Horton

Re: Summary and Plan for Hot Standby

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndQuadrant.com>
To: Magnus Hagander <magnus@hagander.net>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Date: 2009-11-15T09:43:52Z
Lists: pgsql-hackers 
On Sun, 2009-11-15 at 10:00 +0100, Magnus Hagander wrote:

> What does the time depend on?

We need to wait for all current transactions to complete. (i.e. any
backend that has (or could) take an xid or an AccessExclusiveLock before
it commits.). Similar-ish to the wait for a CREATE INDEX CONCURRENTLY.

The standby already performs this wait in the case where we overflow the
snapshot, so we have >64 subtransactions on *any* current transaction on
the master. The reason for that is (again) performance on master: we
choose not to WAL log new subtransactions.

There are various ways around this and I'm certain we'll come up with
something ingenious but my main point is that we don't need to wait for
this issue to be solved in order for HS to be usable.

-- 
 Simon Riggs           www.2ndQuadrant.com