Proposal for alternate way to traverse BKD tree with prefetching matching leaves for IO concurrency

[abiesps]

Description

I would appreciate feedback on BKD traversal with prefetching.

At a high level, this is what I am doing:

Start traversing the BKD tree as is,

If cell is inside the query
a) Call goes to prepareDocIDs method variation where if isLeaf is true.
b) Do not read the leaf node yet. Instead, get the leafOrdinal, if this leaf ordinal is in continuation to last matching leaf ordinal (which I am storing in visitor) i.e leafOrdinal == visitor.lastMatchingLeafOrdinal() + 1. Do not call prefetch as this should be hopefully taken care by kernel readaheads. Otherwise if its not a continuous match i.e leafOrdinal != visitor.lastMatchingLeafOrdinal() + 1, then call prefetch on this leaf node file pointer. Also store this leaf node fp in visitor for visting matching doc IDs later.
c) If its not a leafNode continue with recursion as is.
d) Visit the cached leaf node file pointers after recursion.

For remaining traversal code remains unchanged.

Related Issue

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