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Benjamin Roth commented on CASSANDRA-13299: ------------------------------------------- Relating to CASSANDRA-11670 this would also allow to write all streamed mutations to commitlog without problems. I also propose to do so with small streams (see CASSANDRA-13290). Writing small streams (e.g. < 100KB) to commitlog does not require a flush at the end of stream receive. This avoids tons of flushes if tons of tiny streams are sent during a repair session. These are maybe apples and oranges but fixing all these ends makes the whole process less error prone and probably perform better. > 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 > > 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 are processed. > 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. As > 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. -- This message was sent by Atlassian JIRA (v6.3.15#6346)