possible bug

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От	Les
Тема	possible bug
Дата	21 октября 2022 г. 20:50:39
Msg-id	CAKXe9UBmUy-GGb8h91CXe+KKfcTmW0k=F0_5k5AAz0Psdg85eg@mail.gmail.com обсуждение исходный текст
Ответы	Re: possible bug (Adrian Klaver <adrian.klaver@aklaver.com>) Re: possible bug (Les <nagylzs@gmail.com>) Re: possible bug (Tom Lane <tgl@sss.pgh.pa.us>)
Список	pgsql-general

Дерево обсуждения

Hello,

We had a support request today, and we have narrowed down the problem to a query that behaves very strangely. The actual query was much more complicated, but I came up with this minimal example.

This is what we have seen inside our application:

select * from test where id in (26643094740, 26437091668);

id |code|regno|col_3|
-----------+----+-----+-----+
26437091668|TA-T| 2632| 1|

26643094740|PEG | 2905| 1|

select * from test where id = 26643094740;

id |code|regno|col_3|
-----------+----+-----+-----+

26643094740|PEG | 2905| 0|

The problem: value of col_3 changes for id=26643094740 if I query two rows vs. one row. This is without changing any data. The problem is 100% repeatable, if I query two rows from the same view, then I get different data for one of the rows.

I suspect that this is a bug. But I might be wrong. Please help me!

The actual test view looks like this:

create view test as
SELECT
c.id,
tt.code,
c.regno,
(
select count(*)
FROM kap.course_user cu
JOIN wf.workflow w_1 ON w_1.rec_id = cu.id AND w_1.head_table_id = 25408438504
where cu.is_active AND cu.course_id = c.id AND w_1.station_id = 25406740434
) AS col_3
FROM
kap.course c
INNER JOIN kap.training_type tt ON tt.id = c.training_type_id;

Below are some DDL s (simplified, the actual tables contain much more fields).

Do you think that this might be a bug? If not, then can somebody please explain how this can happen?

Laszlo

explain analyze select * from test where id in (26643094740, 26437091668);

QUERY PLAN |
-------------------------------------------------------------------------------------------------------------------------------------------------------+
Hash Join (cost=16.08..124.99 rows=2 width=29) (actual time=0.067..0.107 rows=2 loops=1) |
Hash Cond: (tt.id = c.training_type_id) |
-> Seq Scan on training_type tt (cost=0.00..12.71 rows=71 width=13) (actual time=0.004..0.033 rows=71 loops=1) |
-> Hash (cost=16.05..16.05 rows=2 width=24) (actual time=0.024..0.025 rows=2 loops=1) |
Buckets: 1024 Batches: 1 Memory Usage: 9kB |
-> Bitmap Heap Scan on course c (cost=8.58..16.05 rows=2 width=24) (actual time=0.018..0.021 rows=2 loops=1) |
Recheck Cond: (id = ANY ('{26643094740,26437091668}'::bigint[])) |
Heap Blocks: exact=2 |
-> Bitmap Index Scan on pk_course (cost=0.00..8.58 rows=2 width=0) (actual time=0.012..0.012 rows=2 loops=1) |
Index Cond: (id = ANY ('{26643094740,26437091668}'::bigint[])) |
SubPlan 1 |
-> Aggregate (cost=47.91..47.92 rows=1 width=8) (actual time=0.014..0.014 rows=1 loops=2) |
-> Nested Loop (cost=0.59..47.90 rows=1 width=0) (actual time=0.010..0.012 rows=1 loops=2) |
-> Index Scan using workflow_idx_station on workflow w_1 (cost=0.29..22.90 rows=3 width=8) (actual time=0.005..0.007 rows=1 loops=2) |
Index Cond: (station_id = '25406740434'::bigint) |
Filter: (head_table_id = '25408438504'::bigint) |
-> Memoize (cost=0.30..8.32 rows=1 width=8) (actual time=0.004..0.004 rows=1 loops=2) |
Cache Key: w_1.rec_id |
Hits: 1 Misses: 1 Evictions: 0 Overflows: 0 Memory Usage: 1kB |
-> Index Scan using pk_course_user on course_user cu (cost=0.29..8.31 rows=1 width=8) (actual time=0.005..0.005 rows=1 loops=1)|
Index Cond: (id = w_1.rec_id) |
Filter: (is_active AND (course_id = c.id)) |
Planning Time: 0.527 ms |
Execution Time: 0.175 ms |

explain analyze select * from test where id in (26643094740)

