Re: proposal: schema variables - Mailing list pgsql-hackers
| From | Asif Rehman |
|---|---|
| Subject | Re: proposal: schema variables |
| Date | |
| Msg-id | CADM=Jej3onf9VK_3BfsuCpRLnXrYKp+cCY2PtahpCXRY4jG1iw@mail.gmail.com Whole thread Raw |
| In response to | Re: proposal: schema variables (Pavel Stehule <pavel.stehule@gmail.com>) |
| Responses |
Re: proposal: schema variables
|
| 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 WITHSo the syntax can looks likeCREATE [ 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 forsyntax CREATE IMMUTABLE VARIABLE for define constants.second try to fix pg_dumpRegardsPavelSee attached patchRegardsPavel?RegardsPavel
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 inmake[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 FUNCTIONpostgres=# create schema test;CREATE SCHEMApostgres=# create variable test.v1 as timestamp default foofunc();CREATE VARIABLEpostgres=# drop function foofunc();DROP FUNCTIONpostgres=# 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 VARIABLEpostgres=# 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;LETpostgres=# 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
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