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base repository: postgresql-cfbot/postgresql
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  • 12 commits
  • 59 files changed
  • 2 contributors

Commits on Dec 18, 2025

  1. CREATE VARIABLE, DROP VARIABLE

    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  2. parsing session variable fences 

    The session variables can be used in query only inside the variable fence.
This is special syntax VARIABLE(varname), that eliminates a risk of
collision between variable and column identifier.

The session variables cannot be used as parameters of CALL or EXECUTE
commands. These commands evaluates arguments by direct call of expression
executor, and direct access to session variables from expression executor
will be implemented later (in next step)
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  3. collect session variables used in plan and assign paramid 

    In the plan stage we need to collect used session variables. On the
order of this list, the param nodes gets paramid (fix_param_node).
This number is used (later) as index to buffer of values of the
used session variables. The buffer is prepared and filled by executor.

Some unsupported optimizations are disabled:

* parallel execution
* simple expression execution in PL/pgSQL
* SQL functions inlining

Before execution of query with session variables we need to collect
used session variables. This list is used for loading variables to
executed query.

plan
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  4. fill an auxiliary buffer with values of session variables used in query 

    and locks variables used in query. Now we can read the content of any
session variable. Direct reading from expression executor is not allowed,
so we cannot to use session variables inside CALL or EXECUTE commands
(can be supported with direct access to session variables (from expression
executor) - postponed).

Using session variables blocks parallel query execution. It is not
technical problem (it just needs a serialization/deserialization of
es_session_varibles buffer), but it increases a size of patch (and then
it is postponed).
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  5. svariableReceiver 

    allows to store result of the query to session variable

Check correct format of result - one column, one row.
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  6. LET command - assign a result of expression to the session variable 

    The value is assigned to session variables usually by SET command. Unfortunately
there are two reasons why SET should not be used for this purpose in Postgres.

1. Using a_expr inside generic_set ram rule produces reduce conflicts, so it needs
   total reimplementation of related gram rules.

2. SET is no plan command - so it doesn't support usage of parameters.

3. Excepting implementation issues, there is fact, so if we use SET command
   for assigning values to session variables, then there can be collisions
   between session variables and GUC, and then we need some concepts, how
   these collisions should be solved, or how to protect self against these
   collisions. With the dedicated command, the collisions between GUC and session
   variables are not possible.

The command LET is executed as usual query execution. The result is stored
to the target session variable (resultVariable) by using VariableDestReceiver.

Implementations of EXPLAIN LET and PREPARE LET statements are not supported
now. Postponed to next step due reducing patch size.
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  7. DISCARD TEMP

    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  8. support CREATE IF NOT EXISTS and DROP IF EXISTS

    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  9. use names of currently used temp variables for tab complete of DROP V… 

    …ARIABLE, LET and VARIABLE()
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  10. transactional DDL - CREATE VARIABLE, DROP VARIABLE 

    Generally PostgreSQL DDL statements are transactional. We can implement transactional behave
for ( CREATE | DROP ) VARIABLE too. Implementation is almost simple. DROP just set dropped_lxid,
CREATE set created_lxid and moves previous entry of related sessionvars hashtab to stack. At the
end of transaction for commit we just clean this stack. For rollback we do copy the bootom value
from the stack and again clean stack.
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  11. subtransaction support for session variables DDL (CREATE, DROP) 

    If we support transactional DDL for CREATE, DROP session  variables, we should to
support subtransactions too. Implementation is simple. Any value has two new flags:
created_subid and dropped_subid. At the subtransaction end for rollback we
clean entries from the stack related to subtransactions. When commit we update
created_subid and dropped_subid for parent subtransaction.
    [email protected] authored and Commitfest Bot committed Dec 18, 2025
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  12. [CF 1608] v20251215 - 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/CAFj8pRBsbg7pEFN3GC8hj_Y3DK08QONseteeZZXyaXk_G8QnyA@mail.gmail.com
Author(s): Pavel Stehule
    Commitfest Bot committed Dec 18, 2025
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