Re: [Postgres-xc-general] Data Node Scan Performance

[Aaron J. <aja...@re...>]

Interesting,

So, I wonder why I am seeing query times that are more than the sum of the total times required to perform the process without the coordinator.  For example, let's say the query was 'SELECT 500 as Id, Foo, Bar from MyTable WHERE Id = 186' - I could perform this query at all 4 nodes and they would take no more than 10 seconds to run individually.  However, when performed against the coordinator, this same query takes 65 seconds.  That's more than the total aggregate of all data nodes.

Any thoughts - is it completely attributed to the coordinator?

 
________________________________________
From: amul sul [sul...@ya...]
Sent: Tuesday, April 29, 2014 12:23 AM
To: Aaron Jackson; pos...@li...
Subject: Re: [Postgres-xc-general] Data Node Scan Performance

>On Tuesday, 29 April 2014 10:38 AM, Aaron Jackson <aja...@re...> wrote:
> my question is, does the coordinator execute the data node scan serially
>or in parallel - and if it's serially,
>is there any thought around how to make it parallel?

IMO, scan on data happens independently i.e parallel, the scan result is collected at co-ordinator and returned to client.

Referring distributed table using other than distribution key(in your case it Q instead of k), has little penalty.

Regards,
Amul Sul