Fix typos in comments

The changes done in this commit impact comments with no direct
user-visible changes, with fixes for incorrect function, variable or
structure names.

Author: Alexander Lakhin
Discussion: https://postgr.es/m/e8c38840-596a-83d6-bd8d-cebc51111572@gmail.com

src/backend/access/gist/gistxlog.c

@@ -580,8 +580,8 @@ gistXLogAssignLSN(void)
 	int			dummy = 0;
 
 	/*
-	 * Records other than SWITCH_WAL must have content. We use an integer 0 to
-	 * follow the restriction.
+	 * Records other than XLOG_SWITCH must have content. We use an integer 0
+	 * to follow the restriction.
 	 */
 	XLogBeginInsert();
 	XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT);

src/backend/access/heap/heapam.c

@@ -1223,7 +1223,7 @@ heap_set_tidrange(TableScanDesc sscan, ItemPointer mintid,
 	 * Calculate the first block and the number of blocks we must scan. We
 	 * could be more aggressive here and perform some more validation to try
 	 * and further narrow the scope of blocks to scan by checking if the
-	 * lowerItem has an offset above MaxOffsetNumber.  In this case, we could
+	 * lowestItem has an offset above MaxOffsetNumber.  In this case, we could
 	 * advance startBlk by one.  Likewise, if highestItem has an offset of 0
 	 * we could scan one fewer blocks.  However, such an optimization does not
 	 * seem worth troubling over, currently.

src/backend/access/heap/heapam_handler.c

@@ -816,7 +816,7 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
 				 * If the last pages of the scan were empty, we would go to
 				 * the next phase while heap_blks_scanned != heap_blks_total.
 				 * Instead, to ensure that heap_blks_scanned is equivalent to
-				 * total_heap_blks after the table scan phase, this parameter
+				 * heap_blks_total after the table scan phase, this parameter
 				 * is manually updated to the correct value when the table
 				 * scan finishes.
 				 */

src/backend/access/heap/pruneheap.c

@@ -198,8 +198,7 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
 		/*
 		 * Now that we have buffer lock, get accurate information about the
 		 * page's free space, and recheck the heuristic about whether to
-		 * prune. (We needn't recheck PageIsPrunable, since no one else could
-		 * have pruned while we hold pin.)
+		 * prune.
 		 */
 		if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
 		{
@@ -490,7 +489,7 @@ heap_page_prune(Relation relation, Buffer buffer,
  *
  * Due to its cost we also only want to call
  * TransactionIdLimitedForOldSnapshots() if necessary, i.e. we might not have
- * done so in heap_hot_prune_opt() if pd_prune_xid was old enough. But we
+ * done so in heap_page_prune_opt() if pd_prune_xid was old enough. But we
  * still want to be able to remove rows that are too new to be removed
  * according to prstate->vistest, but that can be removed based on
  * old_snapshot_threshold. So we call TransactionIdLimitedForOldSnapshots() on

src/backend/access/heap/vacuumlazy.c

@@ -2575,7 +2575,7 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
 	END_CRIT_SECTION();
 
 	/*
-	 * Now that we have removed the LD_DEAD items from the page, once again
+	 * Now that we have removed the LP_DEAD items from the page, once again
 	 * check if the page has become all-visible.  The page is already marked
 	 * dirty, exclusively locked, and, if needed, a full page image has been
 	 * emitted.

src/backend/access/nbtree/nbtsplitloc.c

@@ -119,7 +119,7 @@ static inline IndexTuple _bt_split_firstright(FindSplitData *state,
  * righthand page (which is called firstrightoff), plus a boolean
  * indicating whether the new tuple goes on the left or right page.  You
  * can think of the returned state as a point _between_ two adjacent data
- * items (laftleft and firstright data items) on an imaginary version of
+ * items (lastleft and firstright data items) on an imaginary version of
  * origpage that already includes newitem.  The bool is necessary to
  * disambiguate the case where firstrightoff == newitemoff (i.e. it is
  * sometimes needed to determine if the firstright tuple for the split is

src/backend/access/transam/slru.c

@@ -809,7 +809,7 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruWriteAll fdata)
 	}
 
 	/*
-	 * During a WriteAll, we may already have the desired file open.
+	 * During a SimpleLruWriteAll, we may already have the desired file open.
 	 */
 	if (fdata)
 	{
@@ -864,7 +864,7 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruWriteAll fdata)
 			else
 			{
 				/*
-				 * In the unlikely event that we exceed MAX_FLUSH_BUFFERS,
+				 * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
 				 * fall back to treating it as a standalone write.
 				 */
 				fdata = NULL;
@@ -1478,7 +1478,7 @@ SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset)
  *
  * This assumes every uint32 >= FirstNormalTransactionId is a valid key.  It
  * assumes each value occupies a contiguous, fixed-size region of SLRU bytes.
- * (MultiXactMemberCtl separates flags from XIDs.  AsyncCtl has
+ * (MultiXactMemberCtl separates flags from XIDs.  NotifyCtl has
  * variable-length entries, no keys, and no random access.  These unit tests
  * do not apply to them.)
  */

src/backend/access/transam/xlogreader.c

@@ -1476,7 +1476,7 @@ err:
 }
 
 /*
- * Helper function to ease writing of XLogRoutine->page_read callbacks.
+ * Helper function to ease writing of XLogReaderRoutine->page_read callbacks.
  * If this function is used, caller must supply a segment_open callback in
  * 'state', as that is used here.
  *
@@ -1513,7 +1513,7 @@ WALRead(XLogReaderState *state,
 		/*
 		 * If the data we want is not in a segment we have open, close what we
 		 * have (if anything) and open the next one, using the caller's
-		 * provided openSegment callback.
+		 * provided segment_open callback.
 		 */
 		if (state->seg.ws_file < 0 ||
 			!XLByteInSeg(recptr, state->seg.ws_segno, state->segcxt.ws_segsize) ||