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Added/Updated tests\functional\transactions\test_read_consist_sttm_restart_on_merge_01.py: added 'ROWS nn' after 'ORDER BY ...' clause, otherwise engine can choose 'PLAN SORT' which leads to materialization of cursor resultset and, in turn, to increased statement restart count. See notes.

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pavel-zotov 2024-11-20 20:14:16 +03:00
parent cf374b406a
commit 890ebd9201
1 changed files with 11 additions and 1 deletions
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tests/functional/transactions/test_read_consist_sttm_restart_on_merge_01.py
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@ -142,6 +142,16 @@ NOTES:
[25.11.2023] pzotov
Writing code requires more care since 6.0.0.150: ISQL does not allow specifying duplicate delimiters without any statements between them (two semicolon, two carets etc).
Merge expression defined in 'SQL_TO_BE_RESTARTED' must NOT end with semicolon!
[20.11.2024] pzotov
::: ACHTUNG ::: ENGINE MUST NOT USE 'PLAN SORT' IN THE QUERY WHICH HAS TO BE RESTARTED IN THIS TEST!
Number of statement restarts CAN BE GREATER than expected! This occurs if a table (which is handled) has no appropriate index or if optimizer decides to use
external sort (e.g. 'PLAN SORT') instead of index navigation. This affects only FB 6.x and can be seen on snapshots since 14.11.2024, see:
https://github.com/FirebirdSQL/firebird/commit/26e64e9c08f635d55ac7a111469498b3f0c7fe81 ("Cost-based decision between ORDER and SORT plans (#8316)").
This result was explained by Vlad (letter 19.11.2024 09:59): external sort forces engine to materialize cursor resultset. In such state, in turn, cursor can not
see records which not fall to this cursor expression or did not exist when cursor started its job.
Because of that, SQL_TO_BE_RESTARTED expression was changed: 'ROWS 10' was added after 'ORDER BY' clause to make optimizer choose 'PLAN ORDER' every time.
Perhaps, this change is temporary solution.
"""
import subprocess
@ -226,7 +236,7 @@ def test_1(act: Action, fn_worker_sql: Path, fn_worker_log: Path, fn_worker_err:
SQL_TO_BE_RESTARTED = f"""
merge /* {SQL_TAG_THAT_WE_WAITING_FOR} */ into {target_obj} t
using (select * from {target_obj} order by id) s on s.id=t.id
using (select * from {target_obj} order by id ROWS 10) s on s.id=t.id
when matched then
update set t.id = -t.id, t.x = -s.x
when not matched then