[Info-ingres] 4k Cache

[Michael Leo]

Roy,

I had to look up "abstemious" ...


Michael Leo

Kettle River Consulting Inc

612-859-2108

mleo at kettleriverconsulting.com

________________________________
From: info-ingres-bounces at lists.planetingres.org <info-ingres-bounces at lists.planetingres.org> on behalf of Roy Hann <specially at processed.almost.meat>
Sent: Thursday, September 9, 2021 9:44 AM
To: info-ingres at lists.planetingres.org <info-ingres at lists.planetingres.org>
Subject: Re: [Info-ingres] 4k Cache

Steve wrote:

> God willing, as mentioned above, I plan to increase the page size of
> all user tables and indexes to 8k and 4k, respectively. Currently both
> are 2k. This was a recommendation by Actian.
>
> A small portion of the tables are already 8k; that being the default
> page size.
>
> Upon making these changes, I was thinking of reducing the 2k buffer cache
> by 75%, as the only 2k tables at that point would be the system catalogs
> (I think they’re 2k) and possibly the odd users’ own private tables. I
> figured the memory saved could be reallocated to the 8k cache. Is that
> a reasonable idea?

It's not unreasonable, but generally I think Ingres is abstemious
to a fault with DMF memory. Freeing up what is probably only a very
small amount of memory won't make much difference.

I am not the world's biggest fan of 4k pages. Owing to the larger
per-row overhead of "large" pages you might find you waste less disk
space if you just use 8k pages for everything.

You don't mention what you are expecting to get from larger page sizes.
They do enable ALTER TABLE which is handy, but if you are
using locking (and you will be) rather than MVCC you might find page
sizes bigger than 2k aggravate any lock-contention you may have.

Please let us know how you get on.

Roy

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