[Postgres-xc-developers] Postgres-xc coordinator operation

[Manikandan S. <ma...@vt...>]

Hi,

I am a graduate student working on my research in parallel databases. I
would like to know how the postgres-xc coordinator works. I understand that
the datanodes run the query in parallel and the results are collected by
the coordinator which runs any more computation that is required or just
provides the output to the client that requested the query. I would like to
know whether the coordinator does this data collection from datanodes in a
sequential fashion?
For example, lets consider we want to run the query on table *table_x*
which is hash distributed among 10 datanodes,
*select count(*) from table_x;*
Each datanode will run the query and give their local counts and the
coordinator has to collect the individual counts and come up with the final
count before sending the output. Is the data collection process at the
coordinator done in a sequential fashion? I am actually looking to
introduce some kind of parallelism in this data collection if it is
sequential and do performance studies. Please clarify.

-- 
Thanks
Mani
Department of Computer Science
Virginia Tech