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Re: high (or at least improved) availability and failover

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Iain <iain(at)mst(dot)co(dot)jp>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: high (or at least improved) availability and failover
Date: 2004-11-27 04:15:30
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Lists: pgsql-admin
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Iain wrote:
> HI,
> I've been looking into options for improving the availability of postgres 
> servers beyond what you get with a monolithic server and RAID. These are, as 
> far as possible "cheap" options and therefore don't include use of shared 
> storage and all the good options those systems have.
> Here is a very rough summary of my thoughts so far. I havn't actually tried 
> any of this yet, so if anyone has any thoughts, comments, additions I'd be 
> glad to hear from you.
> regards
> iain
> Configurations for HA
> =====================
> Pgpool Only
> -----------
> Pgpool can detect the failure of a server and failover automatically.
> Re-syncing the DBs after a failure will require the databases to be offline 
> for a file system copy.
> Should pgpool run on the db servers or a separate machine(s)?
> Performance impact of using the replication facility? Deadlock possibility?
> If the machine that pgpool is running on fails, need manual intervention to 
> start pgpool on another machine.
> Can only manage 2 servers at most.
> Pgpool and Heartbeat
> -----------------
> Similar to pgpool only, with the addition that pgpool itself can be failed 
> over automatically.
> Heartbeat and DRDB
> ---------------
> Replication is done at the block level by DRDB.
> The database cannot be running on the standby server while it is being 
> replicated from the master.
> Automatic failover is possible as Heartbeat will start the database server 
> and switch to the standby if the master fails.
> A full re-sync of the DBs after a failure doesn't require the master to be 
> offline.
> Failure ofthe standby server typically doesn't require a full re-sync.
> Can't do load balancing.
> No particular need for pgpool as heartbeat will manage the aliased IP 
> address
> Slony-I only
> ------------
> Relies on triggers in the database, and some administration of the 
> replication configuration.
> Monitors replicated databases and performs automatic failover.
> When a failed server is brought back online it will automatically start 
> catching up with the other servers.
> When the master fails, clients can reconnect to the new master without 
> changing the IP address?
> Slony-I and pgpool
> ---------------
> All the features of Slony-I
> Some load balancing of SELECT SQL is possible
> Need manual intervention if pgpool fails.
> Slony-I and pgpool and Heartbeat
> ----------------------------
> All the features of Slony-I with pgpool
> Use heartbeat to monitor the machines running pgpool and switch over 
> automatically if one fails.

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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