marking tuples

<div style="text-align: left;">Hi,<br />I am implementing a new algorithm inside postgresql for a side research
project.I am just wondering if anyone may give me few hints about the following problem:<br /><br />Consider the
followingplan:<br /><br />NewAggregate<br />    ->NewJoin<br />          ->NewJoin<br />               
->NewJoin<br/>                       ->SeqScan<br />                        ->SeqScan<br />               
->SeqScan<br/>          ->SeqScan<br /><br /><br />In my algorithm, <br />each NewJoin node may "mark" its
ps_ResultTupleSlotwith either red/green. I need that mark to flow in the pipeline so that i can collect them at the top
aggregate.<br/><br />Any hints about how to keep such mark is greatly appreciated.<br /><br />Thanks a lot,<br
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