franz1981 edited a comment on issue #2844: ARTEMIS-1811 NIO Seq File should use RandomAccessFile with heap buffers URL: https://github.com/apache/activemq-artemis/pull/2844#issuecomment-533606931 @wy96f @clebertsuconic Just for completeness that's what would change: - [Java_java_io_RandomAccessFile_writeBytes->writeBytes](https://github.com/frohoff/jdk8u-jdk/blob/da0da73ab82ed714dc5be94acd2f0d00fbdfe2e9/src/share/native/java/io/RandomAccessFile.c#L85) - [writeBytes->IO_Write](https://github.com/frohoff/jdk8u-jdk/blob/da0da73ab82ed714dc5be94acd2f0d00fbdfe2e9/src/share/native/java/io/io_util.c#L189) by using a stack buffer if write/read length is <= `BUF_SIZE` (ie 8192 bytes) or with a fresh new buffer allocated using malloc/free: in both cases GetByteArrayRegion/SetByteArrayRegion are used to perform a copy from/to the provided java `byte[]` - [IO_Write === handleWrite](https://github.com/frohoff/jdk8u-jdk/blob/da0da73ab82ed714dc5be94acd2f0d00fbdfe2e9/src/solaris/native/java/io/io_util_md.h#L71) - [handleWrite->write](https://github.com/frohoff/jdk8u-jdk/blob/da0da73ab82ed714dc5be94acd2f0d00fbdfe2e9/src/solaris/native/java/io/io_util_md.c#L164) I see that this PR has few advantages vs https://github.com/apache/activemq-artemis/pull/2832: - it is simpler/less impactfull on artemis code base - although copies always happen, no leaks can happen I see that for small writes/reads the perf hit is not very high because copy java byte[]<->stack allocated native byte[] copy is cheap if compared to the cost of the write/read syscall and won't impact scalability of the native allocator, because malloc/free isn't used. I'm worried, because this change would enable a non-transparent handling of large writes/reads on JNI that could silently kill performance due to `malloc/free` + the large copy: that's exactly our use case for OpenWire and AMQP (until we'll get streaming of large messages in) and sadly it would affect CORE too, given that CORE writes/reads in 100KB sized chunks, that's > `BUF_SIZE` (ie 8192 bytes). PLEASE DO NOT MERGE: I would like to discuss with you about it :) I've added https://github.com/apache/activemq-artemis/pull/2844/commits/453c9796a486e6b9289e8cc8aa61e1ebcf41fd9f trying to mitigate the effects of it.
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