[Postgres-xc-general] Performance when adding new datanode

[Bartłomiej W. <bar...@tu...>]

Hello,

Today I am testing the following simple cluster:    Host1(vm1, IP1, 
6cores 4GB ram, disk storage(very large throughput  ~Gbit/s)):    1 
gtm    +    1 coordinator    +    (1,2,3) datanode

Loading the database 100000 inserts and I received the time:       3m1s 
and    2m57s     (2 of 6 cores work mainly) -    100% of the data at 
each datanode (checked)
Then I do simple selects on that data and I received the time:      
28m29s  and  28m25s    (2 of 6 cores work mainly)

I refresh the database (drop and create database)
Then I add second datanode to the cluster, do the same test(inserts, 
selects) and I received:

2m59s    and  2m57s  (inserts)    (2 of 6 cores work mainly) - 50% of 
the data at each datanode (checked)
15m2s  and  13m41s  (selects)    (2 of 6 cores work mainly)

I refresh the database (drop and create database again)
Then I add third datanode and I received:

3m1s    and    2m58  (inserts)    (2 of 6 cores work mainly)    - 33% of 
the data at each datanode (checked)
9m35s  and  10m5s (selects)    (2 of 6 cores work mainly)


Is this results ok ? Why did not increase write performance(inserts) 
after adding a datanode? Why did not benefit more from other cores ?


The results are reproducible (as you can see)


Regards!

BW