Re: Re: A separate table level option to control compression - Mailing list pgsql-hackers

From Pavan Deolasee
Subject Re: Re: A separate table level option to control compression
Date
Msg-id CABOikdMKWUk6v+rg2e_NmDPs-=CSvoq7jwMpG8TN3u3zim75KA@mail.gmail.com
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In response to Re: Re: A separate table level option to control compression  (Shaun Thomas <shaun.thomas@2ndquadrant.com>)
Responses Re: Re: A separate table level option to control compression
List pgsql-hackers
Hi,

On Thu, Mar 21, 2019 at 3:10 AM Shaun Thomas <shaun.thomas@2ndquadrant.com> wrote:

I can't really speak for the discussion related to `storage.sgml`, but
I based my investigation on the existing patch to `create_table.sgml`.
About the only thing I would suggest there is to possibly tweak the
wording.

* "The compress_tuple_target ... " for example should probably read
  "The toast_tuple_target parameter ...".
* "the (blocksize - header)" can drop "the".
* "If the value is set to a value" redundant wording should be rephrased;
  "If the specified value is greater than toast_tuple_target, then
  we will substitute the current setting of toast_tuple_target instead."
  would work.

Thanks Shaun. Attached patch makes these adjustments.
 
* I'd recommend a short discussion on what negative consequences can be
  expected by playing with this value. As an example in my tests, setting
  it very high may result in extremely sparse pages that could have an
  adverse impact on HOT updates.

Setting compress_tuple_target to a higher value won't be negative because the toast_tuple_target is used for compression anyways when  compress_tuple_target is higher than toast_tuple_target. May be some discussion in the paragraph related to toast_tuple_target can be added to explain the negative impact of the high value.

I added a small discussion about negative effects of setting  compress_tuple_target lower though, per your suggestion.

Also added some details in storage.sgml as recommended by Sawada-san. Hope this helps.

Thanks,
Pavan

--
 Pavan Deolasee                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services
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