Re: pgsql: Rework the pg_statistic_ext catalog

On Sun, Jun 16, 2019 at 10:56:51AM +0200, Tomas Vondra wrote:
>On Sun, Jun 16, 2019 at 07:18:58AM +0100, Dean Rasheed wrote:
>>On Sun, 16 Jun 2019, 03:05 Tom Lane, <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>
>>>I wrote:
>>>> Tomas Vondra <tomas(dot)vondra(at)postgresql(dot)org> writes:
>>>>> Rework the pg_statistic_ext catalog
>>>
>>>> So ... not one of the buildfarm members that are running TAP tests
>>>> likes this. ...
>>>> I think probably what's happening is that pg_dump is still trying to dump
>>>> directly from the catalog, when what it needs to do now is dump from the
>>>> view, in case it's not running as superuser.
>>>
>>>I experimented with extracting the required data from the view, and
>>>there are at least two show-stopper problems:
>>>
>>>* The view doesn't expose pg_statistic_ext.oid, which pg_dump has to have
>>>for dependency tracking purposes. I think we could just add it though.
>>>Now that OIDs are ordinary columns it won't even look very odd.
>>>
>>>* Rather than just not exposing the critical data for stats you don't
>>>have privilege to read, the view doesn't expose anything at all.
>>>I do not think that's acceptable; it creates a significant hazard of
>>>data loss during pg_dump, for no very good reason. What we should
>>>be doing, IMO, is still showing all the rows but filling the data-value
>>>columns with nulls in rows where the caller can't access the underlying
>>>data.
>>>
>>>
>>
>>Hang on. Isn't the real problem that we should be revoking public access
>>from pg_statistic_ext_data, not pg_statistic_ext? Normal users should still
>>be able to see the stats definitions in the catalog table, but not the
>>stats data, so I think pg_dump wouldn't need changing.
>>
>
>Yeah, that's pretty much why we split the catalog - to allow pg_dump to
>read the definitions, without exposing the stats too. I'll look into
>this and push a fix to unbreak the buildfarm (sorry about that).
>

OK, the bug here seems to be pretty silly - the GRANT in system_views
does this:

GRANT SELECT (oid, stxrelid, stxname, stxnamespace, stxowner, stxkeys, stxkind)
ON pg_statistic_ext TO public;

but pg_dump also uses tableoid column. After adding it to the GRANT I
can run pg_dump using regular user just fine. I'll push this fix
shortly.

But we're not out of the woods yet, it seems. check-world still fails
for me with an error like this:

t/011_crash_recovery.pl .............. 1/3
# Failed test 'new xid after restart is greater'
# at t/011_crash_recovery.pl line 61.
# '486'
# >
# '486'

# Failed test 'xid is aborted after crash'
# at t/011_crash_recovery.pl line 65.
# got: 'committed'
# expected: 'aborted'
# Looks like you failed 2 tests of 3.
t/011_crash_recovery.pl .............. Dubious, test returned 2 (wstat 512, 0x200)
Failed 2/3 subtests

which I find rather strange. I have no idea why splitting a catalog and
adding a system view should affect recovery like this.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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