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Subject: Re: [pgsql-admin] "Soft-hitting" the 1600 column limit
From: Scott Ribe <scott_ribe@elevated-dev.com>
In-Reply-To: 
 <CAKFQuwbuurPFxQ=ts2znAC-STpF9AW7C91qKXsGThWQr8u4Faw@mail.gmail.com>
Date: Wed, 6 Jun 2018 10:56:49 -0600
Cc: pgsql-admin <pgsql-admin@postgresql.org>,
 "David G. Johnston" <david.g.johnston@gmail.com>
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To: nunks <nunks.lol@gmail.com>
Precedence: bulk

David's answer is right. Basically every column added gets an index # =
which is not recycled.

I just want to add that a dump/restore will not bring in the history of =
deleted columns, thus resetting the column counter for the table.

--
Scott Ribe
scott_ribe@elevated-dev.com
https://www.linkedin.com/in/scottribe/


> On Jun 6, 2018, at 10:51 AM, David G. Johnston =
<david.g.johnston@gmail.com> wrote:
>=20
> On Wed, Jun 6, 2018 at 9:39 AM, nunks <nunks.lol@gmail.com> wrote:
> I reproduced this behavior in PostgreSQL 10.3 with a simple bash loop =
and a two-column table, one of which is fixed and the other is =
repeatedly dropped and re-created until the 1600 limit is reached.
>=20
> To me this is pretty cool, since I can use this limit as leverage to =
push the developers to the right path, but should Postgres be doing =
that? It's as if it doesn't decrement some counter when a column is =
dropped.
>=20
> =E2=80=8BThis is working as expected.  When dropping a column, or =
adding a new column that can contain nulls, PostgreSQL does not, and =
does not want to, rewrite the physically stored records/table.  Thus it =
must be capable of accepting records formed for prior table versions =
which means it must keep track of those now-deleted columns.=E2=80=8B
>=20
> I'm sure that there is more to it that requires reading, and =
understanding, the source code to comprehend; but that does seem to =
explain why its works the way it does.
>=20
> David J.
> =E2=80=8B