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From "Philip Bohannon" <bohan...@lucent.com>
Subject RE: Derby architecture/design documents
Date Tue, 01 Feb 2005 20:04:17 GMT
I believe "crash recovery" means all volatile buffers and non-flushed disk
pages are lost, as well as, depending on your failure model, the total
contents of any physical disk page in the process of being written at the
time of the crash.

"Media recovery" means that we lost some part of the checkpoint, but we
have archived versions of the log, and some offline copy of an old
checkpoint.

If you lose your logs (and there is a crash), AFAIK, there is no hope to
recover information past the first loss, assuming it is after the most
recent checkpoint.

Also a desirable feature is "point in time recovery" against logical
corruption - i.e., some angry/confused user started deleting all the
customer records Monday morning.  Can I start with an old checkpoint and
run the recovery log until Sunday night to get some consistent state from
around that time back?  (This is usually straightforward to implement.)

Cheers,

Philip Bohannon
Computing Sciences Research Center
Lucent Technologies -- Bell Laboratories

> -----Original Message-----
> From: Dibyendu Majumdar [mailto:dibyendu@mazumdar.demon.co.uk]
> Sent: Tuesday, February 01, 2005 2:43 PM
> To: Derby Development
> Subject: Re: Derby architecture/design documents
>
>
> From: "Suresh Thalamati" <suresh.thalamati@gmail.com>
>
> >  >>Derby implements the Write Ahead Log using a non-circular file
system
> > file. At present, there is no support for incremental log backup or
> > media recovery. Only crash recovery is supported.
> >
> > I think derby does support simple media recovery.  It has support for
> > full backup/restore and very basic form of  rollforward recovery
(replay
> > of logs using backup and archived log files).
>
> Hi Suresh,
>
> Thanks for the feedback. I suppose that we should define media recovery
and
> crash recovery. My understanding is that media recovery is when you have
> lost your logs as
> well, whereas crash recovery is when the logs are intact. In case of
media
> recovery,
> does Derby know how to locate the last checkpoint record/log file?
>
> Regards
>
>
>

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