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https://issues.apache.org/jira/browse/NET-550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14571789#comment-14571789
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Sebb commented on NET-550:
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The default is currently 1024. Is that really very inefficient?
> Default FTPClient bufferSize results in very slow retrieve transfers
> --------------------------------------------------------------------
>
> Key: NET-550
> URL: https://issues.apache.org/jira/browse/NET-550
> Project: Commons Net
> Issue Type: Bug
> Affects Versions: 3.3
> Reporter: Geoffrey Hardy
> Fix For: 3.4
>
> Attachments: net-buffercopy-ext.patch, net-buffercopy.patch
>
>
> While experimenting with FTPClient, I discovered that if I don't call
> setBufferSize(), the default value is zero. This results in retrieveFile()
> calling the version of InputStream.read() with no parameters, reading one
> byte at a time. For comparison, the downloading a CD ISO image of about
> ~648MB took 18m10s with the default settings. In contrast, calling
> setBufferSize(8192) took only 7.9s, an improvement of ~137x.
> Here is some sample code:
> {code:java}
> FTPClient ftp = new FTPClient();
> // ftp.setBufferSize(8192);
> ftp.setControlKeepAliveTimeout(300);
> ftp.setCopyStreamListener(new CopyStreamListener() {
> @Override
> public void bytesTransferred(long totalBytesTransferred, int
> bytesTransferred, long streamSize) {
> System.out.println("totalBytesTransferred: " + totalBytesTransferred
> + ", bytesTransferred: " + bytesTransferred + ", streamSize: " +
> streamSize);
> }
> @Override public void bytesTransferred(CopyStreamEvent event) {}
> });
> ftp.connect(host);
> ftp.login(user, pass);
> ftp.retrieveFile(file, outputStream);
> {code}
> The log message from the stream listener printed lots messages
> "bytesTransferred: 1" and totalBytesTransferred incremented by 1 each time.
> This corresponds to the part of the code which reads one byte at a time with
> {{int inputStream.read()}}.
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