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https://issues.apache.org/jira/browse/CASSANDRA-15389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16987244#comment-16987244
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Blake Eggleston commented on CASSANDRA-15389:
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Just pushed up some changes addressing most of your comments.
*Rows#collectStats:* the overflow checks aren't actually doing anything, since
the longs are being shifted/masked to 32 bits. Force of habit when casing longs
to ints :). Addressed the other comments
*SerializationHeader:* fixed. Now using a single rewindable iterator, and added
a check to LeafBTreeSearchIterator to check the current position before doing a
binary search.
*BTreeRow* I had a bug in my {{hasComplexDeletion}} re-implementation that made
reverse iteration / stop condition seem unnecessary. We actually do need both
for hasComplexDeletion to work properly. Otherwise we’d only detect complex
deletion if it’s on the final complex column.
> 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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