Aurora doesn’t use a typical file system so the RAM usually reserved for the OS
file system bufffer cache is instead used for shared_buffers.
We run multiple Aurora/ PG instances and they work quite well. There are
limitations in superuser private, so be aware of that, but generally speaking
Aurora/PG works well.
Bob Lunney
Sent from my PDP11
> On Dec 8, 2018, at 2:03 PM, Square Bob <square_...@yahoo.com> wrote:
>
> This question is probably more of a fit for the performance list, sorry for
> the cross post
>
>
>
> -------- Forwarded Message --------
> Subject: amazon aroura config - seriously overcommited defaults? (May be
> Off Topic)
> Date: Sat, 8 Dec 2018 12:00:33 -0700
> From: Square Bob <square_...@yahoo.com>
> To: pgsql-gene...@lists.postgresql.org
>
>
> 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
>
>
>
