3 files changed, 48 insertions, 6 deletions

diff --git a/src/backend/access/gist/gistbuild.c b/src/backend/access/gist/gistbuild.c
index b9c4e27e1a5..46d150f9d82 100644
--- a/src/backend/access/gist/gistbuild.c
+++ b/src/backend/access/gist/gistbuild.c
@@ -191,7 +191,7 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 		PageSetLSN(page, recptr);
 	}
 	else
-		PageSetLSN(page, gistGetFakeLSN(heap));
+		PageSetLSN(page, gistGetFakeLSN(index));
 
 	UnlockReleaseBuffer(buffer);
 
diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index 55cccd247a0..d17965aa4b8 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -972,23 +972,44 @@ gistproperty(Oid index_oid, int attno,
 }
 
 /*
- * Temporary and unlogged GiST indexes are not WAL-logged, but we need LSNs
- * to detect concurrent page splits anyway. This function provides a fake
- * sequence of LSNs for that purpose.
+ * Some indexes are not WAL-logged, but we need LSNs to detect concurrent page
+ * splits anyway. This function provides a fake sequence of LSNs for that
+ * purpose.
  */
 XLogRecPtr
 gistGetFakeLSN(Relation rel)
 {
-	static XLogRecPtr counter = 1;
-
 	if (rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP)
 	{
 		/*
 		 * Temporary relations are only accessible in our session, so a simple
 		 * backend-local counter will do.
 		 */
+		static XLogRecPtr counter = 1;
+
 		return counter++;
 	}
+	else if (rel->rd_rel->relpersistence == RELPERSISTENCE_PERMANENT)
+	{
+		/*
+		 * WAL-logging on this relation will start after commit, so its LSNs
+		 * must be distinct numbers smaller than the LSN at the next commit.
+		 * Emit a dummy WAL record if insert-LSN hasn't advanced after the
+		 * last call.
+		 */
+		static XLogRecPtr lastlsn = InvalidXLogRecPtr;
+		XLogRecPtr	currlsn = GetXLogInsertRecPtr();
+
+		/* Shouldn't be called for WAL-logging relations */
+		Assert(!RelationNeedsWAL(rel));
+
+		/* No need for an actual record if we already have a distinct LSN */
+		if (!XLogRecPtrIsInvalid(lastlsn) && lastlsn == currlsn)
+			currlsn = gistXLogAssignLSN();
+
+		lastlsn = currlsn;
+		return currlsn;
+	}
 	else
 	{
 		/*
diff --git a/src/backend/access/gist/gistxlog.c b/src/backend/access/gist/gistxlog.c
index 17e213967b9..93e64682131 100644
--- a/src/backend/access/gist/gistxlog.c
+++ b/src/backend/access/gist/gistxlog.c
@@ -505,6 +505,9 @@ gist_redo(XLogReaderState *record)
 		case XLOG_GIST_CREATE_INDEX:
 			gistRedoCreateIndex(record);
 			break;
+		case XLOG_GIST_ASSIGN_LSN:
+			/* nop. See gistGetFakeLSN(). */
+			break;
 		default:
 			elog(PANIC, "gist_redo: unknown op code %u", info);
 	}
@@ -624,6 +627,24 @@ gistXLogSplit(bool page_is_leaf,
 }
 
 /*
+ * Write an empty XLOG record to assign a distinct LSN.
+ */
+XLogRecPtr
+gistXLogAssignLSN(void)
+{
+	int			dummy = 0;
+
+	/*
+	 * Records other than SWITCH_WAL must have content. We use an integer 0 to
+	 * follow the restriction.
+	 */
+	XLogBeginInsert();
+	XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT);
+	XLogRegisterData((char *) &dummy, sizeof(dummy));
+	return XLogInsert(RM_GIST_ID, XLOG_GIST_ASSIGN_LSN);
+}
+
+/*
  * Write XLOG record describing a page update. The update can include any
  * number of deletions and/or insertions of tuples on a single index page.
  *