Re: txid_status returns NULL for recently commited transactions

Sorry, some auto formatting in recent email.

Again wtih fixed formatiing:

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
template1 289957661 4157344464
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

The strangest thing is ShmemVariableCache->oldestClogXid == 2207340131 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) == false

Could anyone help me with understanding of txid_status behaviour?

Thanks,
Michail.