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` (=== 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 while providing this change it 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 :)

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