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From "Paulo Motta (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-13299) Potential OOMs and lock contention in write path streams
Date Thu, 14 Sep 2017 10:09:02 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16166039#comment-16166039
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Paulo Motta edited comment on CASSANDRA-13299 at 9/14/17 10:08 AM:
-------------------------------------------------------------------

Thanks, the patch looks good from an initial look, great job! Some minor comments:
* Generalize {{ThrottledUnfilteredIterator}} since it can also be useful outside of streaming
package:
** Make {{ThrottledUnfilteredIterator}} an {{Iterator<UnfilteredRowIterator>}} instead
of using {{hasNextGroup}} and {{resetLimit}} which is analogous to {{hasNext}} and {{next}}.
** Move to {{org.apache.cassandra.db.rows}} package
** Add simple javadoc explaining what it does
** Move {{cassandra.mv.mutation.row.count}} out of {{ThrottledUnfilteredIterator}}, and maybe
rename it to {{cassandra.repair.mutation_repair_rows_per_batch}} (or similar, since it's also
used for CDC).
* Add unit test to {{ThrottledUnfilteredIterator}} to make sure it's generating range tombstones
correctly

dtest looks good!


was (Author: pauloricardomg):
Thanks, the patch looks good from an initial look, great job! Some minor comments:
* Generalize {{ThrottledUnfilteredIterator}} since it can also be useful outside of streaming
package:
** Make {{ThrottledUnfilteredIterator}} an {{Iterator<UnfilteredRowIterator>}} instead
of using {{hasNextGroup}} and {{resetLimit}} which is analogous to {{hasNext}} and {{next}}.
** Move to {{org.apache.cassandra.db.rows}} package
** Add simple javadoc explaining what it does
** Move {{cassandra.mv.mutation.row.count}} out of {{ThrottledUnfilteredIterator}}, and maybe
rename it to {{cassandra.repair.mutation_repair_rows_per_batch}} (or similar, since it's also
used for CDC).
* Add unit test to {{ThrottledUnfilteredIterator}} to make sure it's generating range tombstones
correctly

> Potential OOMs and lock contention in write path streams
> --------------------------------------------------------
>
>                 Key: CASSANDRA-13299
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13299
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benjamin Roth
>            Assignee: ZhaoYang
>
> I see a potential OOM, when a stream (e.g. repair) goes through the write path as it
is with MVs.
> StreamReceiveTask gets a bunch of SSTableReaders. These produce rowiterators and they
again produce mutations. So every partition creates a single mutation, which in case of (very)
big partitions can result in (very) big mutations. Those are created on heap and stay there
until they finished processing.
> I don't think it is necessary to create a single mutation for each partition. Why don't
we implement a PartitionUpdateGeneratorIterator that takes a UnfilteredRowIterator and a max
size and spits out PartitionUpdates to be used to create and apply mutations?
> The max size should be something like min(reasonable_absolute_max_size, max_mutation_size,
commitlog_segment_size / 2). reasonable_absolute_max_size could be like 16M or sth.
> A mutation shouldn't be too large as it also affects MV partition locking. The longer
a MV partition is locked during a stream, the higher chances are that WTE's occur during streams.
> I could also imagine that a max number of updates per mutation regardless of size in
bytes could make sense to avoid lock contention.
> Love to get feedback and suggestions, incl. naming suggestions.



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