From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 11 Mar 2019 16:58:10 +0200
Subject: [PATCH 6/6] Misc cleanup.

---
 src/backend/access/gist/gistvacuum.c | 32 ++++++++++++++++------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/backend/access/gist/gistvacuum.c b/src/backend/access/gist/gistvacuum.c
index bf0b9d54f69..54a0adaf71f 100644
--- a/src/backend/access/gist/gistvacuum.c
+++ b/src/backend/access/gist/gistvacuum.c
@@ -419,7 +419,7 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 		Buffer		buffer;
 		Page		page;
 		OffsetNumber off,
-			maxoff;
+					maxoff;
 		IndexTuple  idxtuple;
 		ItemId	    iid;
 		OffsetNumber todelete[MaxOffsetNumber];
@@ -436,6 +436,8 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 		page = (Page) BufferGetPage(buffer);
 		if (PageIsNew(page) || GistPageIsDeleted(page) || GistPageIsLeaf(page))
 		{
+			/* HEIKKI: This page was an internal page earlier, but now it's something else.
+			 * Shouldn't happen... */
 			UnlockReleaseBuffer(buffer);
 			continue;
 		}
@@ -446,12 +448,13 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 			 off <= maxoff && ntodelete < maxoff-1;
 			 off = OffsetNumberNext(off))
 		{
+			BlockNumber leafBlockNo;
 			Buffer		leafBuffer;
 			Page		leafPage;
-			BlockNumber leafBlockNo;
 
 			iid = PageGetItemId(page, off);
 			idxtuple = (IndexTuple) PageGetItem(page, iid);
+
 			/* if this page was not empty in previous scan - we do not consider it */
 			leafBlockNo = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
 			if (!blockset_get(leafBlockNo, stats->emptyLeafPagesMap))
@@ -468,6 +471,7 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 			leafPage = (Page) BufferGetPage(leafBuffer);
 			if (!GistPageIsLeaf(leafPage))
 			{
+				/* it's not a leaf anymore? shouldn't happen.. */
 				UnlockReleaseBuffer(leafBuffer);
 				continue;
 			}
@@ -483,27 +487,29 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 				UnlockReleaseBuffer(leafBuffer);
 		}
 
-		/*
-		 * We will have to relock internal page in case of deletes:
-		 * we cannot lock child while holding parent lock without risk
-		 * of a deadlock
-		 */
-		LockBuffer(buffer, GIST_UNLOCK);
-
-		if (ntodelete)
+		if (ntodelete > 0)
 		{
 			TransactionId txid;
 			int			i;
 
+			/*
+			 * We will have to relock internal page in case of deletes:
+			 * we cannot lock child while holding parent lock without risk
+			 * of a deadlock
+			 */
+			LockBuffer(buffer, GIST_UNLOCK);
+
 			for (i = 0; i < ntodelete; i++)
 			{
 				Buffer	leafBuffer = buftodelete[i];
 				Page	leafPage;
+
+				/* FIXME: Aren't we still holding the lock from the loop above? */
 				LockBuffer(leafBuffer, GIST_EXCLUSIVE);
 				gistcheckpage(rel, leafBuffer);
 				leafPage = (Page) BufferGetPage(leafBuffer);
 				if (!GistPageIsLeaf(leafPage) /* not a leaf anymore */
-					|| PageGetMaxOffsetNumber(leafPage) != InvalidOffsetNumber /* Page is not empry */
+					|| PageGetMaxOffsetNumber(leafPage) != InvalidOffsetNumber /* Page is not empty */
 					|| (GistFollowRight(leafPage) || GistPageGetNSN(page) < GistPageGetNSN(leafPage)) /* No follow-right */
 					)
 				{
@@ -587,10 +593,8 @@ gistvacuum_recycle_pages(GistBulkDeleteResult *stats)
 				UnlockReleaseBuffer(buftodelete[i]);
 			}
 			END_CRIT_SECTION();
-
-			LockBuffer(buffer, GIST_UNLOCK);
 		}
 
-		ReleaseBuffer(buffer);
+		UnlockReleaseBuffer(buffer);
 	}
 }
-- 
2.20.1


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