Re: why not kill -9 postmaster

Shane Ambler wrote:
> Dawid Kuroczko wrote:
> >On 10/20/06, Shane Ambler <pgsql@007marketing.com> wrote:
>
> >>The one thing worse than kill -9 the postmaster is pulling the power
> >>cord out of the server. Which is what makes UPS's so good.
> >
> >
> >Well, I think that pulling the power cord is much safer than killing -9
> >the postmaster.  If you pull the plug, then during bootup postgresql
> >will just replay every COMMITed transaction, so there won't be any
> >dataloss or downtime.
>
> If you kill -9 the postmaster the system can still finish sending
> changes to disk and close the file but pulling the power cord can stop a
> write in the middle of a block giving you half new data and half old
> data in the one file.

That case is protected against in the WAL code.  That's what we save
whole page images for.

The only difference between kill -9 postmaster and abrupt shutdown, is
that on the former case there may be backends that continue to run and
commit transactions.  Those will still be WAL-logged though.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.