Add to replication.

doc/TODO.detail/replication

@@ -43,7 +43,7 @@ From owner-pgsql-hackers@hub.org Fri Dec 24 10:01:18 1999
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@@ -129,7 +129,7 @@ From owner-pgsql-hackers@hub.org Fri Dec 24 18:31:03 1999
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@@ -212,7 +212,7 @@ From owner-pgsql-hackers@hub.org Fri Dec 24 21:31:10 1999
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@@ -486,7 +486,7 @@ From owner-pgsql-hackers@hub.org Sun Dec 26 08:31:09 1999
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@@ -909,7 +909,7 @@ From owner-pgsql-hackers@hub.org Thu Dec 30 08:01:09 1999
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@@ -1006,7 +1006,7 @@ From owner-pgsql-patches@hub.org Sun Jan  2 23:01:38 2000
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@@ -1424,7 +1424,7 @@ From owner-pgsql-hackers@hub.org Tue Jan  4 10:31:01 2000
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@@ -4887,3 +4887,165 @@ TIP 6: Have you searched our list archives?
 
 http://www.postgresql.org/search.mpl
 
+From pgsql-hackers-owner+M9997@postgresql.org Wed Jun 13 09:05:56 2001
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+Message-ID: <11C1E6749A55D411A9670001FA687963368322@sdexcsrv1.f000.d0188.sd.spardat.at>
+From: Zeugswetter Andreas SB  <ZeugswetterA@wien.spardat.at>
+To: "'reinoud@xs4all.nl'" <reinoud@xs4all.nl>, pgsql-hackers@postgresql.org
+Subject: AW: AW: AW: [HACKERS] Postgres Replication
+Date: Wed, 13 Jun 2001 11:55:48 +0200
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+
+> Well as I read back the thread I see 2 different approaches to
+> replication:
+> 
+> 1: tight integrated replication. 
+> pro:
+> - bi-directional (or multidirectional): updates are possible everywhere
+> - A cluster of servers allways has the same state. 
+> - it does not matter to which server you connect
+> con:
+> - network between servers will be a bottleneck, especially if it is a
+> WAN connection
+> - only full replication possible
+
+I do not understand that point, if it is trigger based, you 
+have all the flexibility you need. (only some tables, only some rows,
+different rows to different targets ....), 
+(or do you mean not all targets, that could also be achieved with triggers)
+
+> - what happens if one server is down? (or the network between) are
+> commits still possible
+
+No, updates are not possible if one target is not reachable, 
+that would not be synchronous and would again need business rules
+to resolve conflicts.
+
+Allowing updates when a target is not reachable would require admin 
+intervention.
+
+Andreas
+
+---------------------------(end of broadcast)---------------------------
+TIP 4: Don't 'kill -9' the postmaster
+
+From pgsql-hackers-owner+M10005@postgresql.org Wed Jun 13 11:15:48 2001
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+	Wed, 13 Jun 2001 10:43:41 -0400
+From: Darren Johnson <djohnson@greatbridge.com>
+Date: Wed, 13 Jun 2001 14:44:11 GMT
+Message-ID: <20010613.14441100@j2.us.greatbridge.com>
+Subject: Re: AW: AW: AW: [HACKERS] Postgres Replication
+To: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
+cc: "'reinoud@xs4all.nl'" <reinoud@xs4all.nl>, pgsql-hackers@postgresql.org
+Reply-To: Darren Johnson <djohnson@greatbridge.com>
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+
+> > - only full replication possible
+
+> I do not understand that point, if it is trigger based, you
+> have all the flexibility you need. (only some tables, only some rows,
+> different rows to different targets ....),
+> (or do you mean not all targets, that could also be achieved with 
+triggers)
+
+Currently with Postgres-R, it is one database replicating all tables to 
+all servers in the group communication system.  There are some ways 
+around
+this by invoking the -r option when a SQL statement should be replicated, 
+and leaving the -r option off for non-replicated scenarios.  IMHO this is
+not a good solution.  
+
+A better solution will need to be implemented, which involves a 
+subscription table(s) with relation/server information.  There are two
+ideas for subscribing and receiving replicated data.
+
+1) Receiver driven propagation - A simple solution where all 
+transactions are propagated and the receiving servers will reference
+the subscription information before applying updates.
+
+2) Sender driven propagation - A more optimal and complex solution 
+where servers do not receive any messages regarding data items for 
+which they have not subscribed
+
+
+> > - what happens if one server is down? (or the network between) are
+> > commits still possible
+
+> No, updates are not possible if one target is not reachable,
+
+AFAIK, Postgres-R can still replicate if one target is not reachable,
+but only to the remaining servers ;).  
+
+There is a scenario that could arise if a server issues a lock 
+request then fails or goes off line.  There is code that checks 
+for this condition, which needs to be merged with the branch we have.
+
+> that would not be synchronous and would again need business rules
+> to resolve conflicts.
+
+Yes the failed server would not be synchronized, and getting this
+failed server back in sync needs to be addressed.
+
+> Allowing updates when a target is not reachable would require admin
+> intervention.
+
+In its current state yes, but our goal would be to eliminate this
+requirement as well.
+
+
+
+Darren
+
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