| From: | Csaba Nagy <nagy(at)ecircle-ag(dot)com> |
|---|---|
| To: | Dimitri Fontaine <dfontaine(at)hi-media(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Richard Huxton <dev(at)archonet(dot)com> |
| Subject: | Re: Transaction Snapshots and Hot Standby |
| Date: | 2008-09-11 13:38:25 |
| Message-ID: | 1221140305.17270.100.camel@PCD12478 |
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| Lists: | pgsql-hackers |
On Thu, 2008-09-11 at 15:33 +0200, Dimitri Fontaine wrote:
> What would forbid the slave to choose to replay all currently lagging WALs
> each time it's given the choice to advance a little?
Well now that I think I understand what Heikki meant, I also think the
problem is that there's no choice at all to advance, because the new
queries will simply have the same snapshot as currently running ones as
long as WAL reply is blocked... further blocking the WAL reply. When
saying this I suppose that the snapshot is in fact based on the last
recovered XID, and not on any slave-local XID. In that case once WAL
recovery is blocked, the snapshot is stalled too, further blocking WAL
recovery, and so on...
Cheers,
Csaba.
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