Thread: Re: [HACKERS] [COMMITTERS] pgsql: Add pg_sequence system catalog

Peter,

* Peter Eisentraut (peter_e@gmx.net) wrote:
> Add pg_sequence system catalog

The query this added to dumpSequence() seems to think that sequence
names are unique across databases:

appendPQExpBuffer(query,                 "SELECT seqstart, seqincrement, "                 "CASE WHEN seqincrement > 0
ANDseqmax = %s THEN NULL "                 "     WHEN seqincrement < 0 AND seqmax = -1 THEN NULL "                 "
ELSE seqmax "                 "END AS seqmax, "                 "CASE WHEN seqincrement > 0 AND seqmin = 1 THEN NULL "
              "     WHEN seqincrement < 0 AND seqmin = %s THEN NULL "                 "     ELSE seqmin "
 "END AS seqmin, "                 "seqcache, seqcycle "                 "FROM pg_class c "                 "JOIN
pg_sequences ON (s.seqrelid = c.oid) "                 "WHERE relname = ",                 bufx, bufm);
 
appendStringLiteralAH(query, tbinfo->dobj.name, fout);

Note that tbinfo->dobj.name contains just the name, and trying to match
based on just 'relname' isn't going to work since sequences with the
same name can exist in difference schemas.

I'd suggest using our usual approach in pg_dump, which is matching based
on the OID, like so:

WHERE c.oid = '%u'::oid

The OID is in: tbinfo->dobj.catId.oid

Also, you should move the selectSourceSchema() into the per-version
branches and set it to 'pg_catalog' for PG10 and up, which would allow
you to avoid having to qualify the table names, et al.  As is, this
query will also fail if a user has created a 'pg_class' or
'pg_sequence' table in their schema.

Thanks!

Stephen

Peter, all,

* Stephen Frost (sfrost@snowman.net) wrote:
> * Peter Eisentraut (peter_e@gmx.net) wrote:
> > Add pg_sequence system catalog
>
> The query this added to dumpSequence() seems to think that sequence
> names are unique across databases:

Just FYI, I've added this to the PG10 open items list so it doesn't get
forgotten (and so I can swap it out of my head and into a wiki):

https://wiki.postgresql.org/wiki/PostgreSQL_10_Open_Items

Thanks!

Stephen

On 1/19/17 11:03 AM, Stephen Frost wrote:
> I'd suggest using our usual approach in pg_dump, which is matching based
> on the OID, like so:
> 
> WHERE c.oid = '%u'::oid
> 
> The OID is in: tbinfo->dobj.catId.oid
> 
> Also, you should move the selectSourceSchema() into the per-version
> branches and set it to 'pg_catalog' for PG10 and up, which would allow
> you to avoid having to qualify the table names, et al.

Does the attached patch look correct to you?

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Peter,

* Peter Eisentraut (peter.eisentraut@2ndquadrant.com) wrote:
> On 1/19/17 11:03 AM, Stephen Frost wrote:
> > I'd suggest using our usual approach in pg_dump, which is matching based
> > on the OID, like so:
> >
> > WHERE c.oid = '%u'::oid
> >
> > The OID is in: tbinfo->dobj.catId.oid
> >
> > Also, you should move the selectSourceSchema() into the per-version
> > branches and set it to 'pg_catalog' for PG10 and up, which would allow
> > you to avoid having to qualify the table names, et al.
>
> Does the attached patch look correct to you?

On a one-over, yes, that looks correct and avoids the issue of running
in a user's schema.

It wouldn't hurt to add a comment as to why things are so different in
PG10 than other versions, ie:

/** In PG10, sequence meta-data was moved into pg_sequence, so switch to* the pg_catalog schema instead of operating in
auser schema and pull* the necessary meta-data from there.*/ 

Thanks!

Stephen

On 1/24/17 10:23 AM, Stephen Frost wrote:
> It wouldn't hurt to add a comment as to why things are so different in
> PG10 than other versions, ie:
> 
> /*
>  * In PG10, sequence meta-data was moved into pg_sequence, so switch to
>  * the pg_catalog schema instead of operating in a user schema and pull
>  * the necessary meta-data from there.
>  */

I've committed this, but I've put the comment in the old sections and
explained how they are different from the new style, instead of vice versa.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services