Re: pgsql: Fix bug leading to restoring unlogged relations from empty files

Coverity is complaining that in

void
FlushOneBuffer(Buffer buffer)
{
BufferDesc *bufHdr;

/* currently not needed, but no fundamental reason not to support */
Assert(!BufferIsLocal(buffer));

Assert(BufferIsPinned(buffer));

bufHdr = GetBufferDescriptor(buffer - 1);

LWLockHeldByMe(bufHdr->content_lock);

FlushBuffer(bufHdr, NULL);
}

the call to LWLockHeldByMe() is useless.

On 12/10/15 10:50 AM, Andres Freund wrote:
> Fix bug leading to restoring unlogged relations from empty files.
>
> At the end of crash recovery, unlogged relations are reset to the empty
> state, using their init fork as the template. The init fork is copied to
> the main fork without going through shared buffers. Unfortunately WAL
> replay so far has not necessarily flushed writes from shared buffers to
> disk at that point. In normal crash recovery, and before the
> introduction of 'fast promotions' in fd4ced523 / 9.3, the
> END_OF_RECOVERY checkpoint flushes the buffers out in time. But with
> fast promotions that's not the case anymore.
>
> To fix, force WAL writes targeting the init fork to be flushed
> immediately (using the new FlushOneBuffer() function). In 9.5+ that
> flush can centrally be triggered from the code dealing with restoring
> full page writes (XLogReadBufferForRedoExtended), in earlier releases
> that responsibility is in the hands of XLOG_HEAP_NEWPAGE's replay
> function.
>
> Backpatch to 9.1, even if this currently is only known to trigger in
> 9.3+. Flushing earlier is more robust, and it is advantageous to keep
> the branches similar.
>
> Typical symptoms of this bug are errors like
> 'ERROR: index "..." contains unexpected zero page at block 0'
> shortly after promoting a node.
>
> Reported-By: Thom Brown
> Author: Andres Freund and Michael Paquier
> Discussion: 20150326175024(dot)GJ451(at)alap3(dot)anarazel(dot)de
> Backpatch: 9.1-
>
> Branch
> ------
> REL9_5_STABLE
>
> Details
> -------
> http://git.postgresql.org/pg/commitdiff/5b51805fe4b9fec95274924c5733093a5f685a58
>
> Modified Files
> --------------
> src/backend/access/transam/xlogutils.c | 9 +++++++++
> src/backend/storage/buffer/bufmgr.c | 21 +++++++++++++++++++++
> src/include/storage/bufmgr.h | 1 +
> 3 files changed, 31 insertions(+)
>
>