Re: datistemplate of pg_database does not behave as per description in documentation

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От Magnus Hagander
Тема Re: datistemplate of pg_database does not behave as per description in documentation
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Msg-id CABUevEwOHzwSPnzXKk5dy3hQP9GOsd=b7s9cK1VwewywEYqBtA@mail.gmail.com
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Ответ на datistemplate of pg_database does not behave as per description in documentation  (Rajeev rastogi <rajeev.rastogi@huawei.com>)
Ответы Re: datistemplate of pg_database does not behave as per description in documentation  (Stephen Frost <sfrost@snowman.net>)
Re: datistemplate of pg_database does not behave as per description in documentation  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-hackers
On Thu, Mar 27, 2014 at 9:12 AM, Rajeev rastogi <rajeev.rastogi@huawei.com> wrote:

As per the documentation, datistemplate of pg_database is used in following way:

 

datistemplate

Bool

If true then this database can be used in the TEMPLATE clause of CREATE DATABASE to create a new database as a clone of this one

 

But current code does not behave in this manner.  Even if dbistemplate of database is false, still it allows to be used as template database.

 

postgres=# select datname, datistemplate from pg_database;

  datname  | datistemplate

-----------+---------------

template1 | t

template0 | t

postgres  | f

(3 rows)

 

postgres=# create database tempdb template postgres;              ---Actually this should fail.

CREATE DATABASE

 

Though I am not sure if we have to modify source code to align the behavior with documentation or we need to change the documentation itself.

To me it looks like code change will be better, so I am attaching the current patch with source code change.  After modification, result will be as follows:

 

postgres=# create database newtempdb template postgres;

ERROR:  DB name "postgres" given as template is not a template database

 

Please provide your feedback.



AFAICT, the *only* thing datistemplate is used is to set parameters in autovacuum.

So clearly we should do something. Changing the code that way carries the risk of breaking applications (or at least DBA scripts) for no apparent reason. I think it's better to document it.

However, that also raises a third option. We could just drop the idea if datistemplate completely, and remove the column. Since clearly it's not actually doing anything, and people seem to have been happy with that for a while, why do we need it in the first place? 


--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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