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https://issues.apache.org/jira/browse/CASSANDRA-15389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17015387#comment-17015387
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Benedict Elliott Smith commented on CASSANDRA-15389:
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Great!
A couple of really minor things:
* I still see the Long.MIN_VALUE sentinel, maybe you forgot to push latest
commit?
* I don't think any caller of {{apply}} uses {{stopCondition}} anymore?
* In both {{apply}} and {{accumulate}}:
** We could test {{<= childOffset}} to avoid the slightly confusing maths to
calculate {{limit}}
** I have a very mild preference for keeping it to {{< childOffset}} and just
repeating the child logic, particularly since it's only a single line in each
case, as I find it makes it clearer we're visiting one more child, and it gives
the branch predictor less to do (though there's a good chance the compiler will
do it anyway, if we use {{<= childOffset}} in the guard)
Otherwise looks ready to me
> Minimize BTree iterator allocations
> -----------------------------------
>
> Key: CASSANDRA-15389
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15389
> Project: Cassandra
> Issue Type: Sub-task
> Components: Local/Compaction
> Reporter: Blake Eggleston
> Assignee: Blake Eggleston
> Priority: Normal
> Fix For: 4.0
>
>
> Allocations of BTree iterators contribute a lot amount of garbage to the
> compaction and read paths.
> This patch removes most btree iterator allocations on hot paths by:
> • using Row#apply where appropriate on frequently called methods
> (Row#digest, Row#validateData
> • adding BTree accumulate method. Like the apply method, this method walks
> the btree with a function that takes and returns a long argument, this
> eliminates iterator allocations without adding helper object allocations
> (BTreeRow#hasComplex, BTreeRow#hasInvalidDeletions, BTreeRow#dataSize,
> BTreeRow#unsharedHeapSizeExcludingData, Rows#collectStats,
> UnfilteredSerializer#serializedRowBodySize) as well as eliminating the
> allocation of helper objects in places where apply was used previously^[1]^.
> • Create map of columns in SerializationHeader, this lets us avoid
> allocating a btree search iterator for each row we serialize.
> These optimizations reduce garbage created during compaction by up to 13.5%
>
> [1] the memory test does measure memory allocated by lambdas capturing objects
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