Direct I/O

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Tony Hannan - 23 Jan 2006 16:11 GMT

Hello all,

Do the direct buffers in the java.nio package have the same effect as
using the open function with the O_DIRECT flag in Linux?

I am the TA for a database implementations class and we want to access
disk directly and do our own buffering. We are treating a single OS file
like a disk partition.

Thanks,
Tony

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John C. Bollinger - 24 Jan 2006 03:49 GMT

> Hello all,
>
> Do the direct buffers in the java.nio package have the same effect as
> using the open function with the O_DIRECT flag in Linux?

I can't tell for sure from the docs, which means that you cannot rely on
it being so. The two sound similar, but it is not clear whether an NIO
direct buffer bypasses only Java-side caching or both Java and native
caching.

> I am the TA for a database implementations class and we want to access
> disk directly and do our own buffering. We are treating a single OS file
> like a disk partition.

I know of nothing more likely to get what you ask in Java than a direct
ByteBuffer, as you suggested. If you are not already aware of it, then
you should also look at method FileChannel.force() as a complement /
failsafe.

Sorry I can't be more definite.

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John Bollinger
jobollin@indiana.edu

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