| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: New trigger option of pg_standby |
| Date: | 2009-04-10 16:31:43 |
| Message-ID: | 1239381103.16396.30.camel@ebony.2ndQuadrant |
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| Lists: | pgsql-hackers |
Fujii-san,
I like the new patch using the content of the file to determine the
mode. Much easier to use at failover time.
On Fri, 2009-04-10 at 12:47 +0900, Fujii Masao wrote:
> > One problem with this patch is that in smart mode, the trigger file is not
> > deleted. That's different from current pg_standby behavior, and makes
> > accidental failovers after one failover more likely.
>
> Yes, it's because pg_standby cannot be sure when the trigger file
> can be removed in smart mode. If the trigger file is deleted as soon
> as it's found, just like in fast mode, pg_standby may keep waiting
> for WAL file again.
My understanding of smart mode is fairly simple:
if (triggered)
{
if (smartMode && nextWALfile+1 exists)
exit(0);
else
{
delete trigger file
exit(1);
}
}
If you perform a file lookahead (the +1) as shown above then you avoid
the problem Heikki observes.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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