PCDE Migrate data solutions Practice Question
A team is migrating an on-premises PostgreSQL 13 database to AlloyDB using DMS continuous migration. During the CDC phase, the migration job shows an error: 'ERROR: could not start WAL streaming: ERROR: replication slots are not enabled on the source.' The source is running in Google Cloud Compute Engine. 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
✓
The source database parameter wal_level is set to 'replica' instead of 'logical'.
DMS continuous migration for PostgreSQL requires logical replication, which uses replication slots. The error indicates that the source database does not have the necessary configuration to support replication slots (wal_level=logical, max_replication_slots > 0).
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 DMS connection profile uses the wrong public IP.
Why it's wrong here
Connectivity issues would show a different error (e.g., connection timeout).
- ✗
The source database is in read-only mode.
Why it's wrong here
Read-only does not prevent WAL streaming, but would cause other issues.
- ✗
The source database does not have the pglogical extension installed.
Why it's wrong here
pglogical is an alternative, but DMS uses built-in logical replication, not pglogical.
- ✓
The source database parameter wal_level is set to 'replica' instead of 'logical'.
Why this is correct
wal_level must be set to 'logical' to enable logical replication slots.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDE exam.