Fix misbehavior with expression indexes on ON COMMIT DELETE ROWS tables.

We implement ON COMMIT DELETE ROWS by truncating tables marked that
way, which requires also truncating/rebuilding their indexes.  But
RelationTruncateIndexes asks the relcache for up-to-date copies of any
index expressions, which may cause execution of eval_const_expressions
on them, which can result in actual execution of subexpressions.
This is a bad thing to have happening during ON COMMIT.  Manuel Rigger
reported that use of a SQL function resulted in crashes due to
expectations that ActiveSnapshot would be set, which it isn't.
The most obvious fix perhaps would be to push a snapshot during
PreCommit_on_commit_actions, but I think that would just open the door
to more problems: CommitTransaction explicitly expects that no
user-defined code can be running at this point.

Fortunately, since we know that no tuples exist to be indexed, there
seems no need to use the real index expressions or predicates during
RelationTruncateIndexes.  We can set up dummy index expressions
instead (we do need something that will expose the right data type,
as there are places that build index tupdescs based on this), and
just ignore predicates and exclusion constraints.

In a green field it'd likely be better to reimplement ON COMMIT DELETE
ROWS using the same "init fork" infrastructure used for unlogged
relations.  That seems impractical without catalog changes though,
and even without that it'd be too big a change to back-patch.
So for now do it like this.

Per private report from Manuel Rigger.  This has been broken forever,
so back-patch to all supported branches.

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index f1600fe42f30995aa17aa8cd0e80b058f05ea38c..eea1638a2e6d3d0d5081978954522435968175a5 100644 (file)
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2740,8 +2740,15 @@ RelationTruncateIndexes(Relation heapRelation)
        /* Open the index relation; use exclusive lock, just to be sure */
        currentIndex = index_open(indexId, AccessExclusiveLock);
 
-       /* Fetch info needed for index_build */
-       indexInfo = BuildIndexInfo(currentIndex);
+       /*
+        * Fetch info needed for index_build.  Since we know there are no
+        * tuples that actually need indexing, we can use a dummy IndexInfo.
+        * This is slightly cheaper to build, but the real point is to avoid
+        * possibly running user-defined code in index expressions or
+        * predicates.  We might be getting invoked during ON COMMIT
+        * processing, and we don't want to run any such code then.
+        */
+       indexInfo = BuildDummyIndexInfo(currentIndex);
 
        /*
         * Now truncate the actual file (and discard buffers).

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index e4c832be1a9415b06729537ad195945994f3e8b8..535b29d4e70f97cd0a64979db1ff22b14cc4bab8 100644 (file)
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1689,6 +1689,65 @@ BuildIndexInfo(Relation index)
    return ii;
 }
 
+/* ----------------
+ *     BuildDummyIndexInfo
+ *         Construct a dummy IndexInfo record for an open index
+ *
+ * This differs from the real BuildIndexInfo in that it will never run any
+ * user-defined code that might exist in index expressions or predicates.
+ * Instead of the real index expressions, we return null constants that have
+ * the right types/typmods/collations.  Predicates and exclusion clauses are
+ * just ignored.  This is sufficient for the purpose of truncating an index,
+ * since we will not need to actually evaluate the expressions or predicates;
+ * the only thing that's likely to be done with the data is construction of
+ * a tupdesc describing the index's rowtype.
+ * ----------------
+ */
+IndexInfo *
+BuildDummyIndexInfo(Relation index)
+{
+   IndexInfo  *ii = makeNode(IndexInfo);
+   Form_pg_index indexStruct = index->rd_index;
+   int         i;
+   int         numKeys;
+
+   /* check the number of keys, and copy attr numbers into the IndexInfo */
+   numKeys = indexStruct->indnatts;
+   if (numKeys < 1 || numKeys > INDEX_MAX_KEYS)
+       elog(ERROR, "invalid indnatts %d for index %u",
+            numKeys, RelationGetRelid(index));
+   ii->ii_NumIndexAttrs = numKeys;
+   for (i = 0; i < numKeys; i++)
+       ii->ii_KeyAttrNumbers[i] = indexStruct->indkey.values[i];
+
+   /* fetch dummy expressions for expressional indexes */
+   ii->ii_Expressions = RelationGetDummyIndexExpressions(index);
+   ii->ii_ExpressionsState = NIL;
+
+   /* pretend there is no predicate */
+   ii->ii_Predicate = NIL;
+   ii->ii_PredicateState = NULL;
+
+   /* We ignore the exclusion constraint if any */
+   ii->ii_ExclusionOps = NULL;
+   ii->ii_ExclusionProcs = NULL;
+   ii->ii_ExclusionStrats = NULL;
+
+   /* other info */
+   ii->ii_Unique = indexStruct->indisunique;
+   ii->ii_ReadyForInserts = IndexIsReady(indexStruct);
+   /* assume not doing speculative insertion for now */
+   ii->ii_UniqueOps = NULL;
+   ii->ii_UniqueProcs = NULL;
+   ii->ii_UniqueStrats = NULL;
+
+   /* initialize index-build state to default */
+   ii->ii_Concurrent = false;
+   ii->ii_BrokenHotChain = false;
+
+   return ii;
+}
+
 /* ----------------
  *     BuildSpeculativeIndexInfo
  *         Add extra state to IndexInfo record

