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From Marcel Reutegger <mreut...@adobe.com>
Subject [MongoMK] flag document with children
Date Thu, 24 Oct 2013 07:35:28 GMT

yesterday Chetan, Thomas and I discussed an access pattern Chetan
saw with the MongoMK. Installing a vlt package shows many reads on
MongoDB for children of nodes that do not have child nodes. these
nodes are the leafs of the tree. due to the current content model, 
the MongoMK does not know if a node has children, by just looking
at the NodeDocument for that node. we then quickly discussed that
we could mark the leaf nodes once we discover that it is a leaf.

I was thinking about this a bit more and came to the conclusion that
it is probably better to mark the nodes with children, instead of the
leaf nodes. there are a number of advantages:

- it works better with concurrent writes. once set, it usually does not
change back unless the MongoMK GC actually removes a document
in MongoDB.
- less storage overhead. there are usually fewer parents than leaf nodes.
- it does not have to be 100% accurate. false positives are OK (document
says it has children, but then returns none).



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