Hi,
I'm experimenting with using NFSv4 as storage for web servers and while
regular file access seems to work fine as soon as I bring flock() into
play things become more problematic.
I've create a tiny test php script that basically opens a file, locks it
using flock(), writes that fact into a log file (on a local filesystem),
performs a usleep(1000), writes into the log that it is about to unlock
the file and finally unlocks it.
I invoke that script using ab with a concurrency of 20 for a few
thousand requests.
The result is that while 99% of the request respond quickly a few
request seem to hang for up to 30 seconds. According to the log file
they must eventually succeed since I see all expected entries and the
locking seems to work as well since all entries are in the expected order.
Is it expected that these long delays happen? When I comment the locking
function out these hangs disappear.
Are there some knobs to tune NFS and make it behave better in these
situations?
Regards,
Dennis
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