Jim Nasby wrote:
On Jun 17, 2007, at 4:39 AM, Simon Riggs wrote:
pg_start_backup() should be a normal checkpoint I think. No need for
backup to be an intrusive process.

Good point. A spread out checkpoint can take a long time to finish,
though. Is there risk for running into a timeout or something if it
takes say 10 minutes for a call to pg_start_backup to finish?

That would be annoying, but the alternative is for backups to seriously
effect performance, which would defeat the object of the HOT backup.
It's not like its immediate right now, so we'd probably be moving from
2-3 mins to 10 mins in your example. Most people are expecting their
backups to take a long time anyway, so thats OK.

We should document it, though; otherwise I can see a bunch of confused users wondering why pg_start_backup takes so long. Remember that with longer checkpoints, the odds of them calling pg_start_backup during one and having to wait are much greater.

If pg_start_backup initiates a non-immediate, smoothed checkpoint, how about a checkpoint that's in progress when pg_start_backup is called? Should that be hurried, so we can start the backup sooner? Probably not, which means we'll need yet another mode to RequestCheckpoint: request a non-immediate checkpoint, but if there's a checkpoint already running, don't rush it.

  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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