On Mon, Jan 5, 2015 at 1:25 PM, Michael Paquier
<michael.paqu...@gmail.com> wrote:
> On Thu, Jan 1, 2015 at 1:10 AM, Robert Haas <robertmh...@gmail.com> wrote:
>> On Mon, Dec 29, 2014 at 6:14 AM, Heikki Linnakangas
>> <hlinnakan...@vmware.com> wrote:
>>> Hmm. There is no way to check beforehand if a palloc() will fail because of
>>> OOM. We could check for MaxAllocSize, though.
>> I think we need a version of palloc that returns NULL instead of
>> throwing an error.  The error-throwing behavior is for the best in
>> almost every case, but I think the no-error version would find enough
>> users to be worthwhile.
> Compression is one of those areas, be it compression of WAL or another
> type. The new API would allow to fallback to the non-compression code
> path if buffer allocation for compression cannot be done because of an
> OOM.
> FWIW, I actually looked at how to do that a couple of weeks back, and
> you just need a wrapper function, whose content is the existing
> AllocSetAlloc, taking an additional boolean flag to trigger an ERROR
> or leave with NULL if an OOM appears. On top of that we will need a
> new method in MemoryContextMethods, let's call it alloc_safe, for its
> equivalent, the new palloc_safe.

MemoryContextAllocExtended() was added, so isn't it time to replace palloc()
with MemoryContextAllocExtended(CurrentMemoryContext, MCXT_ALLOC_NO_OOM)
in allocate_recordbuf()?


Fujii Masao
*** a/src/backend/access/transam/xlogreader.c
--- b/src/backend/access/transam/xlogreader.c
*** 149,155 **** allocate_recordbuf(XLogReaderState *state, uint32 reclength)
  	if (state->readRecordBuf)
! 	state->readRecordBuf = (char *) palloc(newSize);
  	state->readRecordBufSize = newSize;
  	return true;
--- 149,163 ----
  	if (state->readRecordBuf)
! 	state->readRecordBuf =
! 		(char *) MemoryContextAllocExtended(CurrentMemoryContext,
! 											newSize,
! 											MCXT_ALLOC_NO_OOM);
! 	if (state->readRecordBuf == NULL)
! 	{
! 		state->readRecordBufSize = 0;
! 		return false;
! 	}
  	state->readRecordBufSize = newSize;
  	return true;
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