JProfiler Get rid of your performance problems and memory leaks! Modern Garbage Collection Tuning Java Performance Training Courses COURSES AVAILABLE NOW. We can provide training courses to handle all your Java performance needs Java Performance Tuning, 2nd ed The classic and most comprehensive book on tuning Java Java Performance Tuning Newsletter Your source of Java performance news. Subscribe now! Enter email: Training online Threading Essentials course JProfiler Get rid of your performance problems and memory leaks!

Java performance tuning tips relevent to using nio, the new I/O packages released from version 1.4. (Not including tips for regular expressions).

The following pages have their detailed tips extracted below

• Using nonblocking I/O and memory-mapped buffers in SDK 1.4.
• Using NIO
• NIO
• The java
• File Channels, StackTraceElements,

The following detailed tips have been extracted from the raw tips page

http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin.html
Using nonblocking I/O and memory-mapped buffers in SDK 1.4. (Page last updated September 2001, Added 2001-10-22, Author Michael T. Nygard, Publisher JavaWorld). Tips:

• Before SDK 1.4, servers had a number of performance problems: i/o could easily be blocked; garbage was easily generated when reading i/o; many threads are needed to scale the server.
• Many threads each blocked on i/o is an inefficient architecture in comparison to one thread blocked on many i/o calls (multiplexed i/o).
• Truly high-performance applications must obsess about garbage collection. The more garbage generated, the lower the application throughput.
• A Buffer (java.nio.*Buffer) is a reusable portion of memory. A MappedByteBuffer can map a portion of a file directly into memory.
• Direct Buffer objects can be read/written directly from Channels, but nondirect Buffer objects have a data copy performed for read/writes to i/o (and so are slower and may generate garbage). Convert nondirect Buffers to direct Buffers if they will be used more than once.
• Scatter/gather operations allow i/o to operate to and from several Buffers in one operation, for increased efficiency. Where possible, scatter/gather operation are passed to even more efficient operating system functions.
• Channels can be configured to operate blocking or non-blocking i/o.
• Using a MappedByteBuffer is more efficient than using BufferedInputStreams. The operating system can page into memory more efficiently than BufferedInputStream can do a block read.
• Use Selectors to multiplex i/o and avoid having to block multiple threads waiting on i/o.

http://www-106.ibm.com/developerworks/java/library/j-javaio/
Using NIO (Page last updated March 2002, Added 2002-03-25, Author Aruna Kalagnanam and Balu G., Publisher IBM). Tips:

• A server that caters to hundreds of clients simultaneously must be able to use I/O services concurrently. Prior to 1.4, an almost one-to-one ratio of threads to clients made servers written in Java susceptible to enormous thread overhead, resulting in both performance problems and lack of scalability.
• The Reactor design pattern demultiplexes events and dispatches them to registered object handlers. (The Observer pattern is similar, but handles only a single source of events where the Reactor pattern handles multiple event sources).
• [Articles covers the changes needed to use java.nio to make a server efficiently muliplex non-blocking I/O from SDK 1.4].

http://www.fawcette.com/javapro/2002_03/magazine/columns/proshop/default.asp
NIO (Page last updated Daniel F. Savarese, Added 2002-02-22, Author February 2002, Publisher JavaPro). Tips:

• GatheringByteChannel lets you to write a sequence of bytes from multiple buffers, and ScatteringByteChannel allows you to read a sequence of bytes into multiple buffers. Both let you minimize the number of system calls meade by combining operations that might otherwise require multiple system calls.
• Selector allows you to multiplex I/O channels, reducing the number of threads required for efficient concurrent I/O operations.
• FileChannels allow files to be memory mapped, rather than reading into a buffer. This can be more efficient. [But note that both operations bring the file into memory in different ways, so which is faster will be system and data dependent].

http://developer.java.sun.com/developer/technicalArticles/releases/nio/
The java.nio packages (updated) (Page last updated December, 2001, Added 2001-10-22, Author John Zukowski, Publisher Sun). Tips:

• Direct buffers have a higher creation cost than non-direct buffers because they use native system operations rather than JVM operations.
• Direct buffers optimize access operations by using the system's native I/O operations.
• Reduce threads by multiplexing I/O using selectors: The new I/O capabilities, allow you to create a Web server that does not require one thread per connection.

http://developer.java.sun.com/developer/JDCTechTips/2002/tt0507.html
File Channels, StackTraceElements, (Page last updated May 2002, Added 2002-05-19, Author Glen McCluskey, Publisher Sun). Tips:

• File Channels (from the 1.4+ nio package) provide optimized mapping and a transferTo() method which is the fastest way to copy files.