Re: [HACKERS] proposal: schema variables

Hi,

I plan to make usability and feature test review in several days.

Is there any chances that it will work on replicas?
Such possibility is very helpful in generating reports.
Now, LET command produces an error:

ERROR:  cannot execute LET in a read-only transaction

But if we say that variables are non-transactional ?

-----
Pavel Luzanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Hi

2018-02-07 7:34 GMT+01:00 Pavel Stehule <pavel.stehule@gmail.com>:

Hi

updated patch with your changes in documentation and pg_dump (initial) support

Main issue of this patch is storage. We can reuse local buffers used for temp tables. But it does allocation by 8KB and it creates temp files for every object. That is too big overhead. Storing just in session memory is too simple - then there should be lot of new code used, when variable will be dropped.

I have ideas how to allow work with mix of scalar and composite types - so it will be next step of this prototype.

Regards

Pavel

new update - rebased, + some initial support for composite values on right side and custom types, arrays are supported too.

omega=# CREATE VARIABLE xx AS (a int, b numeric);
CREATE VARIABLE
omega=# LET xx = (10, 20)::xx;
LET
omega=# SELECT xx;
+---------+
|   xx    |
+---------+
| (10,20) |
+---------+
(1 row)

omega=# SELECT xx.a + xx.b;
+----------+
| ?column? |
+----------+
|       30 |
+----------+
(1 row)

omega=# \d xx
schema variable "public.xx"
+--------+---------+
| Column |  Type   |
+--------+---------+
| a      | integer |
| b      | numeric |
+--------+---------+

Regards

Pavel