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From: Ron Johnson <[email protected]>
To: pgsql-generallists.postgresql.org <[email protected]>
Subject: Re: Poor performance after restoring database from snapshot on AWS RDS
Date: Fri, 7 Jun 2024 08:13:55 -0400
Message-ID: <CANzqJaDta4gnZdB86DzMuSB4vTrd568S-=QiYwozj9PCpd1Www@mail.gmail.com> (raw)
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On Fri, Jun 7, 2024 at 4:36 AM Sam Kidman <[email protected]> wrote:

> > 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)
>

https://www.postgresql.org/docs/14/pgprewarm.html

pg_prewarm is probably what you want.  Don't know if RDS Postgresql
supports it or not, though.


>
> 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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