| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Csaba Nagy <nagy(at)ecircle-ag(dot)com> |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Richard Huxton <dev(at)archonet(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Transaction Snapshots and Hot Standby |
| Date: | 2008-09-11 14:04:22 |
| Message-ID: | 48C92566.7060803@enterprisedb.com |
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| Lists: | pgsql-hackers |
Csaba Nagy wrote:
> and that means in fact that if you have
> continuously overlapping small transactions, the "blocking horizon"
> could be even blocked forever, as there'll always be a query running,
> and the new queries will always have the snapshot of the currently
> running ones because WAL recovery is stalled...
Hmm, no I don't think the WAL recovery can become completely stalled. To
completely stop progressing, we'd need to take a new snapshot that
includes transaction X, and at the same time be blocked on a vacuum
record that vacuums a tuple that's visible to transaction X. I don't
think that can happen, because for such a scenario to arise, in the
corresponding point in time in the master, there would've been a
scenario where the vacuum would've removed a tuple that would have been
visible to a newly starting transaction. Which can't happen. I think..
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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