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Add assert to WALReadFromBuffers().

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Per suggestion from Andres.

Discussion: https://postgr.es/m/20240214025508.6mcblauossthvaw3@awork3.anarazel.de
This commit is contained in:
Jeff Davis 2024-02-16 10:35:42 -08:00
parent 5497daf3aa
commit 9ecbf54075
1 changed files with 6 additions and 18 deletions
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24
src/backend/access/transam/xlog.c
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@ -1710,12 +1710,13 @@ GetXLogBuffer(XLogRecPtr ptr, TimeLineID tli)
* of bytes read successfully. * of bytes read successfully.
* *
* Fewer than 'count' bytes may be read if some of the requested WAL data has * Fewer than 'count' bytes may be read if some of the requested WAL data has
* already been evicted from the WAL buffers, or if the caller requests data * already been evicted.
* that is not yet available.
* *
* No locks are taken. * No locks are taken.
* *
* The 'tli' argument is only used as a convenient safety check so that * Caller should ensure that it reads no further than LogwrtResult.Write
* (which should have been updated by the caller when determining how far to
* read). The 'tli' argument is only used as a convenient safety check so that
* callers do not read from WAL buffers on a historical timeline. * callers do not read from WAL buffers on a historical timeline.
*/ */
Size Size
@ -1724,26 +1725,13 @@ WALReadFromBuffers(char *dstbuf, XLogRecPtr startptr, Size count,
{ {
char *pdst = dstbuf; char *pdst = dstbuf;
XLogRecPtr recptr = startptr; XLogRecPtr recptr = startptr;
XLogRecPtr upto; Size nbytes = count;
Size nbytes;
if (RecoveryInProgress() || tli != GetWALInsertionTimeLine()) if (RecoveryInProgress() || tli != GetWALInsertionTimeLine())
return 0; return 0;
Assert(!XLogRecPtrIsInvalid(startptr)); Assert(!XLogRecPtrIsInvalid(startptr));
Assert(startptr + count <= LogwrtResult.Write);
/*
* Don't read past the available WAL data.
*
* Check using local copy of LogwrtResult. Ordinarily it's been updated by
* the caller when determining how far to read; but if not, it just means
* we'll read less data.
*
* XXX: the available WAL could be extended to the WAL insert pointer by
* calling WaitXLogInsertionsToFinish().
*/
upto = Min(startptr + count, LogwrtResult.Write);
nbytes = upto - startptr;
/* /*
* Loop through the buffers without a lock. For each buffer, atomically * Loop through the buffers without a lock. For each buffer, atomically