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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12269) Faster write path
Date Fri, 22 Jul 2016 13:48:20 GMT

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Sylvain Lebresne commented on CASSANDRA-12269:
----------------------------------------------

I went very quickly over the patch out of curiosity, and have a few remarks (not at all a
thorough review, mostly nitpicks):
* We don't need {{clusteringTypes}} in {{CFMetadata}}. Not sure why {{SerializationHeader}}
has that {{typesOf}} method, but we can simply get the list of types through {{metadata.comparator.subtypes()}}.
* *Really* dislike making the fields public in {{Columns}} and {{BTreeRow}}. It's both leaking
abstraction and is imo dangerous. From a quick glance, it seems we can easily avoid both by
simply adding a {{apply(Function f)}} method to both {{Row}} and {{Columns}}.
* The reuse of {{SerializationHeader}} feels pretty ugly to me. Are we really gaining much
by saving the allocation of that one object (it's not like it's allocated for every cell we
read)?
* Using arrays for wrapping single ints for lambdas also doesn't feel too elegant to me. Would
prefer adding a very simple IntWrapper class with some {{add()}}/{{get()}} methods in utils.


> Faster write path
> -----------------
>
>                 Key: CASSANDRA-12269
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12269
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: T Jake Luciani
>            Assignee: T Jake Luciani
>             Fix For: 3.10
>
>
> The new storage engine (CASSANDRA-8099) has caused a regression in write performance.
 This ticket is to address it and bring 3.0 as close to 2.2 as possible. There are four main
reasons for this I've discovered after much toil:
> 1.  The cost of calculating the size of a serialized row is higher now since we no longer
have the cell name and value managed as ByteBuffers as we did pre-3.0.  That means we current
re-serialize the row twice, once to calculate the size and once to write the data.  This happens
during the SSTable writes and was addressed in CASSANDRA-9766.
>      Double serialization is also happening in CommitLog and the MessagingService.  We
need to apply the same techniques to these as we did to the SSTable serialization.
> 2.  Even after fixing (1) there is still an issue with there being more GC pressure and
CPU usage in 3.0 due to the fact that we encode everything from the {{Column}} to the {{Row}}
to the {{Partition}} as a {{BTree}}.  Specifically, the {{BTreeSearchIterator}} is used for
all iterator() methods.  Both these classes are useful for efficient removal and searching
of the trees but in the case of SerDe we almost always want to simply walk the entire tree
forwards or reversed and apply a function to each element.  To that end, we can use lambdas
and do this without any extra classes.
> 3.  We use a lot of thread locals and check them constantly on the read/write paths.
 For client warnings, tracing, temp buffers, etc.  We should move all thread locals to FastThreadLocals
and threads to FastThreadLocalThreads.
> 4.  We changed the memtable flusher defaults in 3.2 that caused a regression see: CASSANDRA-12228



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