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Re: WAL directory size calculation - Mailing list pgsql-general

From	David G. Johnston
Subject	Re: WAL directory size calculation
Date	July 28, 2016 13:33:32
Msg-id	CAKFQuwaMGb-qMnf0T0F35NQg_FidzVugnBYhSz3AybMwkwppOg@mail.gmail.com Whole thread Raw
In response to	WAL directory size calculation (Moreno Andreo <moreno.andreo@evolu-s.it>)
Responses	Re: WAL directory size calculation Re: WAL directory size calculation
List	pgsql-general

On Thu, Jul 28, 2016 at 9:25 AM, Moreno Andreo <moreno.andreo@evolu-s.it> wrote:

I've read somewhere that the formula should be 16 MB * 3 * checkpoint_segment in size.

[...]

Using the above formula I have:
16 MB * 3 * 1 GB
that leads to to ... uh .. 48000 TB?

You seem to be mis-remembering the formula.

checkpoiint_segments is a quantity (i.e., unit-less), not a size. Saying its "1GB" makes no sense.

I'm also doubting you multiply it by 3 - add three to it maybe...

Each segment takes 16MB. The total space required is that times whatever maximum count of segments you expect to have.

I'd suggest waiting for better responses on these lists or searching out prior conversations on this topic - of which I am sure there are many.

David J.

From: Moreno Andreo
Date: 28 July 2016, 13:25:15
Subject: WAL directory size calculation

From: Scott Marlowe
Date: 28 July 2016, 13:38:57
Subject: Re: Uber migrated from Postgres to MySQL