Deduplicate PageIsNew() check in lazy_scan_heap().

The recheck isn't needed anymore, as RelationGetBufferForTuple() now
extends the relation with RBM_ZERO_AND_LOCK. Previously we needed to
handle the fact that relation extension extended the relation and then
separately acquired a lock on the page - while expecting that the page
is empty.

Reported-By: Ranier Vilela
Discussion: https://postgr.es/m/CAEudQArA_=J0D5T258xsCY6Xtf6wiH4b=QDPDgVS+WZUN10WDw@mail.gmail.com

Author: anarazel

src/backend/access/heap/vacuumlazy.c

@@ -1147,45 +1147,35 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 
 		if (PageIsNew(page))
 		{
-			bool		still_new;
-
 			/*
 			 * All-zeroes pages can be left over if either a backend extends
 			 * the relation by a single page, but crashes before the newly
 			 * initialized page has been written out, or when bulk-extending
 			 * the relation (which creates a number of empty pages at the tail
 			 * end of the relation, but enters them into the FSM).
 			 *
-			 * Make sure these pages are in the FSM, to ensure they can be
-			 * reused. Do that by testing if there's any space recorded for
-			 * the page. If not, enter it.
-			 *
 			 * Note we do not enter the page into the visibilitymap. That has
 			 * the downside that we repeatedly visit this page in subsequent
 			 * vacuums, but otherwise we'll never not discover the space on a
 			 * promoted standby. The harm of repeated checking ought to
 			 * normally not be too bad - the space usually should be used at
 			 * some point, otherwise there wouldn't be any regular vacuums.
+			 *
+			 * Make sure these pages are in the FSM, to ensure they can be
+			 * reused. Do that by testing if there's any space recorded for
+			 * the page. If not, enter it. We do so after releasing the lock
+			 * on the heap page, the FSM is approximate, after all.
 			 */
-
-			/*
-			 * Perform checking of FSM after releasing lock, the fsm is
-			 * approximate, after all.
-			 */
-			still_new = PageIsNew(page);
 			UnlockReleaseBuffer(buf);
 
-			if (still_new)
-			{
-				empty_pages++;
+			empty_pages++;
 
-				if (GetRecordedFreeSpace(onerel, blkno) == 0)
-				{
-					Size		freespace;
+			if (GetRecordedFreeSpace(onerel, blkno) == 0)
+			{
+				Size		freespace;
 
-					freespace = BufferGetPageSize(buf) - SizeOfPageHeaderData;
-					RecordPageWithFreeSpace(onerel, blkno, freespace);
-				}
+				freespace = BufferGetPageSize(buf) - SizeOfPageHeaderData;
+				RecordPageWithFreeSpace(onerel, blkno, freespace);
 			}
 			continue;
 		}