Re: Add relcreated (timestamp) column to pg_class catalog to record the time an object was created

On 04/20/2016 04:09 PM, Melvin Davidson wrote:
>
> On Wed, Apr 20, 2016 at 6:17 PM, Kevin Grittner <kgrittn@gmail.com
> <mailto:kgrittn@gmail.com>> wrote:
>
>     On Wed, Apr 20, 2016 at 4:40 PM, Melvin Davidson
>     <melvin6925@gmail.com <mailto:melvin6925@gmail.com>> wrote:
>
>     > As for what I want from the community, I would like other users
>     > and dba's to weigh in on this request and it's usefulness.
>
>     When I was a DBA on a team responsible for hundreds of
>     geographically distributed databases, initially using products with
>     this feature and then moving to PostgreSQL, I occasionally found
>     this feature to be a minor convenience when it was present.  We
>     kept the DDL for recreating everything under source control, and
>     each new release contained the DDL to move from one state to the
>     next, so such a column didn't give us anything we couldn't get by
>     consulting the "official" DDL.  But, as an example of where it
>     could save a few minutes, if someone had been allowed to run ad hoc
>     reports or data cleanup on a database it was a quick way to look
>     for stray tables they may have generated to keep intermediate
>     results or exceptions, so we could follow up on disposition of
>     those tables.
>
>     It would take a lot of such incidents to add up to enough time to
>     add this as a proper feature, which is probably why nobody with
>     resources to devote to adding features has prioritized it to the
>     point of developing a proposed patch.  That and the fact that there
>     is no guarantee that the community as a whole would feel that the
>     feature "carried its own weight" in terms of benefit / maintenance
>     cost, so it might not make it in anyway.
>
>     --
>     Kevin Grittner
>     EDB: http://www.enterprisedb.com
>     The Enterprise PostgreSQL Company
>
>
> Adrian,
> To answer your questions:
> "The first time an object was ever created?"
> Yes, AFAIK, objects in pg_class can only be "created" once, so
> relcreatedat would be the timestamp it
> is initially created. Otherwise, if an object is dropped and
> subsequently re-created, then by definition the relcreatedat must again
> populated.
>
> "The time it was created in a new database during a
> dump-restore/pg_upgrade/replication?"
> Yes  for new database, but no for upgrade/replication as by definition,
> the objects would already exist..

Not until pg_upgrade is done or replication is started, in either case a
new cluster is started probably at a different time from the original
cluster. To some people that would indicate they are actually dealing
with a different object. Again the problem is not the simple case, but
the complex one. The use case may start out as you state, but once it
was in the wild, you can rest assured folks will want more.

>
> Second thing:
>
> "pg_class does not track all the objects in a database, so what other
> system catalogs should be included. With the same questions as above."
> I am only concerned with the objects in pg_class as id'd by relkind. IE:
> tables, indexes, sequences, etc.

Again, that is your wish and is fairly simple. Now I usually do not make
guarantees, but in this case I will. If pg_class gets an object creation
time, the clamor will start immediately for the same thing to be done to
the other relevant system catalogs.

>
> Kevin,
> Thank you for your additional feedback. adhoc user temp tables is just
> one case.
> There is also the situation of tables with limitited use. EG:
> history_yyyymm, in which case it would facilitate dropping of tables
> that are no longer needed after x amount of time.
>
> --
> *Melvin Davidson*
> I reserve the right to fantasize.  Whether or not you
> wish to share my fantasy is entirely up to you.


--
Adrian Klaver
adrian.klaver@aklaver.com