Re: Improvements in psql hooks for variables

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Daniel Verite" <daniel(at)manitou-mail(dot)org>
Cc: "Rahila Syed" <rahilasyed90(at)gmail(dot)com>, "Stephen Frost" <sfrost(at)snowman(dot)net>, "Ashutosh Bapat" <ashutosh(dot)bapat(at)enterprisedb(dot)com>, "pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>, "Andrew Dunstan" <andrew(at)dunslane(dot)net>
Subject: Re: Improvements in psql hooks for variables
Date: 2017-01-31 16:52:13
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"Daniel Verite" <daniel(at)manitou-mail(dot)org> writes:
> Tom Lane wrote:
>> One possible compromise that would address your concern about display
>> is to modify the hook API some more so that variable hooks could actually
>> substitute new values. Then for example the bool-variable hooks could
>> effectively replace "\set AUTOCOMMIT" by "\set AUTOCOMMIT on" and
>> "\unset AUTOCOMMIT" by "\set AUTOCOMMIT off", ensuring that interrogation
>> of their values always produces sane results.

> Agreed, that looks like a good compromise.

Attached is a draft patch for that. I chose to make a second hook rather
than complicate the assign hook API, mainly because it allows more code
sharing --- all the bool vars can share the same substitute hook, and
so can the three-way vars as long as "on" and "off" are the appropriate

I only touched the behavior for bool vars here, but if people like this
solution it could be fleshed out to apply to all the built-in variables.

Maybe we should merge SetVariableSubstituteHook and SetVariableAssignHook
into one function?

regards, tom lane

Attachment Content-Type Size
improve-psql-bool-var-behavior-1.patch text/x-diff 16.3 KB

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