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From Alex Karasulu <akaras...@gmail.com>
Subject Re: [DRS] thoughts about implementation
Date Tue, 03 Feb 2009 19:30:39 GMT
On Tue, Feb 3, 2009 at 2:19 PM, Kiran Ayyagari <ayyagarikiran@gmail.com>wrote:

>
> Hi Alex,
>
>  I'm seriously thinking the use of the CL for a journal is not a good
>> decision. The journal needs to be fast and simple, doing only one thing and
>> doing it fast and flawlessly.
>>
> +1, by 'replica of CL' I mean the journal contains the same data what CL
> stores in its store minus the indices and journal just writes that data in a
> sequential order (CL could be a B-Tree).


Right I agree the CL is fine as it is with the B-Tree and indices.  The
journal need not be a btree if all we need is sequential access.  We merely
need a simple pointer or two into it to know where the last operation was
successfully processed.  Hence everything earlier or after it in the file
represents currently active operations.


>
> However an assumption I made here was that each valid operation succeeds at
> least before storing its data in CL
> ( we have to write the same data to journal before storing in CL) this way
> we no longer need any marking operation cause
> if the master db gets corrupted we use CL to restore and if the CL also
> gets corrupted then we can restore the CL from
> journal(start from the beginning hence no intermediate 'marks') and then
> restore the master db.
>

I agree that *ONLY* change operations that have succeeded should be logged
into the CL.  But I think we at least need a marker in the journal to track
the horizon between completed and in progress operations no?

Alex

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