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From "Nate McCall (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-13299) Potential OOMs and lock contention in write path streams
Date Tue, 26 Sep 2017 01:04:00 GMT


Nate McCall updated CASSANDRA-13299:
    Component/s: Materialized Views

> Potential OOMs and lock contention in write path streams
> --------------------------------------------------------
>                 Key: CASSANDRA-13299
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Materialized Views
>            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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