amcheck: Skip unlogged relations during recovery.

contrib/amcheck failed to consider the possibility that unlogged
relations will not have any main relation fork files when running in hot
standby mode.  This led to low-level "can't happen" errors that complain
about the absence of a relfilenode file.

To fix, simply skip verification of unlogged index relations during
recovery.  In passing, add a direct check for the presence of a main
fork just before verification proper begins, so that we cleanly verify
the presence of the main relation fork file.

Author: Andrey Borodin, Peter Geoghegan
Reported-By: Andrey Borodin
Diagnosed-By: Andrey Borodin
Discussion: https://postgr.es/m/DA9B33AC-53CB-4643-96D4-7A0BBC037FA1@yandex-team.ru
Backpatch: 10-, where amcheck was introduced.

diff --git a/contrib/amcheck/verify_nbtree.c b/contrib/amcheck/verify_nbtree.c
index afbcd8ce7683b40aed958d01df0c4514b1816c13..f88d06997f77c0950d1691d69f3befa7c048b31b 100644 (file)
--- a/contrib/amcheck/verify_nbtree.c
+++ b/contrib/amcheck/verify_nbtree.c
@@ -33,6 +33,7 @@
 #include "lib/bloomfilter.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
+#include "storage/smgr.h"
 #include "utils/memutils.h"
 #include "utils/snapmgr.h"
 
@@ -120,6 +121,7 @@ PG_FUNCTION_INFO_V1(bt_index_parent_check);
 static void bt_index_check_internal(Oid indrelid, bool parentcheck,
                                                bool heapallindexed);
 static inline void btree_index_checkable(Relation rel);
+static inline bool btree_index_mainfork_expected(Relation rel);
 static void bt_check_every_level(Relation rel, Relation heaprel,
                                         bool readonly, bool heapallindexed);
 static BtreeLevel bt_check_level_from_leftmost(BtreeCheckState *state,
@@ -252,8 +254,18 @@ bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed)
        /* Relation suitable for checking as B-Tree? */
        btree_index_checkable(indrel);
 
-       /* Check index, possibly against table it is an index on */
-       bt_check_every_level(indrel, heaprel, parentcheck, heapallindexed);
+       if (btree_index_mainfork_expected(indrel))
+       {
+               RelationOpenSmgr(indrel);
+               if (!smgrexists(indrel->rd_smgr, MAIN_FORKNUM))
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_INDEX_CORRUPTED),
+                                        errmsg("index \"%s\" lacks a main relation fork",
+                                                       RelationGetRelationName(indrel))));
+
+               /* Check index, possibly against table it is an index on */
+               bt_check_every_level(indrel, heaprel, parentcheck, heapallindexed);
+       }
 
        /*
         * Release locks early. That's ok here because nothing in the called
@@ -299,6 +311,28 @@ btree_index_checkable(Relation rel)
                                 errdetail("Index is not valid")));
 }
 
+/*
+ * Check if B-Tree index relation should have a file for its main relation
+ * fork.  Verification uses this to skip unlogged indexes when in hot standby
+ * mode, where there is simply nothing to verify.
+ *
+ * NB: Caller should call btree_index_checkable() before calling here.
+ */
+static inline bool
+btree_index_mainfork_expected(Relation rel)
+{
+       if (rel->rd_rel->relpersistence != RELPERSISTENCE_UNLOGGED ||
+               !RecoveryInProgress())
+               return true;
+
+       ereport(NOTICE,
+                       (errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
+                        errmsg("cannot verify unlogged index \"%s\" during recovery, skipping",
+                                       RelationGetRelationName(rel))));
+
+       return false;
+}
+
 /*
  * Main entry point for B-Tree SQL-callable functions. Walks the B-Tree in
  * logical order, verifying invariants as it goes.  Optionally, verification