| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Kevin Grittner <kevin(dot)grittner(at)wicourts(dot)gov>, joe <joe(at)mcknight(dot)de>, noah <noah(at)leadboat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Snapshot synchronization, again... |
| Date: | 2011-02-22 00:00:19 |
| Message-ID: | 9087.1298332819@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Actually this seems rather difficult to do, because in order to invoke
> the function that imports the snapshot, you have to call SELECT, which
> acquires a snapshot beforehand. So when we actually import the
> passed-in snapshot, there's already a snapshot set. This is odious but
> I don't see a way around that -- other than adding special grammar
> support which seems overkill.
No, I don't think it is. The alternative is semantics that are
at least exceedingly ugly, and very possibly flat-out broken.
To take just one point, you have no way at all of preventing the
transaction from having done something else using its original
snapshot.
regards, tom lane
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