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  • 9 commits
  • 117 files changed
  • 3 contributors

Commits on May 20, 2025

  1. Enhancing catalog for support session variables and related support 

    This patch introduces new system catalog table pg_variable. This table holds metadata about
session variables created by command CREATE VARIABLE, and dropped by command DROP VARIABLE.
Both commands are implemented by this patch. Possibility to change owner, schema or rename.

Access to session variables can be controlled by SELECT or UPDATE rights. Both rights are
introduced by this patch too.

This patch enhancing pg_dump and psql to support session variables. The changes are related
to system catalog.

This patch is not short, but the code is simple.
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  2. Storage for session variables and SQL interface 

    Session variables are stored in session memory in a dedicated hash table.
They are set by the LET command and read by the SELECT command.
The access rights should be checked.

The identifiers of session variables should always be shadowed by possible
column identifiers: we don't want to break an application by creating some
badly named session variable.

The limits of this patch (solved by other patches):

- session variables block parallel execution
- session variables blocks simple expression evaluation (in plpgsql)
- SQL functions with session variables are not inlined
- CALL statement is not supported (usage of direct access to express executor)
- EXECUTE statement is not supported (usage of direct access to express executor)
- memory used by dropped session variables is not released

Implementations of EXPLAIN LET and PREPARE LET statements
are in separate patches (for better readability)
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  3. function pg_session_variables for cleaning tests 

    This is a function designed for testing and debugging.  It returns the
content of sessionvars as-is, and can therefore display entries about
session variables that were dropped but for which this backend didn't
process the shared invalidations yet.
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  4. DISCARD VARIABLES 

    Implementation of DISCARD VARIABLES commands by removing hash table with session variables
and resetting related memory context.
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  5. memory cleaning after DROP VARIABLE 

    Accepting a sinval message invalidates entries in the "sessionvars" hash table.
These entries are validated before any read or write operations on session variables.
When the entry cannot be validated, it is removed.  Removal will be delayed when
the variable was dropped by the current transaction, which could still be rolled back.
    @laurenz
    laurenz authored and Commitfest Bot committed May 20, 2025
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  6. plpgsql tests

    @laurenz
    laurenz authored and Commitfest Bot committed May 20, 2025
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  7. GUC session_variables_ambiguity_warning 

    Inside an query the session variables can be shadowed. This behaviour is by design,
because this ensuring so new variables doesn't break existing queries. But this
behaviour can be confusing, because shadowing is quiet.

When new GUC session_variables_ambiguity_warning is on, then the warning
is displayed, when some session variable can be used, but it is not used
due shadowing. This feature should to help with investigation of unexpected
behaviour.

Note: PLpgSQL has an option that controls priority of identifier's spaces
(SQL or PLpgSQL). Default behaviour doesn't allows collisions. I believe
this default is the best. I cannot to implement similar very strict
behaviour to session variables, because one unhappy named session variable
can breaks an applications. The problems related to badly named PLpgSQL's
varible is limitted just to only one routine.
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  8. variable fence syntax support and variable fence usage guard support 

    this patch introduces a concept of variable fence - syntax for variable
reference `VARIABLE(varname)` that is not in collision with column reference.
When variable fence usage guard warning is active, then usage variable
without variable fence in the case, where there can be column references,
the the warning is raised.

initial implementation of variable fence
    okbob@github.com authored and Commitfest Bot committed May 20, 2025
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  9. [CF 1608] v20250515 - declarative session variables, LET command 

    This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/1608

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CAFj8pRCEjG005L=1vGbir-odYdcYxByOAeFVJ_K9eRcRF=MbNQ@mail.gmail.com
Author(s): Pavel Stehule
    Commitfest Bot committed May 20, 2025
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