| From: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | Peter Eisentraut <peter_e(at)gmx(dot)net>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Tatsuo Ishii <ishii(at)postgresql(dot)org>, robertmhaas(at)gmail(dot)com, pgsql(at)j-davis(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, markus(at)bluegap(dot)ch, masao(dot)fujii(at)gmail(dot)com, aidan(at)highrise(dot)ca, heikki(dot)linnakangas(at)enterprisedb(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Sync Rep: First Thoughts on Code |
| Date: | 2008-12-15 21:40:44 |
| Message-ID: | 4946CEDC.1040700@cheapcomplexdevices.com |
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| Lists: | pgsql-hackers |
Josh Berkus wrote:
>
> Hmmm. I thought this was pretty clear. There's three levels of synch
> which are useful features:
>
> 1) "synchronus" standby which is really asynchronous, but only has a gap
> of < 100ms.
>
> 2) Synchronous standby which guarentees that all committed transactions
> are on the failover node and that no data will be lost for failover, but
> the failover node is still in standby mode.
>
> 3) Synchronous replication where the standby node has identical
> transactions to the master node, and is queryable read-only.
>
> Any of these levels would be useful....
Isn't the "queryable read-only" feature totally orthogonal with
how synchronous the replication is?
For one reporting system I have, where new data is continually
being added every second; I'd love to have a read-only-slave
even if that system has the "100ms" gap you mentioned in #1.
Heck I don't care if the queries it runs even have a 100 *minute*
gap; but I sure would like it to be synchronous in the sense
that all the transactions to survive a failure of the primary.
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