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From: Sam Kidman <sam@fresho.com>
Date: Thu, 6 Jun 2024 14:40:49 +1000
Message-ID: <CA+FDo=v7kUwMAMF61gr=gQS8S3oedpGooTuZiNgTTXt7oEyZzA@mail.gmail.com>
Subject: Re: Poor performance after restoring database from snapshot on AWS RDS
To: Jeremy Smith <jeremy@musicsmith.net>
Cc: pgsql-general@lists.postgresql.org
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> This is due to the way that RDS restores snapshots.

Thanks, I never would have guessed. Would vacuum analyze be sufficient
to defeat the lazy loading or would we need to do something more
specific to our application? (for example. select(*) on some commonly
used tables)

I think vacuum full would certainly defeat the lazy loading since it
would copy all of the table data, but that may take a very long time
to run. I think vacuum analyze only scans a subset of rows but I might
be wrong about that.

Best, Sam

On Wed, Jun 5, 2024 at 10:09=E2=80=AFPM Jeremy Smith <jeremy@musicsmith.net=
> wrote:
>
> On Wed, Jun 5, 2024 at 4:23=E2=80=AFAM Sam Kidman <sam@fresho.com> wrote:
>
> > We get very poor performance in the staging environment after this
> > restore takes place - after some usage it seems to get better perhaps
> > because of caching.
> >
>
> This is due to the way that RDS restores snapshots.
>
> From the docs (https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USE=
R_RestoreFromSnapshot.html):
>
> You can use the restored DB instance as soon as its status is
> available. The DB instance continues to load data in the background.
> This is known as lazy loading.
>
> If you access data that hasn't been loaded yet, the DB instance
> immediately downloads the requested data from Amazon S3, and then
> continues loading the rest of the data in the background.
>
>
>
>   -Jeremy