Re: ALTER SYSTEM SET command to change postgresql.conf parameters (RE: Proposal for Allow postgresql.conf values to be changed via SQL [review])

On Thu, Aug 22, 2013 at 6:06 PM, Stephen Frost <sfrost@snowman.net> wrote:
> * Amit Kapila (amit.kapila16@gmail.com) wrote:
>>    This can resolve the problem of whether to read auto file rather
>> cleanly, so the idea is:
>>
>> Enable/Disable reading of auto file
>> -----------------------------------------------------
>> a. Have a new include in postresql.conf
>>     #include_auto_conf_file    postgresql.auto.conf
>>     as it is a special include, we can read this file relative to data
>> directory.
>>
>> Enable/Disable Alter System command
>> -----------------------------------------------------------
>> This can be achieved in 3 ways:
>> a. Check before executing Alter System if include directive is
>> disabled, then just issue a warning to user and proceed with command.
>> b. Check before executing Alter System if include directive is
>> disabled, then just issue an error and stop.
>
> It doesn't make sense for it to be a 'warning' with this- the
> parameter specifies the file to use.  If you don't know what file to
> use, how you can possibly do anything but return an error?
  As the file and location are fixed, we can go-ahead and write to
it, but I think now we are deciding  if someone disables include dir, then we can just disable Alter
System, so it is better to return error in such  situation.

> Note that I *like* that about this approach.
>
> There are a few other considerations with this-
>
> - What should the default be?  (Still thinking 'off' myself)    default 'off' is a safe option, as it won't allow
usersto make
 
any change to parameter values until/unless they    read from manual, how to use it and what can go wrong, on the
other side it will be bit hassle for user to use this    command. I think 'on' would be better.
> - What happens if the user specifies 'postgresql.conf'?  I'm thinking we
>   would disallow such insanity (as that's what it is, imv..) by having
>   an identifier in the file that this is the PG "auto conf" file.         I think we can detect by name and give
error.
> - Should we have such an identifier in auto.conf to indicate that we
>   created it, to prevent the user from setting it to something they
>   shouldn't?    I think if user plays with this file manually, it can lead to
problems, that's why earlier we have    decided to keep a note on top of file which will indicate, do not
edit this file manually.    I believe that should be sufficient.

> - What's the "bootstrap" mode; iow, if a user enables the option but the
>   file doesn't exist, what do we do?  With this approach, I'd be
>   inclined to say we simply create it and put the marker to indicate
>   it's "our" file.
    Alter System will create the file if doesn't exist.

> - Should we allow it to be outside of the data dir?  We could simply log
>   an error and ignore the parameter if it's more than a simple filename.
    This should be an error, the file location and name will be fixed.


With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com