Update WAL buffers when restoring WAL at compute needed for LR (#324)

* Update WAL buffers when restoring WAL at compute needed for LR

* Fix copying data in WAL buffers

---------

Co-authored-by: Konstantin Knizhnik <[email protected]>

Author: 2 people

src/backend/access/transam/xlog.c

@@ -9287,3 +9287,29 @@ SetWalWriterSleeping(bool sleeping)
 	XLogCtl->WalWriterSleeping = sleeping;
 	SpinLockRelease(&XLogCtl->info_lck);
 }
+
+void
+XLogUpdateWalBuffers(char* data, XLogRecPtr start, size_t len)
+{
+	XLogRecPtr end;
+	int idx;
+	XLogRecPtr pagebegptr;
+
+	LWLockAcquire(WALBufMappingLock, LW_EXCLUSIVE);
+
+	end = start + len;
+	idx = XLogRecPtrToBufIdx(end);
+	pagebegptr = XLogCtl->xlblocks[idx] - XLOG_BLCKSZ;
+
+	if (pagebegptr + XLOG_BLCKSZ >= end && pagebegptr < end)
+	{
+		/* Last page of the segment is present in WAL buffers */
+		char* page = &XLogCtl->pages[idx * XLOG_BLCKSZ];
+		size_t overlap = end - pagebegptr;
+		if (overlap <= len)
+			memcpy(page, data + len - overlap, overlap);
+		else
+			memcpy(page + overlap - len, data, len);
+	}
+	LWLockRelease(WALBufMappingLock);
+}

src/include/access/xlogrecovery.h

@@ -155,4 +155,6 @@ extern void RecoveryRequiresIntParameter(const char *param_name, int currValue,
 
 extern void xlog_outdesc(StringInfo buf, XLogReaderState *record);
 
+extern void XLogUpdateWalBuffers(char* data, XLogRecPtr start, size_t len);
+
 #endif							/* XLOGRECOVERY_H */