Re: Should we warn against using too many partitions?

On 2019-Jun-06, David Rowley wrote:

> The attached patch is aimed at master. PG11 will need the planner
> memory and performance part tweaked and for PG10 I'll do that plus
> remove the mention of PRIMARY KEY and UNIQUE constraints on the
> partitioned table.

I think in PG10 something should be mentioned about PK and UNIQUE, so
that people doing their partitioning on that release can think ahead.
We don't want them to have to redesign and redo the whole setup when
upgrading to a newer release. If we had written the pg10 material back
when pg10 was fresh, it wouldn't make sense, but now that we know the
future, I don't see why we wouldn't do it. Maybe something like "The
current version does not support <this>, but future Postgres versions
do; consult their manuals for some limitations that may affect the
choice of partitioning strategy".

In the PG10 version you'll need to elide the mention of HASH
partitioning strategy.

Generally speaking, your material looks good to me. Also generally I +1
Justin's suggestions. The part that mentions a "relation cache entry"
seems too low-level as-is, though ... maybe just say it uses some memory
per partition without being too specific.

I think it'd be worthwhile to mention sub-partitioning.

I wonder if the PG10 manual should just suggest to skip to PG11 if
they're setting up partitioning for the first time.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services