Re: Further XLogInsert scaling tweaking

Bruce Momjian wrote:
> 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

> > - 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?

We have LWLockPadded in lwlock.c; it only adjusts the size of the struct
to be a power of 2.

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Álvaro Herrera http://www.2ndQuadrant.com/
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