Re: PGSQL 9.3 - Materialized View - multithreading

On 04 Apr 2014, at 18:29, Nicolas Paris <niparisco@gmail.com> wrote:

> Hello,
>
> My question is about multiprocess and materialized View.
> http://www.postgresql.org/docs/9.3/static/sql-creatematerializedview.html
> I (will) have something like 3600 materialised views, and I would like to know the way to refresh them in a
multithreadway 
> (anderstand 8 cpu cores -> 8 refresh process  in the same time)

Hi Nick,

out of DB solution:

1. Produce a text file which contains the 3600 refresh commands you want to run in parallel. You can do that with
selectand format() if you don't have a list already.  

2. I'm going to simulate your 3600 'refresh' commands here with some select and sleep statements that finish at unknown
times.

(In BASH):
  for i in {1..3600} ; do echo "echo \"select pg_sleep(1+random()::int*10); select $i\" | psql mydb" ; done >
3600commands

3. Install Gnu Parallel     and type:

parallel < 3600commands

4. Parallel will automatically work out the appropriate number of cores/threads for your CPUs, or you can control it
manuallywith -j.  
It will also give you a live progress report if you use --progress.
e.g. this command balances 8 jobs at a time, prints a dynamic progress report and dumps stdout to /dev/null

parallel -j 8 --progress  < 3600commands > /dev/null

5. If you want to make debugging easier use the parameter --tag to tag output for each command.

Of course it would be much more elegant if someone implemented something like Gnu Parallel inside postgres or psql ...
:-)

Hope this helps & have a nice day,

Graeme.