Re: proposal: schema PL session variables - Mailing list pgsql-hackers
| From | Pavel Stehule |
|---|---|
| Subject | Re: proposal: schema PL session variables |
| Date | |
| Msg-id | CAFj8pRB51pQvSr4uYmXu6efNQEvaVbvz28XnjHw13x9u0f53eQ@mail.gmail.com Whole thread Raw |
| In response to | Re: proposal: schema PL session variables (Pavel Stehule <pavel.stehule@gmail.com>) |
| List | pgsql-hackers |
Hi
2016-02-23 20:52 GMT+01:00 Pavel Stehule <pavel.stehule@gmail.com>:
2016-02-12 22:41 GMT+01:00 Jim Nasby <Jim.Nasby@bluetreble.com>:On 2/12/16 2:58 PM, Pavel Stehule wrote:
So I think adding something like this needs to at least address
*how* SQL level access would work, *when* it's eventually implemented.
I understand - and I agree.
small note: Private variables should not be executed from any SQL,
because SQL has not directly related schema. It can be executed only
from SQL embedded in some object with attached schema - PL functions,
views, constraints, .. So for this use case, the important information
is info about a container. We have to hold info about related schema in
planner/executor context.
I think that's probably true, but this also shows why we need to consider different PLs too. As it stands right now, the only way to access a variable outside of plpgsql would be to call a plpgsql function, and currently there's no way to make a plpgsql function private. So for this to work, private variables probably need to be exposed directly through the pl handler.
Again, I'm not saying this all has to be implemented up front, but there needs to be a plan for how it would work.
I think it would be a good idea to start a wiki page on this topic to start collecting stuff together.I wrote some basic info - https://wiki.postgresql.org/wiki/CREATE_PRIVATE_VARIABLE
I though about this feature and now I am thinking so it is really similar to sequences. Sure there are differences - but a workflow is pretty similar. Created, dropped by CREATE, DROP statements, accessed with functions everywhere (and in some iteration directly in PLpgSQL). The content can be of any type stored in memory - session or transaction closed. In first iteration initialized on default value when it is first accessed in scope. Accessibility can be controlled by rights to schema.
syntax:
CREATE (SESSION|TRANSACTION) VARIABLE schema.xx datatype DEFAULT ...;
DROP VARIABLE schema.xx;
Access:
SELECT setvar(regclass, "any"); -- supported by Parser - enforcing "any" to datatype
SELECT getvar(regclass) -- returns "any" -- supported by Parser -- enforcing "any" to datatype
The access rights on variables can be exactly same like rights on sequences.
Regards
Pavel
I changed my opinion on initialization part. The private variables with non null default should be initialized in session start. It is much more practical and it can be used for triggering some ON CONNECT custom routines.RegardsPavel
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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