Re: proposal: schema variables

On Sat, Feb 29, 2020 at 2:10 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

>
>
> pá 28. 2. 2020 v 16:30 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> napsal:
>
>>
>>
>> čt 27. 2. 2020 v 15:37 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
>> napsal:
>>
>>>
>>> Hi
>>>
>>>
>>>> 3) Any way to define CONSTANTs ?
>>>> We already talked a bit about this subject and also Gilles Darold
>>>> introduces it in this mailing-list topic but I'd like to insist on it.
>>>> I think it would be nice to have a way to say that a variable should
>>>> not be changed once defined.
>>>> Maybe it's hard to implement and can be implemented later, but I just
>>>> want to know if this concern is open.
>>>>
>>>
>>> I played little bit with it and I didn't find any nice solution, but
>>> maybe I found the solution. I had ideas about some variants, but almost all
>>> time I had a problem with parser's shifts because all potential keywords
>>> are not reserved.
>>>
>>> last variant, but maybe best is using keyword WITH
>>>
>>> So the syntax can looks like
>>>
>>> CREATE [ TEMP ] VARIABLE varname [ AS ] type [ NOT NULL ] [ DEFAULT
>>> expression ] [ WITH [ OPTIONS ] '(' ... ')' ] ]
>>>
>>> What do you think about this syntax? It doesn't need any new keyword,
>>> and it easy to enhance it.
>>>
>>> CREATE VARIABLE foo AS int DEFAULT 10 WITH OPTIONS ( CONSTANT);
>>>
>>
>> After some more thinking and because in other patch I support syntax
>> CREATE TRANSACTION VARIABLE ... I change my opinion and implemented support
>> for
>> syntax CREATE IMMUTABLE VARIABLE for define constants.
>>
>
> second try to fix pg_dump
>
> Regards
>
> Pavel
>
>
>>
>> See attached patch
>>
>> Regards
>>
>> Pavel
>>
>>
>>>
>>> ?
>>>
>>> Regards
>>>
>>> Pavel
>>>
>>>
>>>
Hi Pavel,

I have been reviewing the latest patch (schema-variables-20200229.patch.gz)
and here are few comments:

1- There is a compilation error, when compiled with --with-llvm enabled on
CentOS 7.

llvmjit_expr.c: In function ‘llvm_compile_expr’:
llvmjit_expr.c:1090:5: warning: initialization from incompatible pointer
type [enabled by default]
build_EvalXFunc(b, mod, "ExecEvalParamVariable",
^
llvmjit_expr.c:1090:5: warning: (near initialization for ‘(anonymous)[0]’)
[enabled by default]
llvmjit_expr.c:1090:5: warning: initialization from incompatible pointer
type [enabled by default]
llvmjit_expr.c:1090:5: warning: (near initialization for ‘(anonymous)[0]’)
[enabled by default]
llvmjit_expr.c:1090:5: warning: initialization from incompatible pointer
type [enabled by default]
llvmjit_expr.c:1090:5: warning: (near initialization for ‘(anonymous)[0]’)
[enabled by default]
llvmjit_expr.c:1090:5: warning: passing argument 5 of ‘build_EvalXFuncInt’
from incompatible pointer type [enabled by default]
llvmjit_expr.c:60:21: note: expected ‘struct ExprEvalStep *’ but argument
is of type ‘LLVMValueRef’
static LLVMValueRef build_EvalXFuncInt(LLVMBuilderRef b, LLVMModuleRef mod,
^
llvmjit_expr.c:1092:29: error: ‘i’ undeclared (first use in this function)
LLVMBuildBr(b, opblocks[i + 1]);
^
llvmjit_expr.c:1092:29: note: each undeclared identifier is reported only
once for each function it appears in
make[2]: *** [llvmjit_expr.o] Error 1

After looking into it, it turns out that:
- parameter order was incorrect in build_EvalXFunc()
- LLVMBuildBr() is using the undeclared variable 'i' whereas it should be
using 'opno'.

2- Similarly, If the default expression is referencing a function or object,
dependency should be marked, so if the function is not dropped silently.
otherwise, a cache lookup error will come.

postgres=# create or replace function foofunc() returns timestamp as $$
begin return now(); end; $$ language plpgsql;
CREATE FUNCTION
postgres=# create schema test;
CREATE SCHEMA
postgres=# create variable test.v1 as timestamp default foofunc();
CREATE VARIABLE
postgres=# drop function foofunc();
DROP FUNCTION
postgres=# select test.v1;
ERROR: cache lookup failed for function 16437

3- Variable DEFAULT expression is apparently being evaluated at the time of
first access. whereas I think that It should be at the time of variable
creation. consider the following example:

postgres=# create variable test.v2 as timestamp default now();
CREATE VARIABLE
postgres=# select now();
now
-------------------------------
2020-03-05 12:13:29.775373+00
(1 row)
postgres=# select test.v2;
v2
----------------------------
2020-03-05 12:13:37.192317 -- I was expecting this to be earlier than the
above timestamp.
(1 row)

postgres=# select test.v2;
v2
----------------------------
2020-03-05 12:13:37.192317
(1 row)
postgres=# let test.v2 = default;
LET
postgres=# select test.v2;
v2
----------------------------
2020-03-05 12:14:07.538615
(1 row)

To continue my testing of the patch I made few fixes for the above-mentioned
comments. The patch for those changes is attached if it could be of any use.

--
Asif Rehman
Highgo Software (Canada/China/Pakistan)
URL : www.highgo.ca