[jira] [Commented] (CASSANDRA-9769) Improve BTree

["Benedict (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-9769?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14620256#comment-14620256 ] 

Benedict commented on CASSANDRA-9769:
-------------------------------------

It may be worth considering renaming {{BTree}} -> {{RawBTree}} and {{BTreeSet}} -> {{BTree}}, since {{BTreeSet}} now also implements {{List}}, which is a bit confusing. Or perhaps {{BTreeSet}} -> {{BTreeListSet}}. Haven't done this for the moment, as it isn't super important, would involve a lot of unnecessary diffs for review, and it's always worth discussing nomenclature first.

> 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)



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)