Re: Tid scan increments value of pg_stat_all_tables.seq_scan. (but not seq_tup_read)

On 2020/02/06 15:04, Kasahara Tatsuhito wrote:
> Hi,
>
> On Thu, Feb 6, 2020 at 11:48 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
>> I think it'd be good if we could guard against b) via an isolation
>> test. It's more painful to do that for a), due to the unreliability of
>> stats at the moment (we have some tests, but they take a long time).
> Thanks for your advise, and agreed.
>
> I added a new (but minimal) isolation test for the case of tid scan.
> (v12 and HEAD will be failed this test. v11 and HEAD with my patch
> will be passed)

Isn't this test scenario a bit overkill? We can simply test that
as follows, instead.

CREATE TABLE test_tidscan AS SELECT 1 AS id;
BEGIN ISOLATION LEVEL SERIALIZABLE;
SELECT * FROM test_tidscan WHERE ctid = '(0,1)';
SELECT locktype, mode FROM pg_locks WHERE pid = pg_backend_pid() AND mode = 'SIReadLock';
COMMIT;

In the expected file, the result of query looking at pg_locks
should be matched with the following.

locktype | mode
----------+------------
tuple | SIReadLock

BTW, in master branch, locktype in that query result is "relation"
because of the issue.

Regards,

--
Fujii Masao
NTT DATA CORPORATION
Advanced Platform Technology Group
Research and Development Headquarters