Re: pg_sequence catalog

From: Andreas Karlsson <andreas(at)proxel(dot)se>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Craig Ringer <craig(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_sequence catalog
Date: 2016-11-08 23:43:03
Message-ID: 9f4b68f1-d424-f166-08ef-3bcaf9be8dcc@proxel.se
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Review of the pg_sequences view.

This seems like a useful addition to me, making life easier for
administrators and monitoring tools. While there is already a view in
information_schema it is missing cache_size and last_value.

= Functional review

- The patch applies and passes the test suite without any issue.

- A worry is that it might get a bit confusing to have both the future
catalog pg_sequence and the view pg_sequences.

- I think it would be useful to include is_cycled in the view.

- When creating a temporary sequences and then running "SELECT * FROM
pg_sequences" in another session I get the following error.

ERROR: cannot access temporary tables of other sessions

- Shouldn't last_value be NULL directly after we have created the
sequence but nobody has called nextval() yet?

- I noticed that last_value includes the cached values, but that also
seems to me like the correct thing to do.

- I do not like the name of the new function, lastval(regclass). I think
like you suggested it would be better with something more verbose.
sequence_lastval()? sequence_last_value()?

= Code

- There is an XXX comment still in the code. It is about the name of the
lastval1() function.

= Documentation

- The documentation does not mention the last_value column.

- The extra empty line after "</table>" does not fit with the formatting
of the rest of the SGML file.

Andreas

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