| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | 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 21:06:15 |
| Message-ID: | 4946C6C7.5090001@agliodbs.com |
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| Lists: | pgsql-hackers |
Peter Eisentraut wrote:
> Simon Riggs wrote:
>> I am truly lost to understand why the *name* "synchronous replication"
>> causes so much discussion, yet nobody has discussed what they would
>> actually like the software to *do*
>
> It's the color of the bikeshed ...
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 and allow a certain number of our
users to deploy PostgreSQL in an environment where it wasn't used
before. So if we can only do (2) for 8.4, that's still very useful for
telecoms and banks.
--Josh
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