Help Center/ Data Replication Service/ Troubleshooting/ Troubleshooting/ Failure Cases/ Real-Time Synchronization from PostgreSQL to PostgreSQL/ Incremental Synchronization Error: remaining connection slots are reserved
Updated on 2025-07-21 GMT+08:00
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Incremental Synchronization Error: remaining connection slots are reserved

Scenarios

During incremental synchronization, an error is reported, and the log information is as follows: service INCREMENT failed, cause by: Unable to connect to DBMS: url= %s user= %s, Caused by: FATAL: remaining connection slots are reserved for non-replication superuser connections.

Possible Causes

The number of user connections to the destination database reaches the upper limit. As a result, the connection to the destination database fails to be established.

Log in to the destination RDS PostgreSQL database and run the following SQL statement:

  • View max_connections. 
    show max_connections;
  • Check the current number of connections. 
    select count(*) from pg_stat_activity;

Solution

On the destination RDS PostgreSQL database console, change the value of max_connections to a larger value and make it take effect. Each DRS task requires about 100 connections.