Subject: Precompressed data in TOASTed columns (was Re: Regarding postgreSQL
 performance on DRAM)
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From: Ron <ronljohnsonjr@gmail.com>
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Date: Wed, 20 Feb 2019 18:38:20 -0600
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On 2/20/19 3:04 PM, Tom Lane wrote:
[snip]
> Well, the entire tuple would be 25600 bytes plus some overhead, which
> cannot fit on a Postgres page (8K, unless the OP changed compile options
> without mentioning it).  So something has to be done to make it fit, and
> that something is going to be toasting any fields that can be toasted.
>
>  From memory, our threshold for trying to make tuples narrower is only
> a quarter-page anyway, so that the toaster will be trying to get this
> down to 2K if it can.  That's certainly going to involve compressing
> every field, and I wouldn't be surprised if a lot of them get shoved
> out-of-line too.
>
> The OP might care to read
>
> https://www.postgresql.org/docs/current/storage-toast.html

Based on that and https://www.postgresql.org/docs/9.6/sql-altertable.html 
should I think about doing a SET STORAGE=EXTERNAL on columns with PDF and 
compressed TIFF data?

Thanks

-- 
Angular momentum makes the world go 'round.