From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200208171219.g7HCJZk22900@candle.pha.pa.us>
Subject: Re: [INTERFACES] libpgtcl modifications
In-Reply-To: <3D59F2F3.1030904@inode.at>
To: Gerhard Hintermayer <g.hintermayer@inode.at>
Date: Sat, 17 Aug 2002 08:19:35 -0400 (EDT)
Cc: PostgreSQL-patches <pgsql-patches@postgresql.org>
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Your patch has been added to the PostgreSQL unapplied patches list at:

	http://candle.pha.pa.us/cgi-bin/pgpatches

I will try to apply it within the next 48 hours.

---------------------------------------------------------------------------


Gerhard Hintermayer wrote:
> Bruce Momjian wrote:
> > Can I have some description of what this patch does?
> >
> 
> Unfortunately some of my postings seem to vanish in cyberspace ;-)
> 
> What I have done for libpgtcl:
> Everytime if I do PQconsumeInput (when the backend channel gets
> readable) I check for the return value. (0 == error) and generate a
> notification manually, e.g. fixed string connection_closed) and pass it to the 
> TCL event queue. The only other thing I had to do is to comment out removing
> all pending events in PgStopNotifyEventSource whenever the connection was
> unexpectedly closed (so the manually generated event will not be deleted).
> 
> A broken backend connection triggers a notify event to the client (fixed 
> notification string "connection_closed") so proper action can be taken to switch 
> to another database server etc. Remember that this is event driven. If you have 
> applications, that have idle database connections most of the time, you'll get 
> immediate feedback of a dying server. Upon connection to the server issue a 
> pg_notify for notify event "connection_closed" and whenever the backend crashes 
> (which it does do in very very rare cases) you get an event driven recovery. (of 
> course the Tcl-Event loop has to be processed). Issuing a notification 
> "connection_closed" on a still working database could be used for switching to 
> another db-server (which I've actually impelemented right now).
> 
> I did this not because we have crashing db-servers all the time, in fact we have 
> running pg for many years without any major problems in a production environment
> (recipe and batch data for petfood production).
> One reason was to get notifications to applications, that run permanently and 
> have a persistent db connection, in case the primary server should be changed 
> for whatever reason (network problems, server shutdown, maintenance etc.)
> 
> Gerhard.
> 
> PS:
>  >[ application/x-gunzip is not supported, skipping... ]
> are you joking, which file format do you suggest for a patch ?
> 
> 
> -- 
> Gerhard Hintermayer
> http://www.inode.at/g.hintermayer
> 
> 

-- 
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