Re: [PATCH] introduce XLogLockBlockRangeForCleanup()

On 13 June 2014 14:10, Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com> wrote:

> nbtxlog.c:btree_xlog_vacuum() contains the following comment:
>
> * XXX we don't actually need to read the block, we just need to
> * confirm it is unpinned. If we had a special call into the
> * buffer manager we could optimise this so that if the block is
> * not in shared_buffers we confirm it as unpinned.
>
> The attached patch introduces an XLogLockBlockRangeForCleanup() function
> that addresses this, as well as a "special call into the buffer manager"
> that makes it possible to lock the buffers without reading them.
>

In GetBufferWithoutRelcache(), I was wondering, rather than calling
PinBuffer(), if we do this :
LockBufHdr(buf);
PinBuffer_Locked(buf);
valid = ((buf->flags & BM_VALID) != 0);
then we can avoid having the new buffer access strategy BAS_DISCARD that is
introduced in this patch. And so the code changes in freelist.c would not
be necessary.

Will give further thought on the overall logic in
XLogLockBlockRangeForCleanup().

> will follow up with some performance numbers soon.
>

Yes, that would be nice.

-Amit