Re: proposal: schema variables - Mailing list pgsql-hackers

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

pá 28. 2. 2020 v 16:30 odesílatel Pavel Stehule <pavel.stehule@gmail.com> napsal:

čt 27. 2. 2020 v 15:37 odesílatel Pavel Stehule <pavel.stehule@gmail.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