From: | Florian Pflug <fgp(at)phlo(dot)org> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Synchronized snapshots versus multiple databases |
Date: | 2011-10-21 18:06:13 |
Message-ID: | B3378081-46DD-4F6F-BF75-D129313F6AC0@phlo.org |
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Lists: | pgsql-hackers |
On Oct21, 2011, at 19:47 , Robert Haas wrote:
> On Fri, Oct 21, 2011 at 1:40 PM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
>> AFAIR, the performance hit we'd take by making the vacuum cutoff point
>> (i.e. GetOldestXmin()) global instead of database-local has been repeatedly
>> used in the past as an against against cross-database queries. I have to
>> admit that I currently cannot seem to find an entry in the archives to
>> back that up, though.
> I haven't seen anyone explain why they really need this feature
> anyway, and I think it's going in the wrong direction. IMHO, anyone
> who wants to be doing cross-database queries should be using schemas
> instead, and if that's not workable for some reason, then we should
> improve the schema implementation until it becomes workable. I think
> that the target use case for separate databases ought to be
> multi-tenancy, but what is needed there is actually more isolation
> (e.g. wrt/role names, cluster-wide visibility of pg_database contents,
> etc.), not less.
Agreed. I wasn't trying to argue for cross-database queries - quite the opposite,
actually. My point was more that since we've used database isolation as an
argument against cross-database queries in the past, we shouldn't sacrifice
it now for synchronized snapshots.
best regards,
Florian Pflug
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