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Re: pl/{perl,pgsql} (was Re: AW: [HACKERS] triggers, views and rules (not instead))

From: jwieck(at)debis(dot)com (Jan Wieck)
To: brett(at)work(dot)chicken(dot)org (Brett McCormick)
Cc: vadim(at)sable(dot)krasnoyarsk(dot)su, root(at)bigfoot(dot)speakeasy(dot)org, root(at)eve(dot)speakeasy(dot)org, Andreas(dot)Zeugswetter(at)telecom(dot)at, jwieck(at)debis(dot)com, pgsql-hackers(at)hub(dot)org, mgittens(at)gits(dot)nl, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: pl/{perl,pgsql} (was Re: AW: [HACKERS] triggers, views and rules (not instead))
Date: 1998-02-23 09:41:12
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Lists: pgsql-hackers
Brett wrote:
> On Sun, 22 February 1998, at 18:26:45, Vadim B. Mikheev wrote:
> > ??? Old instance rules system was removed by Jolly & Andrew and so
> > it never supported SQL. I hope that Jan will give us PL/pgSQL soon
> > and it will be used for triggers, without changing current trigger
> > implementation...
> Is develemopment being done for PL/pgSQL?  What are peoples ideas for
> this?  I've never used a commercial db before, and the free ones don't
> usualle have a stored PL language.  What sort of things are you guys
> anticipating?  In the writing of PL/perl i've been tempted to give
> lots of access to the backend internals from perl (why not, it should
> have all the facilities C function programmers have!)  What do you think?

    No  actual  development  -  just have something in mind how I
    would implement it. I'll get into details after 6.3  release.
    PL/pgSQL will have at least the following capabilities:

        - local variable
        - local records
        - access to the database over SPI
        - control structures (if/else/while/loop)
        - elog messages
        - triggers can modify new tuple
        - triggers can skip operation

    Why  not handing many backend internals through a PL? Just to
    let  ordinary  users  use  the  language   without   breaking
    security.   The  implementation  of  PL/Tcl  uses  a safe Tcl
    interpreter for the evaluation of the Tcl  functions/trigger-
    procedures.  A  safe Tcl interpreter has very limited command
    set. No access to filesystem, no  access  to  networking,  no
    loading of other packages so nothing dangerous.

    If  perl doesn't have such a restricted interpreter facility,
    then perl might never become a  TRUSTED  procedural  language
    like  Tcl  is.  Remember, if the PL/perl implementation gives
    an ordinary user the right just to open a file for writing, a
    function  independent  who  created  it could damage database
    files directly. This MUST be  restricted  to  superusers  and
    this is the reason why the C language isn't TRUSTED.

> Also, as far as argument passing goes: strings & numbers get passed as
> perl scalars, and most other types get passed as a Posgres::Type
> object (with methods for conversion etc).  Right now I've got a switch
> block on the type oid and I have many case statements and a few bodies
> for these conversions.
> The conversions are hard-coded in the .c file (via the case
> statements).  The only reason any particular input type shows up in
> perl any particular way (as a scalar (string/int) or Postgres::Type)
> is because there's a hardcoded case statement for it.  Of course, the
> default is a Postgres::Type.  Which means new integer types show up as
> a Postgres::Type, which could be considered a bad thing.  Right now
> part of what i'm doing is checking the typbyval and then passing that
> type as an integer scalar (excluding selected types that don't make
> sense as ints)..  Maybe the default case should be the types ouptut
> function?

    Whatever  perl  scalars  are  - don't know. Tcl is happy with
    string representation of anything on the evaluation level and
    Tcl_Eval()  leaves  a  string in the interpreter result. So I
    used  the  registered  input/output  functions   to   convert
    anything   from/into   strings   to   communicate   with  the

    Whatever is given to or  returned  from  a  Tcl  function  in
    PL/Tcl  will  be in the external representation. This is what
    the user sees if he selects from a table in psql and what has
    to  be  given  on  insert/update.  So  on  the  PL/Tcl level,
    anything is the external representation  as  defined  by  the
    types  registered  input/output functions. This is the values
    format humans deal with best.

    I know that the way I choose isn't the performance  optimized
    one.   But  blowing  up the functions code by handling binary
    data wouldn't be either.

    When implementing perl or Tcl as a  procedural  language,  we
    must   satisfy   the  need  of  perl/Tcl  programmers.  These
    programmers must not have any C skill,  but  they  sure  will
    know   how   to   read/create   a   string  in  the  external
    representation. For some types (especially for  user  created
    types)  it  might  be hard to figure out what each bit in the
    binary Datum is for if you aren't familiar with C.



# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#======================================== jwieck(at)debis(dot)com (Jan Wieck) #

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