Store the deletion horizon XID for a deleted GIN page on the right page.

Commit b10714080 moved the GinPageSetDeleteXid() call to a spot where
the "page" variable was pointing to the wrong page, causing the XID
to be inserted on a page that's not being deleted, thus allowing later
GinPageIsRecyclable tests to recycle the deleted page too soon.

It might be a good idea to stop using the single "page" variable for
multiple purposes in this function.  But for the moment I just moved
the GinPageSetDeleteXid() call down beside the GinPageSetDeleted()
call, which seems like a more logical place for it anyway.

Back-patch to v11, as the faulty patch was.  (Fortunately, the bug
hasn't made it into any release yet.)

Discussion: https://postgr.es/m/21620.1581098806@sss.pgh.pa.us

diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index 260cedff88b429da2b8436c24e0e1eda63163b61..8ae4fd95a7bf7104eec1734bfedeac028cc29574 100644 (file)
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -165,9 +165,6 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
        page = BufferGetPage(lBuffer);
        GinPageGetOpaque(page)->rightlink = rightlink;
 
-       /* For deleted page remember last xid which could knew its address */
-       GinPageSetDeleteXid(page, ReadNewTransactionId());
-
        /* Delete downlink from parent */
        parentPage = BufferGetPage(pBuffer);
 #ifdef USE_ASSERT_CHECKING
@@ -186,7 +183,13 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
         * we shouldn't change rightlink field to save workability of running
         * search scan
         */
+
+       /*
+        * Mark page as deleted, and remember last xid which could know its
+        * address.
+        */
        GinPageSetDeleted(page);
+       GinPageSetDeleteXid(page, ReadNewTransactionId());
 
        MarkBufferDirty(pBuffer);
        MarkBufferDirty(lBuffer);