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 ac9df9eefe7d43112a32972205f86d4c19020b54..4d61e8e071cf09f3d9289e7e80b6e12f0edea97c 100644 (file)
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2795,8 +2795,15 @@ 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 a6b56d31007569ba64738c9f1613004e4efd900f..942d43db892ba8c06f84c9097c02856f95ea72c6 100644 (file)
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1706,6 +1706,69 @@ 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;
+
+       /* set up for possible use by index AM */
+       ii->ii_AmCache = NULL;
+       ii->ii_Context = CurrentMemoryContext;
+
+       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 24e830a39c19788984be0e11197b69f98c94a8a7..b67201846331d7161e0266a8c43b74531417c9ac 100644 (file)
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -65,6 +65,7 @@
 #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"
@@ -4816,6 +4817,57 @@ 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 ebca7740eae1f8bd9723dc1f8be5fa0d101062b2..7c56182c72311b97b8b374b8e6f95bfbdb0f89ed 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 3c53cefe4b4f440c68930c4875d190ac38692563..e2207ccd3d0a4aaf5c6513d2b33afcbfcb9742e5 100644 (file)
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -44,6 +44,7 @@ extern Oid    RelationGetOidIndex(Relation relation);
 extern Oid     RelationGetPrimaryKeyIndex(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 5e089ef050316b5daef5a9b064f96a33d6e0403c..47d58e829a389c6ae7953feda650e01c3a7b7843 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 f8d2a285c3c04c1c683ccb91b1ddb731a364c49b..e72618fa7f796fd26678b1a8f3e958559bf886e1 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);