[
https://issues.apache.org/jira/browse/CASSANDRA-6271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13859136#comment-13859136
]
Benedict commented on CASSANDRA-6271:
-------------------------------------
bq. [junit] No runnable methods
Sorry, laziness on my part for not checking the ant for if we actually had a
long test runner, I was just running this through the main() method. I'll
refactor into an actual JUnit test and upload.
bq. This looks like we're second-guessing lower/upper bounds. Would prefer to
assert that lower is actually <= upper.
Actually, IIRC this is to deal with inclusive/exclusive bounds. Since we find
these using floor/ceil/higher/lower, we can actually end up in a position where
for empty result ranges we find the upper/lower bounds in the btree to be
either side of each other, even though the provided ranges were legal.
> Replace SnapTree in AtomicSortedColumns
> ---------------------------------------
>
> Key: CASSANDRA-6271
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6271
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Benedict
> Assignee: Benedict
> Labels: performance
> Attachments: oprate.svg
>
>
> On the write path a huge percentage of time is spent in GC (>50% in my tests,
> if accounting for slow down due to parallel marking). SnapTrees are both GC
> unfriendly due to their structure and also very expensive to keep around -
> each column name in AtomicSortedColumns uses > 100 bytes on average
> (excluding the actual ByteBuffer).
> I suggest using a sorted array; changes are supplied at-once, as opposed to
> one at a time, and if < 10% of the keys in the array change (and data equal
> to < 10% of the size of the key array) we simply overlay a new array of
> changes only over the top. Otherwise we rewrite the array. This method should
> ensure much less GC overhead, and also save approximately 80% of the current
> memory overhead.
> TreeMap is similarly difficult object for the GC, and a related task might be
> to remove it where not strictly necessary, even though we don't keep them
> hanging around for long. TreeMapBackedSortedColumns, for instance, seems to
> be used in a lot of places where we could simply sort the columns.
--
This message was sent by Atlassian JIRA
(v6.1.5#6160)
