From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgreSQL.org, Jan Wieck <jan@wi3ck.info>
Subject: Re: I propose killing PL/Tcl's "modules" infrastructure
Date: Sat, 25 Feb 2017 13:55:26 -0500
Message-ID: <33fe0208-74df-1a03-08af-9a4f0d1ed14d@2ndQuadrant.com> (raw)
In-Reply-To: <23184.1488048288@sss.pgh.pa.us>
References: <22067.1488046447@sss.pgh.pa.us>
<234c68e3-47ee-4db1-fe6d-6a5de56575b6@2ndQuadrant.com>
<23184.1488048288@sss.pgh.pa.us>
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On 02/25/2017 01:44 PM, Tom Lane wrote:
> Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:
>> On 02/25/2017 01:14 PM, Tom Lane wrote:
>>> Now, we could try to fix this bug, and add the regression test coverage
>>> that the code clearly lacks, and upgrade the documentation about it from
>>> its currently very sad state. But I think the right answer is just to
>>> remove the feature altogether. It's evidently not being used, and it's
>>> kind of insecure by design, and it would not be that hard for someone
>>> to provide equivalent functionality entirely in userland if they really
>>> wanted it.
>> In PLv8 we added a parameter plv8.start_proc that names a parameterless
>> function that's executed when plv8 is first called in each session. It
>> can be used quite easily to implement something like a modules
>> infrastructure - in fact I have used it to good effect for exactly that.
>> Maybe something similar for pltcl would be a good thing.
> Yeah, the only part that's even a bit hard to replicate in userland is
> initializing the autoloading mechanism in each session. It would be
> cleaner to provide a feature similar to what you describe that could
> be used for that purpose as well as others. However, where does the
> "parameterless function" come from? Is it a regular PLv8 (or for this
> purpose PL/Tcl) function expected to be present in pg_proc?
>
>
Yes, it's a regular PLv8 function.Here's an example. It presupposes that
there is a table called plv8_modules (modname text, code text,
load_on_start boolean).
CREATE OR REPLACE FUNCTION public.plv8_startup()
RETURNS void
LANGUAGE plv8
AS $function$
if (typeof plv8_loaded_modules == 'undefined')
plv8_loaded_modules = {};
load_module = function(modname)
{
if (plv8_loaded_modules[modname])
return;
var rows = plv8.execute("SELECT code from plv8_modules " +
" where modname = $1", [modname]);
for (var r = 0; r < rows.length; r++)
{
var code = rows[r].code;
eval("(function() { " + code + "})")();
// plv8.elog(NOTICE,"loaded module " + modname);
plv8_loaded_modules[modname] = 1;
}
};
reload_module = function(modname)
{
var rows = plv8.execute("SELECT code from plv8_modules " +
" where modname = $1", [modname]);
for (var r = 0; r < rows.length; r++)
{
var code = rows[r].code;
eval("(function() { " + code + "})")();
// plv8.elog(NOTICE,"loaded module " + modname);
plv8_loaded_modules[modname] = 1;
}
};
var rows = plv8.execute("SELECT modname, code from plv8_modules
where load_on_start");
for (var r = 0; r < rows.length; r++)
{
var modname = rows[r].modname;
if (plv8_loaded_modules[modname])
continue;
var code = rows[r].code;
eval("(function() { " + code + "})")();
plv8_loaded_modules[modname] = 1;
// plv8.elog(NOTICE,"loaded module " + modname);
};
$function$;
cheers
andrew
--
Andrew Dunstan https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: andrew.dunstan@2ndquadrant.com, tgl@sss.pgh.pa.us, jan@wi3ck.info
Subject: Re: I propose killing PL/Tcl's "modules" infrastructure
In-Reply-To: <33fe0208-74df-1a03-08af-9a4f0d1ed14d@2ndQuadrant.com>
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