Re: Transaction Snapshots and Hot Standby

Le jeudi 11 septembre 2008, Heikki Linnakangas a écrit :
> Well, yes, but you can fall behind indefinitely that way. Imagine that
> each transaction on the slave lasts, say 10 minutes, with a new
> transaction starting every 5 minutes. On the master, there's a table
> that's being vacuumed (or HOT-updated) frequently, say after each
> transaction for simplicity. What can happen is that every transaction
> that finishes on the slave will only let the WAL replay advance by one
> XID before blocking on the snapshot of the next slave transaction. The
> WAL replay will advance at a rate of 0.2 TPM, while the master is
> generating 1.0 TPM.

What would forbid the slave to choose to replay all currently lagging WALs
each time it's given the choice to advance a little?
--
dim