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 55a3a4bbe0c2a0b967243bfd8038eb91d6d89a62..05e7d678ed4baeb73a265ecb49659fb897afe9e6 100644 (file)
--- a/contrib/amcheck/verify_nbtree.c
+++ b/contrib/amcheck/verify_nbtree.c
@@ -35,6 +35,7 @@
 #include "lib/bloomfilter.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
+#include "storage/smgr.h"
 #include "utils/memutils.h"
 #include "utils/snapmgr.h"
 
@@ -128,6 +129,7 @@ PG_FUNCTION_INFO_V1(bt_index_parent_check);
 static void bt_index_check_internal(Oid indrelid, bool parentcheck,
                                    bool heapallindexed, bool rootdescend);
 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 heapkeyspace, bool readonly, bool heapallindexed,
                                 bool rootdescend);
@@ -225,7 +227,6 @@ bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed,
    Oid         heapid;
    Relation    indrel;
    Relation    heaprel;
-   bool        heapkeyspace;
    LOCKMODE    lockmode;
 
    if (parentcheck)
@@ -275,10 +276,22 @@ 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 */
-   heapkeyspace = _bt_heapkeyspace(indrel);
-   bt_check_every_level(indrel, heaprel, heapkeyspace, parentcheck,
-                        heapallindexed, rootdescend);
+   if (btree_index_mainfork_expected(indrel))
+   {
+       bool    heapkeyspace;
+
+       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 */
+       heapkeyspace = _bt_heapkeyspace(indrel);
+       bt_check_every_level(indrel, heaprel, heapkeyspace, parentcheck,
+                            heapallindexed, rootdescend);
+   }
 
    /*
     * Release locks early. That's ok here because nothing in the called
@@ -324,6 +337,28 @@ 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