It's true that HDFS (and Hadoop generally) doesn't currently have a ByteBuffer-based pread API. There is a JIRA open for this issue, HDFS-3246.
I do not know if implementing a ByteBuffer API for pread would be as big of a performance gain as implementing it for regular read. One issue is that when you do a pread, you always destroy the old BlockReader object and create a new one. This overhead may tend to make the overhead of doing a single buffer copy less significant in terms of total cost. I suppose it partly depends on how big the buffer is that is being copied... a really large pread would certainly benefit from avoiding the copy into a byte array. cheers, Colin On Tue, Dec 31, 2013 at 1:01 AM, lei liu <liulei...@gmail.com> wrote: > There is ByteBuffer read API for sequential read in CDH4.3.1, > example:public synchronized int read(final ByteBuffer buf) throws > IOException API. But there is not ByteBuffe read API for pread. > > Why don't support ByteBuffer read API for pread in CDH4.3.1? > > Thanks, > > LiuLei
