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From "Sylvain Lebresne (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2893) Add row-level isolation
Date Wed, 16 Nov 2011 14:19:51 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13151221#comment-13151221
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Sylvain Lebresne commented on CASSANDRA-2893:
---------------------------------------------

bq. Do we even have an insert test mode that can generate same-row contention?

I don't think so, but that would be useful, even outside of testing this.

bq. but young-gen garbage, which is close to free

I suppose it depends but I don't think it will be necessarily young-gen, on the contrary even.
The added garbage is that when we add new columns to a row already in the memtable, we'll
copy a number of nodes of the underlying SnapTree. But those old nodes are live since their
initial insertion and the new ones will be until the next insertion into this row (or longer,
we don't do a full copy). So this roughly depends of the average between two updates to the
same row in a memtable. Not totally sure it fits into a young-gen. That being I'm not particularly
worried.
                
> Add row-level isolation
> -----------------------
>
>                 Key: CASSANDRA-2893
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2893
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>             Fix For: 1.1
>
>         Attachments: 0001-Move-deletion-infos-into-ISortedColumns.patch, 0002-Make-memtable-use-CF.addAll.patch,
0003-Add-AtomicSortedColumn-and-snapTree.patch, snaptree-0.1-SNAPSHOT.jar
>
>
> This could be done using an the atomic ConcurrentMap operations from the Memtable and
something like http://code.google.com/p/pcollections/ to replace the ConcurrentSkipListMap
in ThreadSafeSortedColumns.  The trick is that pcollections does not provide a SortedMap,
so we probably need to write our own.
> Googling [persistent sortedmap] I found http://code.google.com/p/actord/source/browse/trunk/actord/src/main/scala/ff/collection
(in scala) and http://clojure.org/data_structures#Data Structures-Maps.

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