Re: keep a java program open

["David Morris" <David.Morris@xxxxxxxxxxxxx>]

Simon,

Thanks for the detailed explanation. In my case I still use the sorted
data
queue, but it only contains an offset and length for a user space
entry.
I think the main improvement comes from a user space being able to
store variable length entries more efficiently.

I don't know where you find this stuff, so I can't go look myself, but
if you
know off hand, I would be interested in whether the  the data queue
sorted on every dequeue or only on a dequeue with when after an
entry has arrived? Also, do you know whether the whole entry is sorted

rather than just the key? Maybe that is why I could not recognize a
difference between sorted data queues and a user index.

David Morris

>>> shc@flybynight.com.au 01/22/02 04:37PM >>>

Hello David,

You wrote:
>I always believed the manuals that said data queues were the fastest
>means of interprocess communication and were extremely lightweight.

They are fast -- faster than the alternatives of message queue or file
--
and user queues are faster still.  The major problem with data queues
occurs when they are keyed AND you fill them with data before starting
the
process that fetches the data (may also occur when entries arrive on
the
queue faster than the queue reader can process them).

The reason is simple.  On RISC AS/400 a keyed queue is not sorted when
entries are added (as happened on IMPI) but rather sorted when a
dequeue
operation is performed.  The sort is not very efficient (On**2 last
time I
looked) and I don't believe it has changed.

So changing from keyed to sequential as you did would certainly make
an
improvement but I would expect a major benefit only if you were filling
the
queue before processing the entries.

Regards,
Simon Coulter.

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