Remember last written LSN when it is first requested (#410)

* Remember last written LSN when it is first requested

* Return updated LSN in SetLastWrittenLSN

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>

Author: 2 people

src/backend/access/transam/xlog.c

@@ -6281,6 +6281,11 @@ GetLastWrittenLSN(RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno
 		entry = hash_search(lastWrittenLsnCache, &key, HASH_FIND, NULL);
 		if (entry != NULL)
 			lsn = entry->lsn;
+		else
+		{
+			LWLockRelease(LastWrittenLsnLock);
+			return SetLastWrittenLSNForBlock(lsn, rlocator, forknum, blkno);
+		}
 	}
 	else
 	{
@@ -6308,17 +6313,19 @@ GetLastWrittenLSN(RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno
  * rlocator.relNumber can be InvalidOid, in this case maxLastWrittenLsn is updated.
  * SetLastWrittenLsn with dummy rlocator is used by createdb and dbase_redo functions.
  */
-void
+XLogRecPtr
 SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks)
 {
 	if (lsn == InvalidXLogRecPtr || n_blocks == 0 || lastWrittenLsnCacheSize == 0)
-		return;
+		return lsn;
 
 	LWLockAcquire(LastWrittenLsnLock, LW_EXCLUSIVE);
 	if (rlocator.relNumber == InvalidOid)
 	{
 		if (lsn > XLogCtl->maxLastWrittenLsn)
 			XLogCtl->maxLastWrittenLsn = lsn;
+		else
+			lsn = XLogCtl->maxLastWrittenLsn;
 	}
 	else
 	{
@@ -6339,6 +6346,8 @@ SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumb
 			{
 				if (lsn > entry->lsn)
 					entry->lsn = lsn;
+				else
+					lsn = entry->lsn;
 				/* Unlink from LRU list */
 				dlist_delete(&entry->lru_node);
 			}
@@ -6361,34 +6370,35 @@ SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumb
 		}
 	}
 	LWLockRelease(LastWrittenLsnLock);
+	return lsn;
 }
 
 /*
  * SetLastWrittenLSNForBlock -- Set maximal LSN for block
  */
-void
+XLogRecPtr
 SetLastWrittenLSNForBlock(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum, BlockNumber blkno)
 {
-	SetLastWrittenLSNForBlockRange(lsn, rlocator, forknum, blkno, 1);
+	return SetLastWrittenLSNForBlockRange(lsn, rlocator, forknum, blkno, 1);
 }
 
 /*
  * SetLastWrittenLSNForRelation -- Set maximal LSN for relation metadata
  */
-void
+XLogRecPtr
 SetLastWrittenLSNForRelation(XLogRecPtr lsn, RelFileLocator rlocator, ForkNumber forknum)
 {
-	SetLastWrittenLSNForBlock(lsn, rlocator, forknum, REL_METADATA_PSEUDO_BLOCKNO);
+	return SetLastWrittenLSNForBlock(lsn, rlocator, forknum, REL_METADATA_PSEUDO_BLOCKNO);
 }
 
 /*
  * SetLastWrittenLSNForDatabase -- Set maximal LSN for the whole database
  */
-void
+XLogRecPtr
 SetLastWrittenLSNForDatabase(XLogRecPtr lsn)
 {
 	RelFileLocator dummyNode = {InvalidOid, InvalidOid, InvalidOid};
-	SetLastWrittenLSNForBlock(lsn, dummyNode, MAIN_FORKNUM, 0);
+	return SetLastWrittenLSNForBlock(lsn, dummyNode, MAIN_FORKNUM, 0);
 }
 
 void

src/include/access/xlog.h

@@ -261,10 +261,10 @@ extern XLogRecPtr GetLastImportantRecPtr(void);
 
 /* neon specifics */
 
-extern void SetLastWrittenLSNForBlock(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum, BlockNumber blkno);
-extern void SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks);
-extern void SetLastWrittenLSNForDatabase(XLogRecPtr lsn);
-extern void SetLastWrittenLSNForRelation(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum);
+extern XLogRecPtr SetLastWrittenLSNForBlock(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum, BlockNumber blkno);
+extern XLogRecPtr SetLastWrittenLSNForBlockRange(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum, BlockNumber from, BlockNumber n_blocks);
+extern XLogRecPtr SetLastWrittenLSNForDatabase(XLogRecPtr lsn);
+extern XLogRecPtr SetLastWrittenLSNForRelation(XLogRecPtr lsn, RelFileLocator relfilenode, ForkNumber forknum);
 extern XLogRecPtr GetLastWrittenLSN(RelFileLocator relfilenode, ForkNumber forknum, BlockNumber blkno);
 
 extern void SetRedoStartLsn(XLogRecPtr RedoStartLSN);