Sameer Abhyankar has posted comments on this change.

Change subject: KUDU-1363: Add in-list predicates for extracting a set of 

Patch Set 7:

> > The main reason for not using unordered_set was because the
 > > collection would still be storing pointers instead of actual
 > values
 > > and I did not think I could get an O(1) lookup when i am
 > searching
 > > for a pointer-to-a-value in a set-of-pointers. PredicateData
 > doesnt
 > > know about the the type of the value and defers the comparison to
 > > TypeInfo. As a result, PredicateData only holds void* or a
 > > collection(vector) of void*.
 > >
 > > The other (not so critical) reason I went with a vector vs an
 > > unordered_set was because I do care about the order of the list
 > > (which is sorted/deduped) when I push Upper/Lower bound key
 > > predicates in key_util. I suppose, I could sort and pick the
 > > min/max values from the collection in key_util itself instead of
 > > using a vector. However, using a vector just made it convenient.
 > Your second point is a valid one; std::unordered_set would be
 > inappropriate if you need to find lower/upper bounds often (I think
 > this happens in the predicate pushdown code that I didn't review).
 > But what about std::set? It's implemented by a red-black tree and
 > so it'd still be more efficient than std::vector.
 > As to your first point, whichever container you use, you can pass a
 > custom hash and equal_to (for unordered_set) or comparator (for
 > set) that workers properly for KuduValue pointers. The
 > implementation would dereference the pointer, dereference the
 > private Data pointer inside it, and, using the definition of
 > KuduValue::Data in value-internal.h, operate on the actual data.

OK..let me take a look at it today.

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Gerrit-MessageType: comment
Gerrit-Change-Id: I986cb13097f1cf4af2b752f58c4c38f412a6a598
Gerrit-PatchSet: 7
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: Sameer Abhyankar <>
Gerrit-Reviewer: Adar Dembo <>
Gerrit-Reviewer: Dan Burkert <>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Sameer Abhyankar <>
Gerrit-Reviewer: Todd Lipcon <>
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