| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: max_standby_delay considered harmful |
| Date: | 2010-05-04 02:45:10 |
| Message-ID: | 201005040245.o442jAg15359@momjian.us |
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| Thread: | |
| Lists: | pgsql-hackers |
Simon Riggs wrote:
> On Mon, 2010-05-03 at 13:13 -0400, Stephen Frost wrote:
>
> > Perhaps you could speak to the specific user
> > experience difference that you think there would be from this change?
>
> The difference is really to do with the weight you give to two different
> considerations
>
> * avoid query cancellations
> * avoid having recovery fall behind, so that failover time is minimised
>
> Some people recognise the trade-offs and are planning multiple standby
> servers dedicated to different roles/objectives.
I understand Simon's point that the two behaviors have different
benefits. However, I believe few users will be able to understand when
to use which.
As I remember, 9.0 has two behaviors:
o master delays vacuum cleanup
o slave delays WAL application
and in 9.1 we will be adding:
o slave communicates snapshots to master
How would this figure into what we ultimately want in 9.1?
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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