Examples of com.facebook.presto.jdbc.internal.netty.channel.FileRegion

com.facebook.presto.jdbc.internal.netty.channel.FileRegion

kipedia.org/wiki/Zero-copy">zero-copy file transfer.

Upgrade your JDK / JRE

{@link FileChannel#transferTo(long,long,WritableByteChannel)} has at leastfour known bugs in the old versions of Sun JDK and perhaps its derived ones. Please upgrade your JDK to 1.6.0_18 or later version if you are going to use zero-copy file transfer.

5103988 - FileChannel.transferTo() should return -1 for EAGAIN instead throws IOException
6253145 - FileChannel.transferTo() on Linux fails when going beyond 2GB boundary
6427312 - FileChannel.transferTo() throws IOException "system call interrupted"
6470086 - FileChannel.transferTo(2147483647, 1, channel) causes "Value too large" exception

Check your operating system and JDK / JRE

If your operating system (or JDK / JRE) does not support zero-copy file transfer, sending a file with {@link FileRegion} might fail or yield worseperformance. For example, sending a large file doesn't work well in Windows.

Not all transports support it

Currently, the NIO transport is the only transport that supports {@link FileRegion}. Attempting to write a {@link FileRegion} to non-NIO {@link Channel} will triggera {@link ClassCastException} or a similar exception.

            int length = 0;


            // Add support to write a FileRegion. This in fact will not give any performance gain
            // but at least it not fail and we did the best to emulate it
            if (message instanceof FileRegion) {
                FileRegion fr = (FileRegion) message;
                try {
                    synchronized (out) {
                        WritableByteChannel  bchannel = Channels.newChannel(out);


                        long i;
                        while ((i = fr.transferTo(bchannel, length)) > 0) {
                            length += i;
                            if (length >= fr.getCount()) {
                                break;
                            }
                        }
                    }
                } finally {
                    if (fr instanceof DefaultFileRegion) {
                        DefaultFileRegion dfr = (DefaultFileRegion) fr;
                        if (dfr.releaseAfterTransfer()) {
                            fr.releaseExternalResources();
                        }
                    }
                }
            } else {
                ChannelBuffer a = (ChannelBuffer) message;