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From "Branimir Lambov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9769) Improve BTree
Date Wed, 15 Jul 2015 10:21:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9769?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14627855#comment-14627855
] 

Branimir Lambov commented on CASSANDRA-9769:
--------------------------------------------

+1

[BTree.compare|https://github.com/apache/cassandra/commit/5e4c3190666f8e3e9fed5516eab32771ae66bf86#diff-4b911b7d0959c6219175e2349968f3cdR725]:
It's a bit simpler if you think what you want to return:
{code}
if (a == NEGATIVE_INFINITY || b == POSITIVE_INFINITY)	// also true for a==b \in {-inf, +inf}
    return (a == b) ? 0 : -1;
if (a == POSITIVE_INFINITY || b == NEGATIVE_INFINITY)
    return 1;
{code}

> Improve BTree
> -------------
>
>                 Key: CASSANDRA-9769
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9769
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>             Fix For: 3.0 beta 1
>
>
> Split out from CASSANDRA-9471, after discussion there. This patch contains all of the
btree centric changes, as well as some minimally invasive replacement of TreeMap around the
codebase.
> * Introduces "indexing" to the BTree class, permitting lookup by positional index, and
binarySearch semantics (so inequality lookups yield the position a binarySearch of the equivalent
array would)
> ** The size modulo remainder of a Leaf/Branch are flipped, so that a Branch has a spare
slot at the end for an int[] index:
> *** if missing, this occupies at most 1 bit per entry in the set (often 1/32), if present,
it occupies at most 2.5 bits, and typically around 1 bit. Sets with <= 32 items incur no
cost.
> *** This index just contains the cumulative size of the tree preceding each branch key,
rooted at the node in question
> * Reintroduces BTreeSet, with extra methods for accessing by index*, and simple implementations
of missing NavigableMap methods using this new functionality
> * Introduces a simple BTreeSet.Builder, and replaces all suitable uses of TreeMap in
the codebase with a BTreeSet.Builder -> BTreeSet
> * Rewrites btree.Cursor to make it far easier to understand, and to introduced IndexedSearchIterator,
exposing the new indexing
> * Reintroduces LongBTreeTest, with cleaned up more exhaustive coverage of iterator functionality,
and new NavigableMap methods
> This version further cleans up a few things, and switches to always indexing a btree,
given the costs are fairly low (which permits eliminating quite a bit of code that would be
required if the positions of items were not known, and providing just one iterator implementation)



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