On Mon, Jan 5, 2015 at 1:25 PM, Michael Paquier
<[email protected]> wrote:
> On Thu, Jan 1, 2015 at 1:10 AM, Robert Haas <[email protected]> wrote:
>> On Mon, Dec 29, 2014 at 6:14 AM, Heikki Linnakangas
>> <[email protected]> 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()?
Regards,
--
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)
pfree(state->readRecordBuf);
! state->readRecordBuf = (char *) palloc(newSize);
state->readRecordBufSize = newSize;
return true;
}
--- 149,163 ----
if (state->readRecordBuf)
pfree(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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