Thanks to all for your help. I've adopted the scheme involving a
"staging" table -- the writer processes insert into that, then a single
"publisher" process pulls from that and writes to the log, giving a
clean serial order for any reader of the log.
Vance
On Mon, 2008-04-21 at 23:59 +0200, Joris Dobbelsteen wrote:
> Craig Ringer wrote:
> [snip]
> > If you really want to make somebody cry, I guess you could do it with
> > dblink - connect back to your own database from dblink and use a short
> > transaction to commit a log record, using table-based (rather than
> > sequence) ID generation to ensure that records were inserted in ID
> > order. That'd restrict the "critical section" in which your various
> > transactions were unable to run concurrently to a much shorter period,
> > but would result in a log message being saved even if the transaction
> > later aborted. It'd also be eye-bleedingly horrible, to the point where
> > even the "send a message from a C function" approach would be nicer.
>
> This will not work for the problem the TS has. Let a single transaction
> hang for a long enough time before commit, while others succeed. It will
> keep ordering of changes, but commits might come unordered.
>
> The issue is, you don't really have the critical section as you
> describe, there is no SINGLE lock you are 'fighting' for.
>
> It will work with an added table write lock (or up), that will be the
> lock for your critical section.
>
> In my opinion I would just forget about this one rather quickly as you
> more or less proposed...
>
> - Joris
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