very low.
Pls. clarify.
Best regards
JK
On Wed, Nov 30, 2016 at 5:49 PM, jayakrishnan mm <jayakrishnan.mm@xxxxxxxxx> wrote:
Hi Xavier,Thank you very much for your explanation. This helped me to understand more about locking in EC.Best RegardsJKOn Mon, Nov 28, 2016 at 4:17 PM, Xavier Hernandez <xhernandez@xxxxxxxxxx> wrote:Hi,
On 11/28/2016 02:59 AM, jayakrishnan mm wrote:
Hi Xavier,
Notice that EC xlator uses blocking locks. Any specific reason for this?
In a distributed filesystem like gluster a synchronization mechanism is a must to avoid data corruption.
Do you think this will affect the performance ?
Of course the need for locks has a performance impact, and we cannot avoid them to guarantee data integrity. However some optimizations have been applied, specially the eager locking which allows a lock to be reused without unlocking/locking again.
(In comparison AFR first tries non blocking locks and if not
successful, tries blocking locks then)
EC also tries a non-blocking lock first.
Also, why two locks are needed per FOP ? One for normal I/O and
another for self healing?
The only fop that currently needs two locks is 'rename', and only when source and destination directories are different. All other fops only take one lock at most.
Best regards,
Xavi
Best regards
JK
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