Help Center/ Relational Database Service/ User Guide (Kuala Lumpur Region)/ Troubleshooting/ RDS for MySQL/ Performance Issues/ Read Replica Occupies Far More Storage Than the Primary Instance
Updated on 2025-10-28 GMT+08:00
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Read Replica Occupies Far More Storage Than the Primary Instance

Scenario

The storage usage of an RDS for MySQL read replica was 195 GB higher than that of the primary DB instance.

Troubleshooting

Check the transactions running on the read replica.

As shown in the preceding figure, a long transaction started one day ago and was not committed yet. The undo logs accumulated for almost a whole day and were not cleared. Therefore, the storage usage was high.

Solution

  • Method 1: Wait until the transaction is committed. After that, the undo logs will be cleared, releasing storage space.
  • Method 2: Kill the corresponding session to stop the long transaction.
Parent topic: Performance Issues