How to diagnose and fix the 25001 active_sql_transaction error code in Postgres.

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The 25001 error code in PostgreSQL, active_sql_transaction, occurs when you attempt to execute a command that cannot be run inside a transaction block. Certain commands, like CREATE DATABASE, DROP DATABASE, and VACUUM (with certain options), must be run outside of any transaction.

Here are several examples and solutions for fixing this error:

Example 1: Creating a Database Inside a Transaction Block

Attempting to create a database within a transaction block will trigger the 25001 error.

-- Incorrect way that causes error 25001
BEGIN;
CREATE DATABASE new_database;
COMMIT;

-- Correct way
-- Run the command outside of a transaction block
CREATE DATABASE new_database;

Example 2: Dropping a Database Inside a Transaction Block

Similar to creating a database, dropping a database within a transaction block is not allowed.

-- Incorrect way that causes error 25001
BEGIN;
DROP DATABASE old_database;
COMMIT;

-- Correct way
-- Run the command outside of a transaction block
DROP DATABASE old_database;

Example 3: Running VACUUM FULL Inside a Transaction Block

VACUUM FULL cannot be executed inside a transaction block.

-- Incorrect way that causes error 25001
BEGIN;
VACUUM FULL my_table;
COMMIT;

-- Correct way
-- Run the command outside of a transaction block
VACUUM FULL my_table;

Example 4: Using Certain Commands in PL/pgSQL Functions

PL/pgSQL functions are executed within a transaction block by default. If you try to include commands that cannot run inside a transaction block, you will get the 25001 error.

-- Incorrect function that will cause error 25001 when called
CREATE OR REPLACE FUNCTION create_new_database() RETURNS void AS $$
BEGIN
    CREATE DATABASE new_database;
END;
$$ LANGUAGE plpgsql;

-- Correct approach
-- Avoid including such commands in functions
-- Instead, run them as standalone commands
CREATE DATABASE new_database;

Example 5: Using Database Migration Tools

When using database migration tools, ensure that commands that cannot run inside a transaction are executed in their own separate migration files without transaction wrapping.

-- Incorrect migration file that causes error 25001
BEGIN;
CREATE DATABASE new_database;
COMMIT;

-- Correct migration file
-- Do not include BEGIN/COMMIT to ensure it runs outside a transaction
CREATE DATABASE new_database;

To avoid the 25001 error, always check the PostgreSQL documentation to see if the command you are executing is allowed within a transaction block. If you encounter this error, the solution is typically to remove the command from the transaction block or to execute it in a separate session where no transaction has been initiated.

For more information on transaction blocks and commands that cannot be run inside them, you can refer to the official PostgreSQL documentation which provides guidelines on the usage of transaction-sensitive commands.

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