Re: Unhappy thoughts about pg_dump and objects inherited from template1

Tom Lane wrote:
> 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.
   FWIW,  what  about having another "template0" database, where   nobody can add user data. Initially, template0 and
template1  are identically.  CREATE DATABASE get's a new switch (used by   the pg_dump output) that tells to create it
fromthe  vanilla   template0  DB  (generalized, so someone can setup a couple of   template<n>'s)  and  all  objects
inherited from  template1   (those not in template0) are regularly dumped per database.
 


Jan

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