Hi Reginald -
Very interesting question - no one has ever asked this...I'm curious why you're curious - would you mind filling me in why this would be useful information to you?
Now, to directly address your question: It's really hard to say. Just because we spin up a process doesn't mean that process is going to take an immediate and constant connection against postgresql (therefore spinning up another postgres.exe process).
And we don't really document how this works, as the behavior changes from version to version -- for example, in previous versions of Tableau Server, the lion's share of communication with the our metadata database (postgresql) went through the app server process. Now, in 7, the VizQL processes can and do also talk to it.
Hope this helps a little tiny bit?
Background: I have configured a cluster of 6 Tableau 7 Servers - 1 Primary and 5 Workers; I have also configured a failover sever in the event that the primary goes down.
What I am trying do: Creating a document that outlines what and how many Tableau processes should be running at any particular time e.g. If certain processes or if the number of processes falls below a certain threshold, then an alert will created and the Tableau Developer on call will be notified.
Obviously the counts I enter in the document have to be correct otherwise false positive alerts will be generated.
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Neat idea! Probably won't work with Postgre.exe, though.
Unlike a database like SQL Server, PostgreSQL isn't multi-threaded. It approaches the scalability question by spinning up a new process for each connection...then killing it when the connection is closed.
It's going to be nigh impossible for you to know how many of these you should expect to be up and running at any given time - because it all depends on load and what other Tableau processes happen to be doing that might cause a connection to PostgreSQL. You might rough-guess a "range" of postgres processes, but even that would raise false positives semi-regularly.
In your shoes, I probably leave postgres off the list of things to watch...
Thanks for the feedback. I decided to set a minimum threshold for the number of Postgre.exe processes that should be running at anyone time.
Hopefully I won't get too many false positives once our Tableau v7 Server cluster goes live.