Re: found xmin from before relfrozenxid on pg_catalog.pg_authid

​Hi everyone,

I just got the same issue on 9.6.8:

2018-05-15 11:52:01 MSK 33558 @ from [vxid:317/92895305 txid:0] [] ERROR:
found xmin 2808837517 from before relfrozenxid 248712603
2018-05-15 11:52:01 MSK 33558 @ from [vxid:317/92895305 txid:0] []
CONTEXT: automatic vacuum of table "template0.pg_catalog.pg_authid"

Additional details:

1) bt_index_check - no errors on both indexes.

2) SELECT pg_truncate_visibility_map('pg_authid'::regclass); + vacuum
freeze - doesn't help.

3)Total 6 rows affected:
template1=# select oid, ctid, xmin, xmax, cmin, cmax from pg_authid where
xmin::text::bigint > (select relfrozenxid::text::bigint from pg_class where
relname='pg_authid');
oid | ctid | xmin | xmax | cmin | cmax
-----------+--------+------------+------+------+------
183671986 | (0,90) | 3039161773 | 0 | 0 | 0
183106699 | (1,48) | 2576823237 | 0 | 0 | 0
183921770 | (1,50) | 3265971811 | 0 | 0 | 0
183921914 | (1,52) | 3266122344 | 0 | 0 | 0
187988173 | (1,58) | 4258893789 | 0 | 0 | 0
182424977 | (1,62) | 2808837517 | 0 | 0 | 0
on total two pages.

4) template1=# select relfrozenxid from pg_catalog.pg_class where relname =
'pg_authid';
relfrozenxid
--------------
2548304492

5)Rows itself looks pretty valid and correspond to the actual database
users.
7)No database/server crash happened last few years, no disk errors/problems.

I feel it could be related with vacuum skip locked pages patch + freeze +
shared catalog combination, but cannot prove it yet.
​
Looking for possible course of action.
Probably simplest fix - drop and recreate these 6 affected users, but so
far I willing spent some time research into this issue.

--
Maxim Boguk
Senior Postgresql DBA
http://dataegret.com/ <http://www.postgresql-consulting.com/>

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когда я так делаю ещё раз?"