From: Square Bob <square_bob@yahoo.com>
To: pgsql-general@lists.postgresql.org
Subject: amazon aroura config - seriously overcommited defaults? (May be Off Topic)
Date: Sat, 8 Dec 2018 12:00:33 -0700
Message-ID: <a053cc2d-bf74-cd33-09e1-024b7e87b494@yahoo.com> (raw)
All;
My apologies if this is off topic.
Our company is moving to Aurora, In the past I would take care not to
allow postgresql to over-commit memory beyond the actual memory on the
server, which meant I would add the buffer pool + (work_mem *
max_connections) + (maintenance_work_mem * autovacuum threads)
However as I look at the aroura defaults they are all off the charts,
for example, based on the calculations in the config (amazon doesn't
make it easy, some settings are in pages, some are in kb, some are who
knows what) I see the following settings as default in our aroura config:
The instance size is db.r4.xlarge
this instance size is listed as having 30.5GB of ram
Here's the default settings:
shared_buffers: {DBInstanceClassMemory/10922}
which equates to 24GB
work_mem: 64000 (kb)
which equates to 65.5MB
maintenance_work_mem: GREATEST({DBInstanceClassMemory/63963136*1024},65536)
which equates to 4.2GB
max_connections: LEAST({DBInstanceClassMemory/9531392},5000)
which equates to 3,380
According to my math (If I got it right) in a worst case scenario,
if we maxed out max_connections, work_mem and maintenance_work_mem limits
the db would request 247GB of memory
Additionally amazon has set effective_cache_size =
{DBInstanceClassMemory/10922}
which equates to about 2.9MB (which given the other outlandish setting
may be the only appropriate setting in the system)
What the hell is amazon doing here? Am I missing the boat on tuning
postgresql memory? Is amazon simply counting on the bet that users will
never fully utilize an instance?
Thanks in advance
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: square_bob@yahoo.com, pgsql-general@lists.postgresql.org
Subject: Re: amazon aroura config - seriously overcommited defaults? (May be Off Topic)
In-Reply-To: <a053cc2d-bf74-cd33-09e1-024b7e87b494@yahoo.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox