Re: cataloguing NOT NULL constraints

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: cataloguing NOT NULL constraints
Date: 2023-06-30 11:44:03
Message-ID: 20230630114403.nru7f6i5ejgcxz42@alvherre.pgsql
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OK, so here's a new attempt to get this working correctly. This time I
did try the new pg_upgrade when starting with a pg_dumpall produced by a
server in branch 14 after running the regression tests. The pg_upgrade
support is *really* finicky ...

The main novelty in this version of the patch, is that we now emit
"throwaway" NOT NULL constraints when a column is part of the primary
key. Then, after the PK is created, we run a DROP for that constraint.
That lets us create the PK without having to scan the table during
pg_upgrade. (I thought about adding a new dump object, either one per
table or just a single one for the whole dump, which would carry the
ALTER TABLE .. DROP CONSTRAINT commands for those throwaway constraints.
I decided that this is unnecessary, so the code the command in the same
dump object that does ALTER TABLE ADD PRIMARY KEY seems good enough. If
somebody sees a reason to do it differently, we can.)

There's new funny business with RelationGetIndexList and primary keys of
partitioned tables. With the patch, we continue to store the OID of the
PK even when that index is marked invalid. The reason for this is
pg_dump: when it does the ALTER TABLE to drop the NOT NULLs, the columns
would become marked nullable, because since the PK is invalid, it's not
considered to protect the columns. I guess it might be possible to
implement this in some other way, but I found none that were reasonable.
I didn't find that did had any undesirable side-effects anyway.

Scanning this thread, I think I left one reported issue unfixed related
to tables created LIKE others. I'll give it a look later. Other than
that I think all bases are covered, but I intend to leave the patch open
until near the end of the CF, in case someone wants to play with it.

Álvaro Herrera Breisgau, Deutschland —
"It takes less than 2 seconds to get to 78% complete; that's a good sign.
A few seconds later it's at 90%, but it seems to have stuck there. Did
somebody make percentages logarithmic while I wasn't looking?"

Attachment Content-Type Size
v9-0001-Add-pg_constraint-rows-for-NOT-NULL-constraints.patch text/x-diff 215.6 KB

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