How to diagnose and fix the 25003 inappropriate_access_mode_for_branch_transaction error code in Postgres.

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The 25003 error code inappropriate_access_mode_for_branch_transaction in PostgreSQL indicates that there is an attempt to prepare a transaction as a two-phase commit while the transaction is in an inappropriate access mode. This typically happens when you try to prepare a transaction for a two-phase commit inside a read-only transaction or when using a temporary table within the transaction.

To diagnose and fix this error, follow these steps:

  1. Check Transaction Access Mode: Ensure that the transaction is not read-only if you’re preparing it for a two-phase commit.
  2. Avoid Temporary Tables: Do not use temporary tables in transactions that you intend to prepare for a two-phase commit.

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

Example 1: Preparing a Transaction in Read-Only Mode

-- Setting the transaction to read-only mode
BEGIN TRANSACTION READ ONLY;

-- Some operation
SELECT * FROM my_table;

-- Attempting to prepare the transaction will cause the 25003 error
PREPARE TRANSACTION 'my_prep_transaction';

Fix: Do not set the transaction to read-only mode if you intend to prepare it for a two-phase commit.

-- Correct transaction access mode
BEGIN;

-- Some operation
SELECT * FROM my_table;

-- Preparing the transaction
PREPARE TRANSACTION 'my_prep_transaction';

Example 2: Using Temporary Tables in a Transaction to be Prepared

-- Starting a transaction
BEGIN;

-- Creating a temporary table
CREATE TEMP TABLE my_temp_table (id INT);

-- Attempting to prepare the transaction will cause the 25003 error
PREPARE TRANSACTION 'my_prep_transaction';

Fix: Avoid using temporary tables in transactions that will be prepared for a two-phase commit.

-- Starting a transaction
BEGIN;

-- Some operation that does not involve temporary tables
SELECT * FROM my_table;

-- Preparing the transaction
PREPARE TRANSACTION 'my_prep_transaction';

When you encounter the 25003 error, review your transaction to ensure that it is not read-only and does not include temporary tables before you attempt to prepare it for a two-phase commit. Adjust your transaction accordingly to comply with the requirements for a two-phase commit in PostgreSQL.

For more detailed information on transaction management and two-phase commits in PostgreSQL, you can refer to the PostgreSQL documentation on transaction control.

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