Re: default_text_search_config and expression indexes

On Fri, 27 Jul 2007, Bruce Momjian wrote:

> Magnus Hagander wrote:
>>> However, the big problem is that the expressions used in expression
>>> indexes should not change their output based on the value of a GUC
>>> variable (because it would corrupt the index), but in the case above,
>>> default_text_search_config controls what configuration is used, and
>>> hence the output of to_tsvector is changed if default_text_search_config
>>> changes.
>>
>> It wuoldn't actually *corrupt* the index, right? You could end up with
>> wrong results, which might be regarded as corruption in one way, but as
>> long as you change the value back the index still works, no?
>
> Right, it would _temporarily_ corrupt it.  ;-)
>
>>> We have a few possible options:
>>>
>>> 	1) Document the problem and do nothing else.
>>> 	2) Make default_text_search_config a postgresql.conf-only
>>> 	   setting, thereby making it impossible to change by non-super
>>> 	   users, or make it a super-user-only setting.
>>> 	3) Remove default_text_search_config and require the
>>> 	   configuration to be specified in each function call.
>>>
>>> If we remove default_text_search_config, it would also make ::tsvector
>>> casting useless as well.
>>
>> I think 3 is a really bad solution.
>>
>> 2 is a half-bad solution. Do we have a way to say that it can be set at
>> database-level for example, but not at user session? Making it
>> superuser-only to change it but not postgresql.conf-only could accomplish
>> that, along with warnings in the docs for the super user about the effects
>> on current indexes by changing it.
>
> OK, here is what I am thinking.  If we make default_text_search_config
> super-user-only, then the user can't do SET (using "zero_damaged_pages"
> as a superuser-only example):
>
> 	test=> set zero_damaged_pages = on;
> 	ERROR:  permission denied to set parameter "zero_damaged_pages"
>
> 	test=> alter user guest set zero_damaged_pages = on;
> 	ERROR:  permission denied to set parameter "zero_damaged_pages"
>
> but the super-user can set it in postgresql.conf, or:
>
> 	test=# alter user guest set zero_damaged_pages = on;
> 	ALTER ROLE
>
> or
>
> 	test=# alter database vendor3 set zero_damaged_pages = on;
> 	ALTER ROLE
>
> meaning while it will be super-user-only, the administrator can set the
> default for specific databases and users.  Is that the best approach?
>
> A user can still over-ride the default by specifying the configuration
> in the function call.

This is ok, but it will not work in hosting environment and still 
doesn't prevent errors.

 	Regards,
 		Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83