“No space left on device” while AWS RDS Storage Auto Scaling Enabled

PostgreSQL RDS instance got “No space left on device” errors, even RDS storage auto scaling enabled. The storage can only be extended after at least 6 hours.

As for now,  although automatic scaling helps you to increase storage on your RDS instance dynamically, you should still configure the initial storage for your DB instance to an appropriate size for your typical workload.

Auto Scaling will kick in when these factors apply:

  • Free available space is less than 10 percent of the allocated storage.
  • The low-storage condition lasts at least five minutes.

We can also see, that the minimum the storage will increase is either 5GB or max 10% of your current allocated storage. That means that if you have an instance of 200Gb storage right now, your max ‘auto allocated’ storage space would be +20Gb of 200Gb which would be 220Gb. This will not be able to change for at least 6 hours.

Remember 6 hours policy when using “auto scaling”.

AWS DMS Validation Pending for Some Tables

While running an AWS DMS task for migrating on-premise Oracle to AWS PostgreSQL RDS, some tables records are fully loaded into target database. From Table Statistics, it shows some tables validations are pending forever without progressing at all.

Check “Migration task logs”, it just says :

[TASK_MANAGER]I:All tables are loaded.waiting for validation to finish... 
                                     (replicationtask.c:1234)

RESOLUTION

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Mismatched Records from AWS Database Migration Service Validation

Some times we see “Mismatched records” from AWS DMS validation. 

To check what records are mismatching between Source and Target database.

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Create a New AWS DB Parameter / Option Group

1)Create a new Parameter group:

2)Create a Option group:

3) Modify the customised parameter group and option group to meet your needs.

4)Create RDS instances by using new created parameter / option group.

aws dms table error

AWS DMS ( Data Migration Service ) task has been running for many hours, then failed with error “Table error” for Load State.

1)Check target database,  99% records have been migrated from Oracle source database to PostgreSQL RDS.

2)Check task log with bellow error:

00:04:00 2018-10-01T00:04:00 [SOURCE_UNLOAD ]E: ORA-01555: 
snapshot too old: rollback segment number 918 with name 
"_SYSSMU918_239767949$" too small [1020436] (oracle_endpoint_unload.c:226)

SOLUTION

Add more space to UNDO tablespace, and/or increase the value of parameter “undo_retention” for source Oracle database.