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 ?
sure, it should to work. Now, I am try to solve a issues on concept level - the LET code is based on DML code base, so probably there is check for rw transactions. But it is useless for LET command.
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)