From: | Michail Nikolaev <michail(dot)nikolaev(at)gmail(dot)com> |
---|---|
To: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, dsarafannikov(at)yandex(dot)ru |
Subject: | txid_status returns NULL for recently commited transactions |
Date: | 2018-09-25 16:47:40 |
Message-ID: | CANtu0ojcsB3c0g-7dzzh0vPiU77PAxRqtpQXm3P0dY5-3TKQ1A@mail.gmail.com |
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Lists: | pgsql-hackers |
Hello everyone.
I see strange beaviour of txid_status with one of my production servers.
SELECT txid_status(txid_current()) -> NULL
SELECT txid_current() -> 4447342811
It also returns null for recent commited and aborted transactions.
SELECT datname, age(datfrozenxid), datfrozenxid FROM pg_database;
template 0239961994 4207340131
postgres 289957756 4157344369 <(415)%20734-4369>
template1 289957661 4157344464 <(415)%20734-4464>
project 682347934 3764954191
GDB shows it happens because of TransactionIdPrecedes(xid,
ShmemVariableCache->oldestClogXid)) at txid.c:155.
xid_epoch = 1
xid = 150227913
now_epoch = 1
now_epoch_last_xid = 150468261
ShmemVariableCache->oldestClogXid = 2207340131 <(220)%20734-0131>
The strangest thing is ShmemVariableCache->oldestClogXid == 2207340131
<(220)%20734-0131> which is greater than current xid without an epoch
(150227913) .
Postgres was updated from 9.6 to PostgreSQL 10.4 (Ubuntu
10.4-2.pgdg14.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
4.8.4-2ubuntu1~14.04.4) 4.8.4, 64-bit.
Also, another small issue:
On the same database:
SELECT txid_status(BIGINT '4294967295') -> 'commited'.
SELECT txid_status(BIGINT '4294967296') -> NULL
Both tx ids are from my head and not valid.
First 'commited' happends because int32 overflow:
TransactionIdPrecedes(59856482, 2207340131 <(220)%20734-0131>) == false
Could anyone help me with understanding of txid_status behaviour?
Thanks,
Michail.
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