| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
| Cc: | Noah Misch <noah(at)leadboat(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < |
| Date: | 2016-07-19 23:32:50 |
| Message-ID: | 20160719233250.nir5vyvzef7m4e7z@alap3.anarazel.de |
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On 2016-07-19 18:09:59 -0500, Kevin Grittner wrote:
> As far as I can see, to do this the way that Andres and Amit
> suggest involves tying in to indexam.c and other code in incredibly
> ugly ways.
Could you explain the problem you're seing?
Isn't pretty much all all that we need to do:
1) add a InitSnapshotToast(Snapshot originMVCCSnap), which sets SnapshotData->lsn
to the the origin snapshot's lsn
2) adapt TestForOldSnapshot() to accept both HeapTupleSatisfiesMVCC and
HeapTupleSatisfiesToast?
I mean the only difference between toast / plain heap table WRT
old_snapshot_threshold is that we don't use a mvcc snapshot.
> I think it is entirely the wrong way to go, as I can't
> find a way to make it look remotely sane. The question is whether
> I should do it the way that I think is sane, or whether someone
> else wants to show me what I'm missing by producing at least a
> rough patch along these lines.
I'll, but I'd prefer you explaining the problem first. Maybe it's me
missing the obvious problem.
Andres
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