Horton

Re: Hot Standby (v9d)

Gregory Stark <stark@enterprisedb.com>

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From: Gregory Stark <stark@enterprisedb.com>
To: Hannu Krosing <hannu@krosing.net>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>, jd@commandprompt.com, Simon Riggs <simon@2ndQuadrant.com>, Mark Kirkwood <markir@paradise.net.nz>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2009-02-03T13:50:28Z
Lists: pgsql-hackers 
Hannu Krosing <hannu@krosing.net> writes:

> Actually we came up with a solution to this - use filesystem level
> snapshots (like LVM2+XFS or ZFS), and redirect backends with
> long-running queries to use fs snapshot mounted to a different
> mountpoint.

Uhm, how do you determine which snapshot to direct the backend to? There could
have been several generations of tuples in that tid since your query started.
Do you take a snapshot every time there's a vacuum-snapshot conflict and
record which snapshot goes with that snapshot?

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Get trained by Bruce Momjian - ask me about EnterpriseDB's PostgreSQL training!