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:[EMAIL PROTECTED] > Sent: Tuesday, February 01, 2005 2:43 PM > To: Derby Development > Subject: Re: Derby architecture/design documents > > > From: "Suresh Thalamati" <[EMAIL PROTECTED]> > > > >>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 > > >
smime.p7s
Description: S/MIME cryptographic signature
