From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: How to check whether the row was modified by this transaction before? |
Date: | 2012-12-06 19:08:50 |
Message-ID: | 20121206190850.GE20926@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2012-12-06 13:59:32 -0500, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On 2012-12-06 15:08:51 -0300, Alvaro Herrera wrote:
> >> Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru> writes:
> >>> In a BEFORE UPDATE trigger I need to know whether the row was previously
> >>> modified by this transaction. Is it safe to use xmin and txid_current()
> >>> for this purpose (xmin is 32-bit txid type but txid_current() returns
> >>> 64-bit bigint).
>
> > I wonder if we shouldn't have a function txid_is_current(xid);
>
> Yeah, I was wondering that too, and wanted to know if the OP had a
> use-case that was mainstream enough to justify adding such a function.
I think architectures with an invalidation-queue to external caches (be
it web-proxies or something lower-level) are quite popular. And with the
new NOTIFY or pgq relatively simple. Ad to those its sensible not to
post a single primary key more than once.
Magnus had talks about specifically that on various conferences if that
counts as anything ;)
Mainstreamy enough?
Andres
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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