Re: [PERFORM] Very poor read performance, query independent

I think the iowait > 12.5% is due to the parallel query execution.  But then the question is, why is it only 25% when you have 10 fold parallelism?

It certainly looks like you are doing more than 4MB/s there, so maybe something is wrong with the instrumentation, or how you are interpreting it.  

Although it is still less than perhaps it could do.  To put a baseline on what you can expect out of parallel seq scans, can you do something like:

explain (analyze, buffers) select avg(doctets) from flow;

Cheers,

Jeff