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Unhappy thoughts about pg_dump and objects inherited from template1

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Philip Warner <pjw(at)rhyme(dot)com(dot)au>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Unhappy thoughts about pg_dump and objects inherited from template1
Date: 2000-11-03 00:35:26
Message-ID: 5165.973211726@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
We've hacked up pg_dump so that it won't dump objects inherited from
template1.  Unfortunately I have realized there are a couple of serious
problems:

1. What if the inherited object is a table or a sequence?  Its state may
no longer be the same as it was in template1 (eg, a table may contain
more or different rows than it did when copied from template1).  It
seems a perfectly natural use of the template1 functionality to store,
say, a table definition in template1 and then add rows to it in
inherited databases --- that's exactly what the system does with
pg_proc, for example.

2. For that matter, even function definitions might change once we
support ALTER FUNCTION, which we surely will someday.  Or, template1
might contain data which was not present when some other database was
created.  In this case, reloading template1 first will not reproduce
the prior state of that database.

3. What if the OID counter wraps around?  I've been telling people
that's not a fatal scenario ... but it sure is if pg_dump silently omits
data on the basis of ordered OID comparisons.

A solution that would work for pg_dumpall is to dump all the user items
in each database and dump template1 *last*.  This won't help much for
piecemeal pg_dump and restore, however.

Thoughts?  At the moment I'm afraid that the functionality we have is
worse than the way prior versions behaved --- not least because anyone
who was putting user data in template1 has probably gotten used to the
prior behavior.  Maybe we should give up the whole idea of user data
in template1.

			regards, tom lane

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