| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Dan Ports <drkp(at)csail(dot)mit(dot)edu>, Florian Pflug <fgp(at)phlo(dot)org>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: SSI and Hot Standby |
| Date: | 2011-01-21 15:32:01 |
| Message-ID: | 10201.1295623921@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Fri, 2011-01-21 at 11:19 +0200, Heikki Linnakangas wrote:
>> It's not the order in which the xid was assigned that matters, but the
>> order the transactions started and got their snapshots. The xids might
>> be assigned a lot later, after the transactions have already read data.
> So if a read-write transaction assigns an xid before it takes a snapshot
> then we'll be OK? That seems much easier to arrange than passing chunks
> of snapshot data backwards and forwards. Optionally.
No, that idea is DOA from a performance standpoint. We sweated blood to
avoid having to assign XIDs to read-only transactions, and we're not
going back. If SSI requires that, SSI is not getting committed.
regards, tom lane
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