Re: Is the subtype_diff function in CREATE TYPE only can be C function?

[ddme]

> 2024年1月10日 18:04，Ashutosh Bapat  写道：
> 
> On Wed, Jan 10, 2024 at 1:49 PM ddme  <mailto:ret2d...@qq.com>> wrote:
>> 
>> Hi all,
>> 
>> I notice that the CREATE TYPE syntax can specify subtype_diff function
>> 
>> CREATE TYPE name AS RANGE (
>>SUBTYPE = subtype
>>[ , SUBTYPE_OPCLASS = subtype_operator_class ]
>>[ , COLLATION = collation ]
>>[ , CANONICAL = canonical_function ]
>>[ , SUBTYPE_DIFF = subtype_diff_function ] <— here
>>[ , MULTIRANGE_TYPE_NAME = multirange_type_name ]
>> )
>> 
>> And a example is
>> ```sql
>> 
>> CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = 
>> float8mi);
>> 
>> ```
>> 
>> I notice that float8mi is a C function, and I find the call_subtype_diff() 
>> in source code that it seems only can call C function.
> 
> call_subtype_diff() invokes FunctionCall2Coll() which in turn invokes
> the function handler for non-C functions. See
> fmgr_info_cxt_security() for example. So subtype_diff can be a SQL
> callable function written in any supported language.
> 
>> 
>> I want to know
>> 
>> 1. Can the subtype_diff function in CREATE TYPE be sql or plpgsql function?
> 
> I think so.
> 
>> 2. How to call subtype_diff function? I know it related with GiST index, I 
>> need a example on how to trigger subtype_diff function.
> 
> I am not familiar with GiST code enough to answer that question. But
> looking at the places where call_subtype_diff() is called, esp. the
> comments there might give you hints.
> OR somebody more familiar with GiST code will give you a direct answer.
> 
> -- 
> Best Wishes,
> Ashutosh Bapat

Thank you!


I know that range_gist_picksplit call call_subtype_diff() but I find not call 
path for range_gist_picksplit.
I have try to trigger  GiST index like `CREATE INDEX … USING GIST` and using 
select with filter to trigger index. With the help of EXPLAIN, I get that the 
gist index have been triggered but subtype_diff function have not


```sql
create function float4mi(a float8, b float8) RETURNS float8 LANGUAGE SQL … …

create type float8range as range (subtype=float8, subtype_diff=float4mi);
create table float8range_test(f8r float8range);
insert into float8range_test values('[1.111,2.344]'::float8range), ('[1.111, 
4.567]'::float8range);
create index my_index on float8range_test using gist(f8r);
SET enable_seqscan = off;
select * from float8range_test ORDER BY f8r;
```

Is there need more setup SQL like `CREATE OPERATOR CLASS … USING gist` to 
trigger?

Is the subtype_diff function in CREATE TYPE only can be C function?

[ddme]

Hi all,

I notice that the CREATE TYPE syntax can specify subtype_diff function
CREATE TYPE name AS RANGE (
SUBTYPE = subtype
[ , SUBTYPE_OPCLASS = subtype_operator_class ]
[ , COLLATION = collation ]
[ , CANONICAL = canonical_function ]
[ , SUBTYPE_DIFF = subtype_diff_function ] <— here
[ , MULTIRANGE_TYPE_NAME = multirange_type_name ]
)
And a example is
```sql
CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi);
```

I notice that float8mi is a C function, and I find the call_subtype_diff() in 
source code that it seems only can call C function.

I want to know

1. Can the subtype_diff function in CREATE TYPE be sql or plpgsql function?
2. How to call subtype_diff function? I know it related with GiST index, I need 
a example on how to trigger subtype_diff function.

What’s more,  I want to learn how Postgres kernel call subtype_diff function 
(in which source file or function), that will help me a lot.
 

Thank you all!