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https://issues.apache.org/jira/browse/CASSANDRA-6271?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benedict updated CASSANDRA-6271:
--------------------------------
Description:
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.
I suggest using a sorted array; changes are supplied at-once, as opposed to one
at a time, and if < 10% of the values 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.
was:
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.
I suggest using a sorted array; changes are supplied at-once, as opposed to one
at a time, and if < 10% of the values in the array change 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.
> 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
>
> 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.
> I suggest using a sorted array; changes are supplied at-once, as opposed to
> one at a time, and if < 10% of the values 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.
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