Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Dmitry Dolgov <9erthalion6@gmail.com>, Michael Paquier <michael.paquier@gmail.com>, Arthur Zakirov <a.zakirov@postgrespro.ru>, Oleg Bartunov <obartunov@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, David Steele <david@pgmasters.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-01-11T19:20:52Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Jan 11, 2018 at 1:37 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Right, but in the case of stored arrays, we've decided that it *is*
>> our problem (as indeed it must be, because the user has no tools with
>> which they could fix a representation change for stored data).  The
>> question is to what extent that need would propagate to pseudo array
>> types.

> I think I view the rationale a bit differently.  Let's say that a user
> defines a composite type as (a int, b text) and uses that composite
> type as a column type.  Then, somebody tries to change column a to
> have type text, and suppose we don't throw an error but simply permit
> the operation.  If the user now tries to select from the offending
> column, the server will very likely crash.  In contrast, in the case
> where the user has defined an SQL function that selects $1.a and
> returns it as an int, they will get a runtime error when they try to
> use the function.  In my mind, that is the critical difference.

There are two critical differences --- that's one, and the other is
that there are SQL-level ways to fix the problem, ie change the function
text with CREATE OR REPLACE FUNCTION.  We don't have a SQL command that
says "now go update the representation of table T column C".

But I think we've probably beaten this topic to death ...

			regards, tom lane

Commits

  1. Throw error when assigning jsonb scalar instead of a composite object

  2. Filling array gaps during jsonb subscripting

  3. Implementation of subscripting for jsonb

  4. Allow ALTER TYPE to update an existing type's typsubscript value.

  5. Allow subscripting of hstore values.

  6. Support subscripting of arbitrary types, not only arrays.

  7. jit: Reference function pointer types via llvmjit_types.c.

  8. Teach contain_leaked_vars that assignment SubscriptingRefs are leaky.

  9. jit: Correct parameter type for generated expression evaluation functions.

  10. Renaming for new subscripting mechanism

  11. Fix assertion failure for SSL connections.

  12. Teach eval_const_expressions() to handle some more cases.