QUERY PLAN |
-------------------------------------------------------------------------------------------------------------------------------------------------------+
Nested Loop (cost=0.42..64.60 rows=1 width=29) (actual time=0.033..0.035 rows=1 loops=1) |
-> Index Scan using pk_course on course c (cost=0.28..8.30 rows=1 width=24) (actual time=0.007..0.008 rows=1 loops=1) |
Index Cond: (id = '26643094740'::bigint) |
-> Index Scan using pk_training_type on training_type tt (cost=0.14..8.16 rows=1 width=13) (actual time=0.002..0.002 rows=1 loops=1) |
Index Cond: (id = c.training_type_id) |
SubPlan 1 |
-> Aggregate (cost=47.91..47.92 rows=1 width=8) (actual time=0.018..0.019 rows=1 loops=1) |
-> Nested Loop (cost=0.59..47.90 rows=1 width=0) (actual time=0.017..0.017 rows=0 loops=1) |
-> Index Scan using workflow_idx_station on workflow w_1 (cost=0.29..22.90 rows=3 width=8) (actual time=0.007..0.009 rows=1 loops=1) |
Index Cond: (station_id = '25406740434'::bigint) |
Filter: (head_table_id = '25408438504'::bigint) |
-> Memoize (cost=0.30..8.32 rows=1 width=8) (actual time=0.007..0.007 rows=0 loops=1) |
Cache Key: w_1.rec_id |
Hits: 0 Misses: 1 Evictions: 0 Overflows: 0 Memory Usage: 1kB |
-> Index Scan using pk_course_user on course_user cu (cost=0.29..8.31 rows=1 width=8) (actual time=0.005..0.005 rows=0 loops=1)|
Index Cond: (id = w_1.rec_id) |
Filter: (is_active AND (course_id = c.id)) |
Rows Removed by Filter: 1 |
Planning Time: 0.528 ms |
Execution Time: 0.096 ms |

CREATE TABLE kap.course (
id int8 NOT NULL,
training_type_id int8 NOT NULL,
regno int8 NOT NULL,

-- many more fields here...
CONSTRAINT pk_course PRIMARY KEY (id),
CONSTRAINT fk_course_training_type_id FOREIGN KEY (training_type_id) REFERENCES kap.training_type(id) DEFERRABLE

-- many more constraints here...
);

CREATE TABLE kap.training_type (
id int8 NOT NULL,
code text NOT NULL,
-- many more fields here

CONSTRAINT pk_training_type PRIMARY KEY (id)

-- many more constraints here
);
CREATE UNIQUE INDEX training_type_uidx_code ON kap.training_type USING btree (code);

CREATE TABLE kap.course_user (
id int8 NOT NULL,
is_active bool NOT NULL DEFAULT true,
course_id int8 NOT NULL,
sec_user_id int8 NOT NULL,
CONSTRAINT pk_course_user PRIMARY KEY (id),
CONSTRAINT fk_course_user_course_id FOREIGN KEY (course_id) REFERENCES kap.course(id) DEFERRABLE,
CONSTRAINT fk_course_user_sec_user_id FOREIGN KEY (sec_user_id) REFERENCES sys.sec_user(id) DEFERRABLE

-- many more constraints here...
);
CREATE UNIQUE INDEX course_user_uidx ON kap.course_user USING btree (course_id, sec_user_id);

CREATE TABLE wf.workflow (
id int8 NOT NULL,
wf_type_id int8 NOT NULL,
head_table_id int8 NOT NULL,
table_info_id int8 NOT NULL,
rec_id int8 NOT NULL,
station_id int8 NOT NULL,

-- many more fields here...
CONSTRAINT pk_workflow PRIMARY KEY (id),
CONSTRAINT fk_workflow_station_id FOREIGN KEY (station_id) REFERENCES wf.station(id) DEFERRABLE,
CONSTRAINT fk_workflow_table_info_id FOREIGN KEY (table_info_id) REFERENCES meta.table_info(id) DEFERRABLE,
CONSTRAINT fk_workflow_wf_type_id FOREIGN KEY (wf_type_id) REFERENCES wf.wf_type(id) DEFERRABLE

-- many more constraints here
);
CREATE UNIQUE INDEX uidx_ht ON wf.workflow USING btree (head_table_id, rec_id);
CREATE INDEX workflow_idx_station ON wf.workflow USING btree (station_id);
CREATE UNIQUE INDEX workflow_uidx_ht ON wf.workflow USING btree (head_table_id, rec_id);

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