How to diagnose and fix the 25000 invalid_transaction_state error code in Postgres.

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The 25000 error code in PostgreSQL indicates an invalid_transaction_state. This error suggests that there is an issue with the current state of the transaction, such as attempting an operation that isn’t allowed within the current transaction block, or there are issues with transaction boundaries.

Here are some examples and sample code to explain and cover the possibilities:

Example 1: Issuing Transaction Control Commands in the Wrong Context

If you issue a transaction control command like COMMIT or ROLLBACK when there is no transaction block, you’ll encounter the 25000 error.

-- This will raise an error if not executed inside a transaction block
COMMIT;

Fix:

Ensure that you only issue COMMIT or ROLLBACK within a valid transaction block.

-- Start a transaction block before issuing transaction control commands
BEGIN;
-- Your transactional operations here
COMMIT;

Example 2: Nested Transactions Not Handled Properly

PostgreSQL does not support real nested transactions. Attempting to start a new transaction with BEGIN inside an existing transaction block without using savepoints can lead to the 25000 error.

-- Start of the first transaction block
BEGIN;

-- Attempt to start a nested transaction
BEGIN; -- This will raise an error

Fix:

Use savepoints for handling nested transactions.

-- Start of the first transaction block
BEGIN;

-- Create a savepoint instead of starting a new transaction
SAVEPOINT my_savepoint;

-- Operations that you want to be able to roll back to the savepoint

-- If needed, you can roll back to the savepoint
ROLLBACK TO SAVEPOINT my_savepoint;

-- Commit the transaction
COMMIT;

Example 3: Preparing a Transaction in a Prohibited Context

Trying to prepare a transaction for two-phase commit when there are active subtransactions or when you’re not in a transaction block can result in the 25000 error.

-- Trying to prepare a transaction without a proper transaction block
PREPARE TRANSACTION 'my_transaction';

Fix:

Ensure that you’re in a proper transaction block and that all subtransactions have been completed.

-- Start a transaction block
BEGIN;

-- Perform your transactional operations here

-- Prepare the transaction for a two-phase commit
PREPARE TRANSACTION 'my_transaction';

Example 4: Accessing Data After PREPARE TRANSACTION

After a transaction is prepared with PREPARE TRANSACTION, trying to execute further commands before completing the two-phase commit can lead to the 25000 error.

-- Start a transaction block
BEGIN;

-- Perform some operations

-- Prepare the transaction
PREPARE TRANSACTION 'my_transaction';

-- Trying to execute further commands will raise an error
INSERT INTO my_table VALUES ('some_data');

Fix:

Complete the two-phase commit process before executing further commands.

-- Start a transaction block
BEGIN;

-- Perform some operations

-- Prepare the transaction
PREPARE TRANSACTION 'my_transaction';

-- Commit or Rollback the prepared transaction
COMMIT PREPARED 'my_transaction';
-- or
ROLLBACK PREPARED 'my_transaction';

-- Now you can continue with other operations
INSERT INTO my_table VALUES ('some_data');

To diagnose 25000 errors, you should check the transaction control logic in your SQL scripts or application code, ensuring that transaction blocks are properly initiated and terminated, and that commands are issued in a context that is consistent with the current transaction state.

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