franz1981 commented on a change in pull request #2522: ARTEMIS-2239 Zero-copy
NIO/MAPPED TimedBuffer
URL: https://github.com/apache/activemq-artemis/pull/2522#discussion_r251011676
##########
File path:
artemis-journal/src/main/java/org/apache/activemq/artemis/core/io/buffer/TimedBuffer.java
##########
@@ -358,13 +358,7 @@ public boolean flushBatch() {
bytesFlushed.addAndGet(pos);
}
- final ByteBuffer bufferToFlush =
bufferObserver.newBuffer(bufferSize, pos);
- //bufferObserver::newBuffer doesn't necessary return a buffer
with limit == pos or limit == bufferSize!!
- bufferToFlush.limit(pos);
- //perform memcpy under the hood due to the off heap buffer
- buffer.getBytes(0, bufferToFlush);
-
- bufferObserver.flushBuffer(bufferToFlush, pendingSync,
callbacks);
+ bufferObserver.flushBuffer(buffer.byteBuf(), pendingSync,
callbacks);
Review comment:
By default `AbstractSequentialFile` cannot say if the underline file is
performing async or sync writes, hence it will copy it, like it was done in the
past on `TimedBuffer`, while NIO/MAPPED can assume that writes are synchronous
and they will avoid the copy (if possilble; there are some contraints I've
written on the code).
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