Question 193 of 1,446
PCDE Migrate data solutions Practice Question
A company is migrating an on-premises PostgreSQL 13 database to AlloyDB for PostgreSQL using DMS continuous migration. The source is configured with logical replication using the pglogical extension. During the initial sync, the migration job fails with the error 'could not open relation with OID xxxx'. What is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A DDL operation on the source dropped or altered a table after the replication slot was created.
DMS uses logical replication slots when possible. If the source has DDL changes (e.g., table dropped) after the slot is created, the replication slot may become invalid.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The source database has a firewall blocking the DMS IP address.
Why it's wrong here
Firewall issues typically cause connection timeouts, not relation OID errors.
- ✗
The source database does not have the pglogical extension installed.
Why it's wrong here
Missing extension would cause a different error about the extension itself.
- ✗
The target AlloyDB cluster does not have the pglogical extension.
Why it's wrong here
AlloyDB uses built-in logical replication; pglogical is not required on target.
- ✓
A DDL operation on the source dropped or altered a table after the replication slot was created.
Why this is correct
DDL changes invalidate the replication slot, causing the relation OID error.
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Last reviewed: Jul 4, 2026
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