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From Michael Dürig <mdue...@apache.org>
Subject Re: MongoMK: deleted nodes
Date Thu, 10 Jan 2013 10:26:54 GMT

Hi,

This is only loosely related but, checking for nodes which don't exist 
is expensive across the stack. It currently always results in a full 
round trip. I think we should at some point come up with some kind of 
negative cache. Using a bloom filter for this would only add very little 
memory overhead but might save us quite some round trips.

Michael

On 10.1.13 10:07, Marcel Reutegger wrote:
> Hi,
>
> I was just thinking the way how MongoMK handles deleted nodes and
> I'm wondering if we should change it to make reading nodes less expensive.
>
> I understand reading a node requires checking all ancestors of that node
> to find out if it really exists. This is already done that way in NodeExistsCommand
> but it looks like it's missing in FetchNodesActionNew. To me it looks like
> we will have to change FetchNodesActionNew accordingly. But that means
> reading will become quite expensive.
>
> Would it be better to mark a node as deleted in the revision it was deleted?
> Reading a node in a given revision would return the node and we'd have to
> add logic to check the new flag. But we'd then immediately know whether
> the node exists in that revision without consulting ancestor nodes.
>
> regards
>   marcel
>

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