To: pgsql-performance@postgresql.org
From: Moreno Andreo <moreno.andreo@evolu-s.it>
Subject: Architectural question
Message-ID: <56BCCDB2.8050407@evolu-s.it>
Date: Thu, 11 Feb 2016 19:06:42 +0100
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Hi everyone,
     I have a question that I hope fits in this discussion group.

I'm migrating my actual server into a new, more powerful architecture on 
Google Cloud Platform.
ATM the server is a VM with 4 vCPUs (the host has 4 Xeon E2xx 3,1 GHZ, 
if I remember) and 32 GB RAM, just running Ubuntu Server 12.04 and 
PostgreSQL 9.1
The server contains about 350 DBs and the same number of roles (every 
role has its own database). Databases are made of about 75 tables that 
can contain blobs (one table is peculiar in containing blobs) and single 
blob size can grow up to 20-25 megabytes. ATM our biggest DB is about 30 
GB, 95% made of blobs.

Apart from user growth, that means more resource consumption, we are 
starting new services, that will have more and more impact on databases.
I read about how blobs are SLOW and I'm a bit worried on how to manage them.

Now, the actual question, is:
Having a VM that can be upgraded with a click on a panel and a reboot, 
and that the server fault is only related to a OS failure, should I keep 
a single-server solution (but I fear that I/O throughput will become 
even more inadequate) or is it convenient to migrate in a 2-server 
system? And, in case of 2-server configuration, what would you recommend?

Scenario 1:
Given 350 databases, I split them in 2, 175 on server 1 and 175 on 
server 2, having pgBouncer to resolve the connections and each server 
has its own workload

Scenario 2:
Server 1 -> Master, Server 2 -> Slave (Replicated with Slony or...?), 
Server 1 for writes, Server 2 for reads

Last thing: should blobs (or the whole database directory itself) go in 
a different partition, to optimize performance, or in VM environment 
this is not a concern anymore?

I tried to be as brief as possible, if you need some more details.... 
just ask :-)

Thanks in advance,
Moreno.


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