Re: Straightforward changes for increased SMP scalability

Simon Riggs wrote:

> Proposals
>
> 1. For the first result, I suggest that we introduce some padding into
> the shmem structure XLogCtlData to alleviate false sharing that may
> exist between holders of WALInsertLock, WALWriteLock and info_lck. The
> cost of this will be at most about 200 bytes of shmem, with a low risk
> change. The benefits are hard to quantify, but we know this is an area
> of high contention and we should do all we can to reduce that.
> This hasn't been discussed previously, though we have seen good benefit
> from avoiding false sharing in other cases, e.g. LWLOCK padding.
>
> 2. Increase NUM_BUFFER_PARTITIONS from 16 to 256 (or higher).
> This has been discussed previously:
> http://archives.postgresql.org/pgsql-hackers/2006-09/msg00967.php
>
> Both of these changes are simple enough to consider for 8.3
>
> Comments?

+1 on the idea (I can speak to the technical side). What I can say is
that it is pretty much known that after 8 cores we slow down. Although
8.2 is better than any other release in this regard.

Joshua D. Drake

>

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