Re: Further XLogInsert scaling tweaking

On Mon, Sep 2, 2013 at 10:14:03AM +0300, Heikki Linnakangas wrote:
> diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
> index 39c58d0..28e62ea 100644
> --- a/src/backend/access/transam/xlog.c
> +++ b/src/backend/access/transam/xlog.c
> @@ -428,8 +428,14 @@ typedef struct XLogCtlInsert
> uint64 CurrBytePos;
> uint64 PrevBytePos;
>
> - /* insertion slots, see above for details */
> - XLogInsertSlotPadded *insertSlots;
> + /*
> + * Make sure the above heavily-contended spinlock and byte positions are
> + * on their own cache line. In particular, the RedoRecPtr and full page
> + * write variables below should be on a different cache line. They are
> + * read on every WAL insertion, but updated rarely, and we don't want
> + * those reads to steal the cache line containing Curr/PrevBytePos.
> + */
> + char pad[128];

Do we adjust for cache line lengths anywhere else? PGPROC? Should it
be a global define?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +