commit c9552abaf3286f5b277d64f78c46020fe3978aa3
author Ivan Frade <ifrade@google.com> Tue Dec 14 16:36:54 2021 -0800
committer Ivan Frade <ifrade@google.com> Tue Feb 14 11:50:29 2023 -0800
tree 272d4facf548e8bec1e84c9c18670cb5ecc4867d
parent 62d0e7be7c2a3c72e50dd9474ea72dfd7ec586b9

PackObjectSizeIndex: interface and impl for the object-size index

Operations like "clone --filter=blob:limit=N" or the "object-info"
command need to read the size of the objects from the storage. An
index would provide those sizes at once rather than having to seek in
the packfile.

Introduce an interface for the Object-size index. This index returns
the inflated size of an object. Not all objects could be indexed (to
limit memory usage).

This implementation indexes only blobs (no trees, nor
commits) *above* certain size threshold (configurable). Lower
threshold adds more objects to the index, consumes more memory and
provides better performance. 0 means "all blobs" and -1 "disabled".

If we don't index everything, for the filter use case is more
efficient to index the biggest objects first: the set is small and
most objects are filtered by NOT being in the index. For the
object-size, the more objects in the index the better, regardless
their size. All together, it is more helpful to index above threshold.

Change-Id: I9ed608ac240677e199b90ca40d420bcad9231489