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From Dave Birdsall <>
Subject RE: investigating parallel scanner
Date Tue, 22 Mar 2016 23:26:21 GMT
Hi Eric,

Yes, that is true.

The Optimizer sometimes takes advantage of the MDAM ordering (that is, an
operator that consumes the rows produced by an MDAM scan may rely on the
order). So you'd need a flag in the scan node to know if this is true.

Actually, we may want to change the costing code in the Optimizer to take
into account the tradeoff of order + serial behavior vs. unordered + higher


-----Original Message-----
From: Eric Owhadi []
Sent: Tuesday, March 22, 2016 4:13 PM
Subject: RE: investigating parallel scanner

MDAM ordering is important for the sequencing of probes.
The resulting scan are not feeding the "next probe", so in theory, if the
probes where generating a list of scans to serve, this list could be
processed in random order, in parallel, if the parent node is not expecting
to receive data in order.
Anyway, MDAM scan optimization would have been a different beast, for now I
want to do a V1 that is not dealing with MDAM.

-----Original Message-----
From: Dave Birdsall []
Sent: Tuesday, March 22, 2016 6:08 PM
Subject: RE: investigating parallel scanner


I don't know about a flag.

MDAM, however, does assume that it is scanning things in order, so if MDAM
is present that's a clue.


-----Original Message-----
From: Eric Owhadi []
Sent: Tuesday, March 22, 2016 3:41 PM
Subject: investigating parallel scanner

Hello Trafodioneers,

In order to implement a parallel scanner, that would scan regions of a table
in parallel, but consequently will not return the rows in order, I was
hunting for a flag somewhere, I would have guessed in ComTdbHbaseAccess,
that would tell me if the return order is important or not on a scan
operator, so that I know if parallel scanner is a candidate, or if it is

But so far, have not been able to locate such a flag.

Any idea if it exist, and if yes where is it?

Thanks in advance for the help,


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