From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 2 Jun 2011 17:28:52 +0000 (-0400)
Subject: Avoid creating init fork for unlogged indexes when it already exists.
X-Git-Tag: REL9_1_BETA2~42
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b8be5431a2baa2ea4a5140f1a49c3360deb4d64e;p=postgresql

Avoid creating init fork for unlogged indexes when it already exists.

Report by Greg Sabino Mullane, diagnosis and preliminary patch by
Andres Freund, corrections by me.
---

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index a0898e0048..53b4c3c59b 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1741,9 +1741,14 @@ index_build(Relation heapRelation,
 	Assert(PointerIsValid(stats));
 
 	/*
-	 * If this is an unlogged index, we need to write out an init fork for it.
-	 */
-	if (heapRelation->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
+	 * If this is an unlogged index, we may need to write out an init fork for
+	 * it -- but we must first check whether one already exists.  If, for
+	 * example, an unlogged relation is truncated in the transaction that
+	 * created it, or truncated twice in a subsequent transaction, the
+	 * relfilenode won't change, and nothing needs to be done here.
+	 */
+	if (heapRelation->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED
+	    && !smgrexists(indexRelation->rd_smgr, INIT_FORKNUM))
 	{
 		RegProcedure ambuildempty = indexRelation->rd_am->ambuildempty;