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:
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?
