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From: Sam Kidman <[email protected]>
To: Jeremy Smith <[email protected]>
Cc: [email protected]
Subject: Re: Poor performance after restoring database from snapshot on AWS RDS
Date: Thu, 6 Jun 2024 14:40:49 +1000
Message-ID: <CA+FDo=v7kUwMAMF61gr=gQS8S3oedpGooTuZiNgTTXt7oEyZzA@mail.gmail.com> (raw)
In-Reply-To: <CAM8SmLUMREu3MOSpfh58EoV9ysgWi8sFkbj_BnBJQjeJn3C+7Q@mail.gmail.com>
References: <CA+FDo=uz3+5vbQZDXN5SBAiZMnR0_w7YRZW+FS-VVuD3_XwB2g@mail.gmail.com>
	<CAM8SmLUMREu3MOSpfh58EoV9ysgWi8sFkbj_BnBJQjeJn3C+7Q@mail.gmail.com>

> 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 PM Jeremy Smith <[email protected]> wrote:
>
> On Wed, Jun 5, 2024 at 4:23 AM Sam Kidman <[email protected]> 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/USER_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

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