Re: doc: explain pgstatindex fragmentation

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

To: Frédéric Yhuel <frederic.yhuel@dalibo.com>

Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Benoit Lobréau <benoit.lobreau@dalibo.com>

Date: 2025-01-22T11:34:23Z

Lists: pgsql-hackers

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doc: explain pgstatindex fragmentation
- 960135114629 19 (unreleased) landed

Hi,

On Tue, Nov 05, 2024 at 06:36:47PM +0100, Frédéric Yhuel wrote:
> Hi, I thought it would be nice to give the user a better idea of what
> avg_leaf_density and leaf_fragmentation mean.
> 
> Patch attached. What do you think?

Yeah, I think that can not hurt to give more details, thanks for the proposal!

A few comments:

=== 1

+     <literal>avg_leaf_density</literal> can be seen as the inverse of bloat,

I'm not sure it's good to describe something as the inverse of "something
else". See my proposal below.

=== 2

I’m not sure we need to add the extra details in a paragraph below the fields
description. What about changing the fields description?

Something concise enough like?

avg_leaf_density: shows how full leaf pages currently are (100 if full)
leaf_fragmentation: shows how much physical and logical ordering of leaf pages
differ (zero if they don't)

Also the comments made in [1], [2] and [3] are not linked to this main thread,
adding them for reference here (but better to keep the conversation going
by replying to this email).

[1]: https://www.postgresql.org/message-id/4c5dee3a-8381-4e0f-b882-d1bd950e8972%40dalibo.com
[2]: https://www.postgresql.org/message-id/c70fcc72-eed6-475b-81c8-508422299351%40dalibo.com
[3]: https://www.postgresql.org/message-id/e8a6db36-073e-4ca3-b38c-b42d7094cba8%40dalibo.com

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com