How to diagnose and fix the 25006 read_only_sql_transaction error code in Postgres.

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The 25006 error code in PostgreSQL refers to a read_only_sql_transaction error, which occurs when you attempt to perform a write operation (such as INSERT, UPDATE, DELETE, or DDL commands) within a transaction that is set to read-only mode. In read-only mode, the transaction is not allowed to modify any data.

To diagnose and fix this error, follow these steps:

  1. Identify the Transaction Mode:
  • Check if the current transaction is set to read-only. This can usually be inferred from the error message itself or by checking the transaction settings in your session.
  1. Adjust Transaction Access Mode:
  • If you need to perform write operations, ensure that the transaction is not set to read-only. You can set the transaction to read-write mode before beginning your operations.
   -- Example: Starting a read-write transaction
   BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED READ WRITE;
   -- Perform your write operations here
   COMMIT;
  1. Review Application Logic:
  • If your application logic sets transactions to read-only, review the code to ensure that write operations are not mistakenly included within these transactions. Separate read-only and write operations into different transactions if necessary.
  1. Use Appropriate Transaction Blocks:
  • If certain operations should be read-only while others should allow writes, clearly separate these into different transaction blocks.
   -- Example: Separating read-only and read-write operations
   -- Read-only block
   BEGIN TRANSACTION READ ONLY;
   SELECT * FROM my_table;
   COMMIT;

   -- Read-write block
   BEGIN TRANSACTION READ WRITE;
   INSERT INTO my_table (column1) VALUES ('value1');
   COMMIT;
  1. Check for Implicit Transaction Settings:
  • Some database connection pools or ORMs may set transactions to read-only by default. Verify the configuration settings of your database connection to ensure it aligns with the intended behavior.
  1. Handle Read-Only Transactions in Replication or Standby Systems:
  • In replication or standby systems, the replica may be set to read-only. If you encounter this error in such a system, you may need to redirect write operations to the primary server or configure the replica to allow writes (if supported by your replication setup).

Here are some sample code snippets to illustrate how to handle this error:

-- Correct usage in a read-write transaction
BEGIN;
SET TRANSACTION READ WRITE;
UPDATE my_table SET column1 = 'new_value' WHERE id = 1;
COMMIT;

-- Incorrect usage in a read-only transaction
BEGIN;
SET TRANSACTION READ ONLY;
-- This next line will cause the 25006 error
UPDATE my_table SET column1 = 'new_value' WHERE id = 1;
-- To fix the error, either remove the write operation from the read-only transaction
-- or change the transaction to read-write mode.
COMMIT;

Remember to always commit or roll back your transactions to release any locks and resources held by the transaction. Proper transaction management will help prevent the 25006 error code from occurring.

For further guidance, refer to the official PostgreSQL documentation on transaction modes.

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