mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Remove inadequate assertion check in CTE inlining.

Browse Source 
inline_cte() expected to find exactly as many references to the
target CTE as its cterefcount indicates.  While that should be
accurate for the tree as emitted by the parser, there are some
optimizations that occur upstream of here that could falsify it,
notably removal of unused subquery output expressions.

Trying to make the accounting 100% accurate seems expensive and
doomed to future breakage.  It's not really worth it, because
all this code is protecting is downstream assumptions that every
referenced CTE has a plan.  Let's convert those assertions to
regular test-and-elog just in case there's some actual problem,
and then drop the failing assertion.

Per report from Tomas Vondra (thanks also to Richard Guo for
analysis).  Back-patch to v12 where the faulty code came in.

Discussion: https://postgr.es/m/29196a1e-ed47-c7ca-9be2-b1c636816183@enterprisedb.com
This commit is contained in:
Tom Lane 2022-04-21 17:58:52 -04:00
parent 1c60a99dd9
commit e6440d5007
6 changed files with 101 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
src/backend/optimizer/path/allpaths.c
View File

@ -2538,7 +2538,8 @@ set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
if (ndx >= list_length(cteroot->cte_plan_ids))
elog(ERROR, "could not find plan for CTE \"%s\"", rte->ctename);
plan_id = list_nth_int(cteroot->cte_plan_ids, ndx);
Assert(plan_id > 0);
if (plan_id <= 0)
elog(ERROR, "no plan was made for CTE \"%s\"", rte->ctename);
cteplan = (Plan *) list_nth(root->glob->subplans, plan_id - 1);
/* Mark rel with estimated output rows, width, etc */

3
src/backend/optimizer/plan/createplan.c
View File

@ -3709,7 +3709,8 @@ create_ctescan_plan(PlannerInfo *root, Path *best_path,
if (ndx >= list_length(cteroot->cte_plan_ids))
elog(ERROR, "could not find plan for CTE \"%s\"", rte->ctename);
plan_id = list_nth_int(cteroot->cte_plan_ids, ndx);
Assert(plan_id > 0);
if (plan_id <= 0)
elog(ERROR, "no plan was made for CTE \"%s\"", rte->ctename);
foreach(lc, cteroot->init_plans)
{
ctesplan = (SubPlan *) lfirst(lc);

8
src/backend/optimizer/plan/subselect.c
View File

@ -64,7 +64,6 @@ typedef struct inline_cte_walker_context
{
const char *ctename; /* name and relative level of target CTE */
int levelsup;
int refcount; /* number of remaining references */
Query *ctequery; /* query to substitute */
} inline_cte_walker_context;
@ -1131,13 +1130,9 @@ inline_cte(PlannerInfo *root, CommonTableExpr *cte)
context.ctename = cte->ctename;
/* Start at levelsup = -1 because we'll immediately increment it */
context.levelsup = -1;
context.refcount = cte->cterefcount;
context.ctequery = castNode(Query, cte->ctequery);
(void) inline_cte_walker((Node *) root->parse, &context);
/* Assert we replaced all references */
Assert(context.refcount == 0);
}
static bool
@ -1200,9 +1195,6 @@ inline_cte_walker(Node *node, inline_cte_walker_context *context)
rte->coltypes = NIL;
rte->coltypmods = NIL;
rte->colcollations = NIL;
/* Count the number of replacements we've done */
context->refcount--;
}
return false;

3
src/include/nodes/pathnodes.h
View File

@ -258,7 +258,8 @@ struct PlannerInfo
List *init_plans; /* init SubPlans for query */
List *cte_plan_ids; /* per-CTE-item list of subplan IDs */
List *cte_plan_ids; /* per-CTE-item list of subplan IDs (or -1 if
* no subplan was made for that CTE) */
List *multiexpr_params; /* List of Lists of Params for MULTIEXPR
* subquery outputs */

64
src/test/regress/expected/with.out
View File

@ -1766,6 +1766,70 @@ SELECT * FROM bug6051_3;
---
(0 rows)
-- check case where CTE reference is removed due to optimization
EXPLAIN (VERBOSE, COSTS OFF)
SELECT q1 FROM
(
WITH t_cte AS (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
QUERY PLAN
--------------------------------------
Subquery Scan on ss
Output: ss.q1
-> Seq Scan on public.int8_tbl i8
Output: i8.q1, NULL::bigint
(4 rows)
SELECT q1 FROM
(
WITH t_cte AS (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
q1
------------------
123
123
4567890123456789
4567890123456789
4567890123456789
(5 rows)
EXPLAIN (VERBOSE, COSTS OFF)
SELECT q1 FROM
(
WITH t_cte AS MATERIALIZED (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
QUERY PLAN
---------------------------------------------
Subquery Scan on ss
Output: ss.q1
-> Seq Scan on public.int8_tbl i8
Output: i8.q1, NULL::bigint
CTE t_cte
-> Seq Scan on public.int8_tbl t
Output: t.q1, t.q2
(7 rows)
SELECT q1 FROM
(
WITH t_cte AS MATERIALIZED (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
q1
------------------
123
123
4567890123456789
4567890123456789
4567890123456789
(5 rows)
-- a truly recursive CTE in the same list
WITH RECURSIVE t(a) AS (
SELECT 0

31
src/test/regress/sql/with.sql
View File

@ -842,6 +842,37 @@ COMMIT;
SELECT * FROM bug6051_3;
-- check case where CTE reference is removed due to optimization
EXPLAIN (VERBOSE, COSTS OFF)
SELECT q1 FROM
(
WITH t_cte AS (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
SELECT q1 FROM
(
WITH t_cte AS (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
EXPLAIN (VERBOSE, COSTS OFF)
SELECT q1 FROM
(
WITH t_cte AS MATERIALIZED (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
SELECT q1 FROM
(
WITH t_cte AS MATERIALIZED (SELECT * FROM int8_tbl t)
SELECT q1, (SELECT q2 FROM t_cte WHERE t_cte.q1 = i8.q1) AS t_sub
FROM int8_tbl i8
) ss;
-- a truly recursive CTE in the same list
WITH RECURSIVE t(a) AS (
SELECT 0