> On 29 Oct 2015, at 14:39, Vladimir Borodin <r...@simply.name> wrote:
> f I understand right, with hot_standby_feedback = on standby tells the master 
> xmin of the earliest transaction on standby. And autovacuum worker on master 
> takes it into account when doing vacuum cleanup (because it can see it from 
> pg_replications_slots view), AFAIK with GetOldestXmin function. But I don’t 
> understand why with READ COMMITED transactions xmin in pg_replication_slots 
> view on master continues to increase while with REPEATABLE READ xmin freezes 
> until this transaction finishes.

Could it be a consequence of how REPEATABLE READ transactions handle snapshots? 
With REPEATABLE READ the snapshot is acquired only once at the beginning of a 
transaction; a READ COMMITTED transaction re-evaluates its snapshot with each 
new command.


Kind regards,

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