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From Marcel Reutegger <mreut...@adobe.com>
Subject RE: SegmentNodeStore merge operations
Date Thu, 07 Mar 2013 11:57:03 GMT
> On Thu, Mar 7, 2013 at 1:08 PM, Marcel Reutegger <mreutegg@adobe.com>
> wrote:
> > as mentioned before, I think snapshot isolation is just fined because
> > in most cases it is sufficient and allows for increased concurrency. for
> > the cases where more consistency guarantees are needed, like
> > unique UUIDs and hard references we should implement the
> > validators accordingly and e.g. use a technique like materializing the
> conflict.
> 
> That technique essentially serializes all commits that could possibly
> violate a global invariant.

not necessarily. e.g. if we take the unique UUID as an example,
two sessions can proceed concurrently when they create nodes
with different UUIDs, which is usually the case. the conflict only
materializes when you create two nodes with the same UUID.

> The SegmentMK can avoid such
> synchronization points entirely at the cost of potentially "undoing"
> some commits that become invalid later on.

doesn't this require knowledge about the internals of the global
invariant. how does the SegmentMK know what exactly it can undo?

regards
 marcel

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