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https://issues.apache.org/jira/browse/CASSJAVA-60?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17904037#comment-17904037
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Jane He commented on CASSJAVA-60:
---------------------------------
Hi Tatu! Thank you for reporting this issue. I wonder which version of the Java
driver you are looking at?
I took a look at the current master branch:
[here|https://github.com/apache/cassandra-java-driver/blob/a322ca265654605123f4d7b889ad736c114f0c7e/core/src/main/java/com/datastax/oss/driver/internal/core/type/codec/VectorCodec.java#L66-L107].
It seems to me that it first holds all the individual element's `ByteBuffer`
in `ByteBuffer[] valueBuffs`, and then paste them one by one to `ByteBuffer
rv`. So, it seems to me that it approximately uses 2 * the memory size of the
return value `rv`. Is this what you refer to?
> Improve encoding performance of `CqlVector` by avoiding allocation of large
> number of temp `ByteBuffer`s
> --------------------------------------------------------------------------------------------------------
>
> Key: CASSJAVA-60
> URL: https://issues.apache.org/jira/browse/CASSJAVA-60
> Project: Apache Cassandra Java driver
> Issue Type: Improvement
> Components: Core
> Reporter: Tatu Saloranta
> Priority: Normal
>
> When profiling service that uses Cassandra Java Driver, inserting rows with
> Vector columns, I noticed that a significant source of generated garbage (and
> cpu usage) was due to encoding of `CqlVector` (which is essentially thin
> wrapper around `List<Float>`).
> A major reason is that value is encoded using delegation so that every
> individual vector element is encoded separately into throw-away `ByteBuffer`
> and only appended along with others in the end to get to actual full value.
> It should be possible to instead directly encode element values into fully
> allocated target buffer (as element count & per-element size are known). And
> possibly even just remove use of delegation if and when it is known that
> elements are always `Float`s.
>
>
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