Yes, you are right about sessions.
Here is the case from the server log:
"deadlock detected","Process 2588 waits for ShareLock on transaction
1939192; blocked by process 16399. Process 16399 waits for ShareLock on
transaction 1939195; blocked by process 2588.
Process 2588:
UPDATE T1
SET ...
FROM trans1_T_tmp
WHERE ...
Process 16399: WITH agg_tmp AS (SELECT ... FROM trans2_T1_tmp GROUP BY
...), upd AS (UPDATE T1 SET ... FROM agg_tmp s WHERE ... RETURNING ...)
INSERT INTO T1 (...) SELECT ... FROM agg_tmp s LEFT JOIN upd t ON (...)
WHERE ...;","See server log for query details.",,,"while updating tuple
(388225,15) in relation ""T1"""," UPDATE T1
SET ...
FROM trans1_T_tmp
WHERE ...
",,,""
or another one:
"deadlock detected","Process 71490 waits for ShareLock on transaction
2001693; blocked by process 71221. Process 71221 waits for ShareLock on
transaction 2001689; blocked by process 71490.
Process 71490: WITH agg_tmp AS (SELECT ... FROM trans2_T1_tmp GROUP BY
...), upd AS (UPDATE T1 SET ... FROM agg_tmp s WHERE ... RETURNING ...)
INSERT INTO T1 (...) SELECT ... FROM agg_tmp s LEFT JOIN upd t ON (...)
WHERE ...;
Process 71221: UPDATE T1
SET ...
FROM trans1_T_tmp
WHERE ...
","See server log for query details.",,,"while updating
tuple (93716,27) in relation ""T1""","WITH agg_tmp AS (SELECT ... FROM
trans2_T1_tmp GROUP BY ...), upd AS (UPDATE T1 SET ... FROM agg_tmp s
WHERE ... RETURNING ...) INSERT INTO T1 (...) SELECT ... FROM agg_tmp s
LEFT JOIN upd t ON (...) WHERE ...;
Process 71221: UPDATE T1
SET ...
FROM trans1_T_tmp
WHERE ...",,,""
On 07/02/16 11:14, Adrian Klaver wrote:
On 07/02/2016 09:54 AM, trafdev wrote:
> Hello.
>
> I have two transactions (trans1 and trans2) updating tables T1 and T2 in
> the same order, but in a different way.
>
> trans1 creates temp table, copies data from a file and updates tables T1
> and T2 from this temp table (using basic UPDATE form). It even commits
> changes in between T1 and T2 updates to reduce locks.
>
> trans2 creates two temp tables (T1_tmp and T2_tmp), copies data from
> files and updates T1 and T2 using [WITH ... AS ... RETURNING] approach.
> Unexciting rows should be inserted, existing updated (sum-ed with values
> from temp tables). Both T1 and T2 must be updated in the same
> transaction.
>
> There are no any FKs anywhere in these tables.
>
>
>
> trans1:
session1:
This is actually one session with multiple transactions, at least if I
am following correctly.
Assuming you have a:
BEGIN;
here.
>
> DROP TABLE IF EXISTS trans1_T_tmp;
>
> CREATE TABLE trans1_T_tmp (...);
>
> COMMIT
>
> COPY from FILE into trans1_T_tmp;
>
> BEGIN
> UPDATE T1
> SET ...
> FROM trans1_T_tmp
> WHERE ...
> COMMIT
>
> BEGIN
> UPDATE T2
> SET ...
> FROM (SELECT ... FROM trans1_T_tmp)
> WHERE ...
>
> DROP TABLE trans1_T_tmp;
> COMMIT
>
>
>
> trans2:
session2:
>
> BEGIN
>
> CREATE TABLE trans2_T1_tmp (...);
> COPY from FILE into trans2_T1_tmp;
> WITH agg_tmp AS (SELECT ... FROM trans2_T1_tmp GROUP BY ...), upd AS
> (UPDATE T1 SET ... FROM agg_tmp s WHERE ... RETURNING ...) INSERT INTO
> T1 (...) SELECT ... FROM agg_tmp s LEFT JOIN upd t ON (...) WHERE ...;
> DROP TABLE trans2_T1_tmp;
>
> CREATE TABLE trans2_T2_tmp (...);
> COPY from FILE into trans2_T2_tmp;
> WITH agg_tmp AS (SELECT ... FROM trans2_T2_tmp GROUP BY ...), upd AS
> (UPDATE T2 SET ... FROM agg_tmp s WHERE ... RETURNING ...) INSERT INTO
> T2 (...) SELECT ... FROM agg_tmp s LEFT JOIN upd t ON (...) WHERE ...;
> DROP TABLE trans2_T2_tmp;
>
> COMMIT
>
> By an unknown [for me] reason trans1 and trans2 often produce
> deadlocks...
What do the logs show as the error message?
>
> Could you explain what's the reason for that and how to avoid them?
> And is there exist a better replacement for WITH ... AS ... RETURNING ?
> Thanks!
>
>
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