cadonna commented on a change in pull request #10798:
URL: https://github.com/apache/kafka/pull/10798#discussion_r644566174
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File path:
streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBStore.java
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@@ -505,6 +506,14 @@ private void closeOpenIterators() {
}
}
+ private ByteBuffer createDirectByteBufferAndPut(byte[] bytes) {
+ ByteBuffer directBuffer = ByteBuffer.allocateDirect(bytes.length);
Review comment:
The
[javadocs](https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html)
say
> The buffers returned by this method typically have somewhat higher
allocation and deallocation costs than non-direct buffers.
So it seems allocating a direct buffer during each put might decrease
performance. The internal benchmarks we run on this PR did not show any
increase in throughput, but rather a decrease. However, I do not think the
decrease was significant, so the cause could also just be a bad day of the
environment. Anyways, continuously allocating a direct buffer does not seem to
be a good idea, as the javadocs also say:
> It is therefore recommended that direct buffers be allocated primarily for
large, long-lived buffers that are subject to the underlying system's native
I/O operations. In general it is best to allocate direct buffers only when they
yield a measureable gain in program performance.
Another thing to consider:
> The contents of direct buffers may reside outside of the normal
garbage-collected heap, and so their impact upon the memory footprint of an
application might not be obvious.
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