| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposal for 9.1: WAL streaming from WAL buffers |
| Date: | 2010-06-12 01:10:18 |
| Message-ID: | 4C12DE7A.6060009@agliodbs.com |
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| Lists: | pgsql-hackers |
> Hm, but then Robert's failure case is real, and streaming replication might break due to an OS-level crash of the master. Or am I missing something?
Well, in the failover case this isn't a problem, it's a benefit: the
standby gets a transaction which you would have lost off the master.
However, I can see this as a problem in the event of a server-room
powerout with very bad timing where there isn't a failover to the standby:
1) Master goes out
2) "floating" transaction applied to standby.
3) Standby goes out
4) Power back on
5) master comes up
6) standby comes up
It seems like, in that sequence, the standby would have one transaction
which the master doesn't have, yet the standby thinks it can continue
getting WAL from the master. Or did I miss something which makes this
impossible?
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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