Fix SysCacheGetAttr() to handle the case where the specified syscache has not

been initialized yet.  This can happen because there are code paths that call
SysCacheGetAttr() on a tuple originally fetched from a different syscache
(hopefully on the same catalog) than the one specified in the call.  It
doesn't seem useful or robust to try to prevent that from happening, so just
improve the function to cope instead.  Per bug#2678 from Jeff Trout.  The
specific example shown by Jeff is new in 8.1, but to be on the safe side
I'm backpatching 8.0 as well.  We could patch 7.x similarly but I think
that's probably overkill, given the lack of evidence of old bugs of this ilk.

3 files changed, 24 insertions, 16 deletions

diff --git a/src/backend/utils/cache/catcache.c b/src/backend/utils/cache/catcache.c
index b6c210bc86..de6c522c61 100644
--- a/src/backend/utils/cache/catcache.c
+++ b/src/backend/utils/cache/catcache.c
@@ -976,7 +976,7 @@ CatalogCacheInitializeCache(CatCache *cache)
 		cache->cc_skey[i].sk_strategy = BTEqualStrategyNumber;
 		cache->cc_skey[i].sk_subtype = InvalidOid;
 
-		CACHE4_elog(DEBUG2, "CatalogCacheInit %s %d %p",
+		CACHE4_elog(DEBUG2, "CatalogCacheInitializeCache %s %d %p",
 					cache->cc_relname,
 					i,
 					cache);
@@ -991,18 +991,20 @@ CatalogCacheInitializeCache(CatCache *cache)
 /*
  * InitCatCachePhase2 -- external interface for CatalogCacheInitializeCache
  *
- * The only reason to call this routine is to ensure that the relcache
- * has created entries for all the catalogs and indexes referenced by
- * catcaches.  Therefore, open the index too.  An exception is the indexes
- * on pg_am, which we don't use (cf. IndexScanOK).
+ * One reason to call this routine is to ensure that the relcache has
+ * created entries for all the catalogs and indexes referenced by catcaches.
+ * Therefore, provide an option to open the index as well as fixing the
+ * cache itself.  An exception is the indexes on pg_am, which we don't use
+ * (cf. IndexScanOK).
  */
 void
-InitCatCachePhase2(CatCache *cache)
+InitCatCachePhase2(CatCache *cache, bool touch_index)
 {
 	if (cache->cc_tupdesc == NULL)
 		CatalogCacheInitializeCache(cache);
 
-	if (cache->id != AMOID &&
+	if (touch_index &&
+		cache->id != AMOID &&
 		cache->id != AMNAME)
 	{
 		Relation	idesc;
diff --git a/src/backend/utils/cache/syscache.c b/src/backend/utils/cache/syscache.c
index a0272f569b..b559e864bf 100644
--- a/src/backend/utils/cache/syscache.c
+++ b/src/backend/utils/cache/syscache.c
@@ -576,7 +576,7 @@ InitCatalogCachePhase2(void)
 	Assert(CacheInitialized);
 
 	for (cacheId = 0; cacheId < SysCacheSize; cacheId++)
-		InitCatCachePhase2(SysCache[cacheId]);
+		InitCatCachePhase2(SysCache[cacheId], true);
 }
 
 
@@ -773,6 +773,9 @@ SearchSysCacheExistsAttName(Oid relid, const char *attname)
  * As with heap_getattr(), if the attribute is of a pass-by-reference type
  * then a pointer into the tuple data area is returned --- the caller must
  * not modify or pfree the datum!
+ *
+ * Note: it is legal to use SysCacheGetAttr() with a cacheId referencing
+ * a different cache for the same catalog the tuple was fetched from.
  */
 Datum
 SysCacheGetAttr(int cacheId, HeapTuple tup,
@@ -781,15 +784,18 @@ SysCacheGetAttr(int cacheId, HeapTuple tup,
 {
 	/*
 	 * We just need to get the TupleDesc out of the cache entry, and then we
-	 * can apply heap_getattr().  We expect that the cache control data is
-	 * currently valid --- if the caller recently fetched the tuple, then it
-	 * should be.
+	 * can apply heap_getattr().  Normally the cache control data is already
+	 * valid (because the caller recently fetched the tuple via this same
+	 * cache), but there are cases where we have to initialize the cache here.
 	 */
-	if (cacheId < 0 || cacheId >= SysCacheSize)
+	if (cacheId < 0 || cacheId >= SysCacheSize ||
+		!PointerIsValid(SysCache[cacheId]))
 		elog(ERROR, "invalid cache id: %d", cacheId);
-	if (!PointerIsValid(SysCache[cacheId]) ||
-		!PointerIsValid(SysCache[cacheId]->cc_tupdesc))
-		elog(ERROR, "missing cache data for cache id %d", cacheId);
+	if (!PointerIsValid(SysCache[cacheId]->cc_tupdesc))
+	{
+		InitCatCachePhase2(SysCache[cacheId], false);
+		Assert(PointerIsValid(SysCache[cacheId]->cc_tupdesc));
+	}
 
 	return heap_getattr(tup, attributeNumber,
 						SysCache[cacheId]->cc_tupdesc,
diff --git a/src/include/utils/catcache.h b/src/include/utils/catcache.h
index 7d6f9ea3fb..bb9bbe2f22 100644
--- a/src/include/utils/catcache.h
+++ b/src/include/utils/catcache.h
@@ -166,7 +166,7 @@ extern CatCache *InitCatCache(int id, Oid reloid, Oid indexoid,
 			 int reloidattr,
 			 int nkeys, const int *key,
 			 int nbuckets);
-extern void InitCatCachePhase2(CatCache *cache);
+extern void InitCatCachePhase2(CatCache *cache, bool touch_index);
 
 extern HeapTuple SearchCatCache(CatCache *cache,
 			   Datum v1, Datum v2,