PostgreSQL performance scaling
ivoras at freebsd.org
Tue Nov 23 00:30:08 UTC 2010
On 11/22/10 17:37, David Xu wrote:
> Mark Felder wrote:
>> I recommend posting this on the Postgres performance list, too.
> I think if PostgreSQL uses semaphore for inter-process locking,
> it might be a good idea to use POSIX semaphore exits in our head
> branch, the new POSIX semaphore implementation now supports
> process-shared, and is more light weight than SYSV semaphore,
> if there is no contention, a process need not enter kernel to
> acquire/release a lock. Note that I have just fixed a bug in head
> branch. However RELENG_8 does not support process-shared semaphore
Another thing might be that, despite that they appear to try to avoid
it, they possibly have a large number of processes hanging on the same
semaphore, leading to thundering herd problem.
There already is code for POSIX semaphores in PostgreSQL. It requires
some manual fiddling with the configuration to enable
However, I've just tried it on 9-CURRENT and it doesn't work:
Nov 23 01:23:02 biggie postgres: [1-1] FATAL: sem_init failed: No
space left on device
PostgreSQL calls it as "sem_init(sem, 1, 1);"
One more thing: apparently I had to kldload sem.ko - which looks like an
error, since it is in GENERIC in 8-STABLE !
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