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 9aaf900d357258372b5408f63e60c612e8e981d7..07c938e0dacd844906f902d4f5452ad42bd7822f 100644 (file)
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -59,6 +59,7 @@
 #include "commands/policy.h"
 #include "commands/trigger.h"
 #include "miscadmin.h"
+#include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/prep.h"
@@ -4378,6 +4379,57 @@ RelationGetIndexExpressions(Relation relation)
    return result;
 }
 
+/*
+ * RelationGetDummyIndexExpressions -- get dummy expressions for an index
+ *
+ * Return a list of dummy expressions (just Const nodes) with the same
+ * types/typmods/collations as the index's real expressions.  This is
+ * useful in situations where we don't want to run any user-defined code.
+ */
+List *
+RelationGetDummyIndexExpressions(Relation relation)
+{
+   List       *result;
+   Datum       exprsDatum;
+   bool        isnull;
+   char       *exprsString;
+   List       *rawExprs;
+   ListCell   *lc;
+
+   /* Quick exit if there is nothing to do. */
+   if (relation->rd_indextuple == NULL ||
+       heap_attisnull(relation->rd_indextuple, Anum_pg_index_indexprs))
+       return NIL;
+
+   /* Extract raw node tree(s) from index tuple. */
+   exprsDatum = heap_getattr(relation->rd_indextuple,
+                             Anum_pg_index_indexprs,
+                             GetPgIndexDescriptor(),
+                             &isnull);
+   Assert(!isnull);
+   exprsString = TextDatumGetCString(exprsDatum);
+   rawExprs = (List *) stringToNode(exprsString);
+   pfree(exprsString);
+
+   /* Construct null Consts; the typlen and typbyval are arbitrary. */
+   result = NIL;
+   foreach(lc, rawExprs)
+   {
+       Node       *rawExpr = (Node *) lfirst(lc);
+
+       result = lappend(result,
+                        makeConst(exprType(rawExpr),
+                                  exprTypmod(rawExpr),
+                                  exprCollation(rawExpr),
+                                  1,
+                                  (Datum) 0,
+                                  true,
+                                  true));
+   }
+
+   return result;
+}
+
 /*
  * RelationGetIndexPredicate -- get the index predicate for an index
  *

diff --git a/src/include/catalog/index.h b/src/include/catalog/index.h
index 3fbebd066dcc8fff65099c889ead956333e0b87d..5941fec164ab3c105f7d034fc755eb05b0e9592f 100644 (file)
--- a/src/include/catalog/index.h
+++ b/src/include/catalog/index.h
@@ -82,6 +82,8 @@ extern void index_drop(Oid indexId, bool concurrent);
 
 extern IndexInfo *BuildIndexInfo(Relation index);
 
+extern IndexInfo *BuildDummyIndexInfo(Relation index);
+
 extern void BuildSpeculativeIndexInfo(Relation index, IndexInfo *ii);
 
 extern void FormIndexDatum(IndexInfo *indexInfo,

diff --git a/src/include/utils/relcache.h b/src/include/utils/relcache.h
index 6ea7dd2510a3a6f392fcab98563cad798524d446..8acc48b593a31dbed983ba9d8234ae240816fec8 100644 (file)
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -42,6 +42,7 @@ extern List *RelationGetIndexList(Relation relation);
 extern Oid RelationGetOidIndex(Relation relation);
 extern Oid RelationGetReplicaIndex(Relation relation);
 extern List *RelationGetIndexExpressions(Relation relation);
+extern List *RelationGetDummyIndexExpressions(Relation relation);
 extern List *RelationGetIndexPredicate(Relation relation);
 
 typedef enum IndexAttrBitmapKind

diff --git a/src/test/regress/expected/temp.out b/src/test/regress/expected/temp.out
index 0df7ba3ae1a3c0baa95d3d71254aaf2e9152a562..f491d6d30ed25df90cdb36360f96c5742db057fb 100644 (file)
--- a/src/test/regress/expected/temp.out
+++ b/src/test/regress/expected/temp.out
@@ -49,6 +49,8 @@ LINE 1: SELECT * FROM temptest;
                       ^
 -- Test ON COMMIT DELETE ROWS
 CREATE TEMP TABLE temptest(col int) ON COMMIT DELETE ROWS;
+-- while we're here, verify successful truncation of index with SQL function
+CREATE INDEX ON temptest(bit_length(''));
 BEGIN;
 INSERT INTO temptest VALUES (1);
 INSERT INTO temptest VALUES (2);

diff --git a/src/test/regress/sql/temp.sql b/src/test/regress/sql/temp.sql
index 6936b999295e8c6a928fcbf85cd9281788fe3283..b845bc05c7d360d99a011ca525b390d17df236df 100644 (file)
--- a/src/test/regress/sql/temp.sql
+++ b/src/test/regress/sql/temp.sql
@@ -55,6 +55,9 @@ SELECT * FROM temptest;
 
 CREATE TEMP TABLE temptest(col int) ON COMMIT DELETE ROWS;
 
+-- while we're here, verify successful truncation of index with SQL function
+CREATE INDEX ON temptest(bit_length(''));
+
 BEGIN;
 INSERT INTO temptest VALUES (1);
 INSERT INTO temptest VALUES (2);