Fix Assert failure in WITH RECURSIVE UNION queries

If the non-recursive part of a recursive CTE ended up using
TTSOpsBufferHeapTuple as the table slot type, then a duplicate value
could cause an Assert failure in CheckOpSlotCompatibility() when
checking the hash table for the duplicate value.  The expected slot type
for the deform step was TTSOpsMinimalTuple so the Assert failed when the
TTSOpsBufferHeapTuple slot was used.

This is a long-standing bug which we likely didn't notice because it
seems much more likely that the non-recursive term would have required
projection and used a TTSOpsVirtual slot, which CheckOpSlotCompatibility
is ok with.

There doesn't seem to be any harm done here other than the Assert
failure.  Both TTSOpsMinimalTuple and TTSOpsBufferHeapTuple slot types
require tuple deformation, so the EEOP_*_FETCHSOME ExprState step would
have properly existed in the ExprState.

The solution is to pass NULL for the ExecBuildGroupingEqual's 'lops'
parameter.  This means the ExprState's EEOP_*_FETCHSOME step won't
expect a fixed slot type.  This makes CheckOpSlotCompatibility() happy as
no checking is performed when the ExprEvalStep is not expecting a fixed
slot type.

Reported-by: Richard Guo
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/CAMbWs4-8U9q2LAtf8+ghV11zeUReA3AmrYkxzBEv0vKnDxwkKA@mail.gmail.com
Backpatch-through: 13, all supported versions

diff --git a/src/backend/executor/execGrouping.c b/src/backend/executor/execGrouping.c
index 0cc54a3449e3e118c361b5c76c357d240e66b0cd..5206240bc81ac950f888cfac1ed3c774d705210e 100644 (file)
--- a/src/backend/executor/execGrouping.c
+++ b/src/backend/executor/execGrouping.c
@@ -225,9 +225,8 @@ BuildTupleHashTableExt(PlanState *parent,
    allow_jit = metacxt != tablecxt;
 
    /* build comparator for all columns */
-   /* XXX: should we support non-minimal tuples for the inputslot? */
    hashtable->tab_eq_func = ExecBuildGroupingEqual(inputDesc, inputDesc,
-                                                   &TTSOpsMinimalTuple, &TTSOpsMinimalTuple,
+                                                   NULL, &TTSOpsMinimalTuple,
                                                    numCols,
                                                    keyColIdx, eqfuncoids, collations,
                                                    allow_jit ? parent : NULL);

diff --git a/src/test/regress/expected/with.out b/src/test/regress/expected/with.out
index 37178e70bef970fb9068bc0c2ea2d7983d1044ba..670d98784226a17791acabf9c9569c40d9f99a04 100644 (file)
--- a/src/test/regress/expected/with.out
+++ b/src/test/regress/expected/with.out
@@ -636,6 +636,21 @@ SELECT t1.id, t2.path, t2 FROM t AS t1 JOIN t AS t2 ON
  16 | {3,7,11,16} | (16,"{3,7,11,16}")
 (16 rows)
 
+CREATE TEMP TABLE duplicates (a INT NOT NULL);
+INSERT INTO duplicates VALUES(1), (1);
+-- Try out a recursive UNION case where the non-recursive part's table slot
+-- uses TTSOpsBufferHeapTuple and contains duplicate rows.
+WITH RECURSIVE cte (a) as (
+   SELECT a FROM duplicates
+   UNION
+   SELECT a FROM cte
+)
+SELECT a FROM cte;
+ a 
+---
+ 1
+(1 row)
+
 -- SEARCH clause
 create temp table graph0( f int, t int, label text );
 insert into graph0 values

diff --git a/src/test/regress/sql/with.sql b/src/test/regress/sql/with.sql
index 0f9c3956ac0be58df9cbc2ebc1b47990d3b1366a..befa3575a166669fa9799c2e439a1353c61a9b18 100644 (file)
--- a/src/test/regress/sql/with.sql
+++ b/src/test/regress/sql/with.sql
@@ -347,6 +347,18 @@ UNION ALL
 SELECT t1.id, t2.path, t2 FROM t AS t1 JOIN t AS t2 ON
 (t1.id=t2.id);
 
+CREATE TEMP TABLE duplicates (a INT NOT NULL);
+INSERT INTO duplicates VALUES(1), (1);
+
+-- Try out a recursive UNION case where the non-recursive part's table slot
+-- uses TTSOpsBufferHeapTuple and contains duplicate rows.
+WITH RECURSIVE cte (a) as (
+   SELECT a FROM duplicates
+   UNION
+   SELECT a FROM cte
+)
+SELECT a FROM cte;
+
 -- SEARCH clause
 
 create temp table graph0( f int, t int, label text );