Home > mailing lists

How to detect txid visibility on standby server? - Mailing list pgsql-general

From	Sergey Burladyan
Subject	How to detect txid visibility on standby server?
Date	July 30, 2014 19:45:40
Msg-id	CAJ2ymdhN3DVsvhhofA62qhwqBxRuXYOJhTquC4RO4GCd0AXVxQ@mail.gmail.com Whole thread Raw
List	pgsql-general

Hello!

Is it possible to detect what master transaction is visible on standby?

I try to use txid_current_snapshot() but it return wrong result on standby:

_master_:

create table tmp.txid_test(txid bigint, ss txid_snapshot)

begin;

insert into tmp.txid_test values (txid_current(), txid_current_snapshot());

select * from tmp.txid_test;

=> 9098493097 '9098489391:9098493097:9098489391,9098493002,9098493088'

_standby_:

select txid_visible_in_snapshot(9098493097, txid_current_snapshot());

=> t

select count(*) from tmp.txid_test;

=> 0

So, txid_visible_in_snapshot say what 9098493097 is visible, but realy it is not, it still not

commited on master and count on standby return 0 rows.

PS: And what does it exactly mean to get txid_current_snapshot() from standby?

Sergey Burladyan

From: Adrian Klaver
Date: 30 July 2014, 17:38:49
Subject: Re: pgbouncer not finding pidfile

From: Kevin Goess
Date: 30 July 2014, 20:51:21
Subject: free RAM not being used for page cache