Message-ID: <52369651.7000208@uptime.jp>
Date: Mon, 16 Sep 2013 14:25:37 +0900
From: Satoshi Nagayasu <snaga@uptime.jp>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Andres Freund <andres@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>,
 Fujii Masao <masao.fujii@gmail.com>,
 Michael Paquier <michael.paquier@gmail.com>,
 Jim Nasby <jim@nasby.net>, Greg Stark <stark@mit.edu>,
 Hannu Krosing <hannu@2ndquadrant.com>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: pg_system_identifier()
References: <20130822162019.GC10710@eldon.alvh.no-ip.org>
 <20130822163059.GI17006@awork2.anarazel.de> <15653.1377189456@sss.pgh.pa.us>
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 <521A8985.2040509@nasby.net>
 <CAB7nPqSx+GEROLiCMOYBCDimARQauEe=2TDSZmFEjZYnV6yBKw@mail.gmail.com>
 <CAHGQGwH5K9Dm+td00AE9Gwby92fzOJC4mXcjgerYtq+GqxUZhw@mail.gmail.com>
 <WM!4a186afed707ebaddcd3a5f21382e12ef6a9d1c73e47f0b5fcf94a69469174a622e24aa2d786ae1c7e4e1f07993de908!@asav-1.01.com>
 <521B8C1E.9000808@agliodbs.com> <20130826184546.GB5464@awork2.anarazel.de>
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Hi,

I'm catching up with the discussion as a reviewer...

(2013/08/27 5:35), Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
>> On 2013-08-26 10:10:54 -0700, Josh Berkus wrote:
>>> I'm going to reverse my vote, and vote against this patch.  The reason
>>> why is that I think we should instead have a function:
>>>
>>> pg_controldata(parameter text)
>>>
>>> ... which would report *all* strings in pg_controldata.  Hence, you'd do
>>> instead:
>>>
>>> pg_controldata('system identifier')
>>>
>>> This will hopefully spare us from 15 patches incrementally adding all of
>>> the individual items in controldata.
> 
>> If anything but the proposed feature, it should be an SRF - passing in
>> text parameters isn't very discoverable.
> 
> I'm not pleased with the idea that we'd have to dumb all the relevant
> datatypes down to text so that we could push them through this single
> function.
> 
> Also, what about i18n?  pg_controldata localizes all the strings it
> prints, but I doubt that's a great idea for either the input or the
> output of this proposed function.

How about adding new system view with new function which returns
a single pg_controldata value in text type, and using a cast for
each column in the view definition?

CREATE VIEW pg_catalog.pg_controldata AS
  SELECT pg_controldata('control_version')::integer AS control_version,
         pg_controldata('catalog_version')::integer AS catalog_version,
         pg_controldata('system_identifier')::bigint AS system_identifier,
         ...
         pg_controldata('next_xlog_file')::char(25) AS next_xlog_file,
         ...
         pg_controldata('encoding')::text AS encoding;

Given that the view can work like a SRF, and it allows us to retrieve
all the values of pg_controldata with appropriate types in single
record from the view:

  select * from pg_catalog.pg_controldata;

To get the system identifier value:

  select system_identifier from pg_catalog.pg_controldata;

Regards,
-- 
Satoshi Nagayasu <snaga@uptime.jp>
Uptime Technologies, LLC. http://www.uptime.jp


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