|From:||"Raja Agrawal" <raja(dot)agrawal(at)gmail(dot)com>|
|Subject:||Asynchronous I/O Support|
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Postgre8.1 doesn't seem to support asynchronous I/O. Has its design
been thought off already?
To tried doing with a simple example:
For a Index Nest loop join:
Fetch the outer tuples in an array, and then send all the
corresponding inner-tuple fetch requests asynchronously. Hence while
the IO is done for inner relation the new outer-tuple array can be
populated and other join operations can happen. This is maximum
overlap we could think of (doing minimal changes).
[The current implementation does sync IO, that is it fetches a outer
tuple, then requests corresponding inner tuple (waits till it gets),
does the processing, get another inner/outer tuple and so on.]
We have made appropriate changes in nodeNestloop.c but are unable to
track down how it issues the IO and gets the tuple in the slot.
Help! -- how to issue a async IO (given kernel 2.6 supports AIO), and
does a callback sceme or a sync IO on top of AIO, which of these will be best?
Also, as Graefe's paper suggests, a producer-consumer (thread-based)
is the best way to do this. But how to implement threading? (in case
its possible to?)
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