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RDS for PostgreSQL

Managing connection endpoints

Read/Write separation strategy

Once read/write separation is enabled, users' queries will be sent to the primary node or its read-only nodes. If you do not want an SQL query that meets the load balancing conditions to be sent to the primary node rather than through load balancing after read/write separation is enabled, you can add a hint before the SQL query. /*NO LOAD BALANCE*/ is usually used as the hint.

Queries sent to the primary node

Standard SQL queries

INSERT，UPDATE，DELETE，COPY FROM，TRUNCATE，CREATE，DROP，ALTER，COMMENT

SELECT ... FOR SHARE | UPDATE

DECLARE，FETCH，CLOSE

SHOW

Lock commands stricter than ROW EXCLUSIVE MODE

SELECT under transaction isolation SERIALIZABLE level

Part of the transactional commands:

BEGIN READ WRITE，START TRANSACTION READ WRITE

SET TRANSACTION READ WRITE，SET SESSION CHARACTERISTICS AS TRANSACTION READ WRITE

SET transaction_read_only = off

Two-phase commit commands: PREPARE TRANSACTION, COMMIT PREPARED, ROLLBACK PREPARED

LISTEN，UNLISTEN，NOTIFY

VACUUM

Commands for creating large objects

Multiple SQL commands on a single line

Some sequence manipulation functions (nextval and setval)

Custom SQL queries

The current RDS for PostgreSQL version defines some functions and SQL templates. Queries containing these functions or matching an SQL template will be forwarded to the primary node.

Queries containing the functions nextval, setval, lastval, currval, txid_current, gin_clean_pending_list

Queries containing functions prefixed with pg_catalog, pg_, current_, cursor_

Queries matching the template .*for update.*

Queries sent to read-only nodes

SELECT queries not included in the above

COPY TO STDOUT

EXPLAIN

EXPLAIN ANALYZE and the query is SELECT not including writing functions

Sent to the primary node and read-only node

DISCARD

DEALLOCATE ALL

Explicit transaction forwarding policy

In an explicit transaction, BEGIN is forwarded to both the primary node and read-only nodes simultaneously.

In an explicit transaction, the query statements preceding any query statements that cannot be executed on the read-only nodes (such as INSERT) will be sent to read-only nodes.

In an explicit transaction, any query statements that cannot be executed on read-only nodes (such as INSERT) will be sent to the primary node. All subsequent query statements will be sent to the primary node to ensure that SELECT immediately sees the results of INSERT. This action continues until the transaction is disabled or terminated.

Last updated: 2025.11.17 16:15:03