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From: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>
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Subject: Re: [Qemu-devel] [RFC V8 01/24] qcow2: Add journal specification.
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>, kwolf@redhat.com, qemu-devel@nongnu.org

> Does this mean the journal forms the first-stage data structure for
> deduplication?  Dedup records will accumulate in the journal until it
> becomes time to convert them in bulk into a more compact representation?

The journal is mainly used to persist the last inserted dedup metadata across
QEMU stop and restart. I replay it at startup to rebuild the hash table.
So yes it's the first stage even it's never used for regular queries.

> 
> When I read this specification I was thinking of a journal purely for
> logging operations.  You could use a commit record to mark previous
> records applied.  Upon startup, qcow2 would inspect uncommitted records
> and deal with them.

Maybe that could help regular QCOW2 usage. I don't know.