I was thinking along the same lines. However, having 2 standby servers is a must for us. If my colocation center gets razed to the ground, I need to have a standby server elsewhere. Having one at the colocation center is for soft/hardware disasters on any primary. Having one at my office is for facility disasters at the colocation center. I envision it working like this: The archive command pseudocode will be: rsync <mywalfile> someone@abox The standby slave servers will then continually rsync that directory while in recovery mode. Reading the docs, it looks as if this should work. It's also my understanding that the archive command happens asynchronously, so it shouldn't affect the overall performance of the primary. Regardless, my proposed solution should handle such a scenario. -----Original Message----- From: Montaseri [mailto:montaseri@xxxxxxxxx] Sent: Jun 26, 2008 1:21 PM To: Scott Whitney Cc: Simon Riggs; pgsql-admin@xxxxxxxxxxxxxx Subject: Re: [ADMIN] Warm standby server While I am not an expert on WAL, but again I question the merits of such sophisticated HA configuration. Of course there are use cases for such configs, but I am only advocating best price performance kind of mentality As WAL writes the journals all the way down to the disk (ie write thru and not write behind) before ack-ing toward the next step in a DB operation, increasing the number of mirrors (one production, one on-site, one off-site, I count 3 plexes here) will prolong each operation, with the following exponentially increasing write latencies production DB writes are at the rate of SCSI, SATA or system bus (30 MBps) on-site DB writes are at the rate of LAN (10 MBps) off-site DB writes are at the rate of WAN (200 KBps) Then if a three-way WAL writes is considered completed after the last WAN write, then you have effectively lowered your performance to 200 KBytes per sec writes. Now the gain. If the building gets destroyed, my data is protected. Ok. what kind of business are we running in that building? .... what is the rate of writes to database vs probability of building coming down vs value of data from 2 hours ago vs 10 seconds ago. Thanks Medi On Thu, Jun 26, 2008 at 11:01 AM, Scott Whitney <swhitney@xxxxxxxxxxx> wrote: Fully agreed, and it's just a concept at the moment. After I have a prototype standby working next week in the first place, we'll be discussing those very merits. A 2nd question: Is it possible to have 2 standby servers with a single master duplicating to standby1 (at my coloc), and standby2 (at my office)? Assume no auto-failover. -----Original Message----- From: Montaseri [mailto:montaseri@xxxxxxxxx] Sent: Jun 26, 2008 12:51 PM To: Simon Riggs Cc: Scott Whitney; pgsql-admin@xxxxxxxxxxxxxx Subject: Re: [ADMIN] Warm standby server I am not so sure of this arrangement's mertis From HA (High Availability) point of view, the host/server is a single point of failure which will bring your entire infrastructure down if any of the server hardware components fail. From Performance point of view, you have increased the load on your server by 3 folds as all instances would be using your I/O bandwidth to write to secondary storage Given $300 to $400 price of headless servers these days, its much economical to split the workload on three boxes Cheers Medi On Thu, Jun 26, 2008 at 9:06 AM, Simon Riggs <simon@xxxxxxxxxxxxxxx> wrote: On Thu, 2008-06-26 at 10:19 -0500, Scott Whitney wrote: > I've got 3 different database servers (db01, db02 and db03). > > I would like to have a WAL standby server that replays logs for all 3 in > case one goes down, so I can promote that particular server. > > Can I do this by installing 3 separate postmasters on this machine? > Obviously, if 2 went down at the same time, I'd have to do some magic to > bring up another machine, but I'm not sure that's a concern. Yes, that will work. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
