Azure postgre sql mirroring does not install cdc extension in one of the db

Question

Azure postgre sql mirroring does not install cdc extension in one of the db

Gediminas 20

Mirroring on the postgresql db does not install cdc extension which does not allow mirroring to be enabled

in default db named postgres it isntalls but in our other db it does not. Anyone have an idea why it can be like this ? We using the preview function and doing everythign what it says in microsoft learn

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Answer 1

Amira Bedhiafi 36,716 Volunteer Moderator

Hello Gediminas !

Thank you for posting on Microsoft Learn.

The CDC bit isn’t global as Fabric mirroring preview adds the azure_cdc extension per database, and only for the databases you select in the Azure portal mirroring enablement flow. If it shows up in postgres but not in your user DB, it usually means that DB wasn’t included (or your server doesn’t meet a preview limitation), so the extension wasn’t registered there.

On the same flexible server:

PostgreSQL version must be 14–17
Compute tier must not be burstable (GP/MO only)
High availability must be off.
No read replicas (and not a primary that has replicas).

If any of these are true, the mirroring workflow will skip registering azure_cdc in your DB. https://learn.microsoft.com/en-us/fabric/database/mirrored-database/azure-database-postgresql-limitations

You can rerun the mirroring enablement flow and include the right DB

In the Azure portal, go to your Azure Database for PostgreSQL Flexible Server under Fabric mirroring (preview) then Get started:

The page checks prerequisites and lets you select which databases to enable.
Select your user DB (not just postgres) then click prepare then accept the restart.

This flow preloads and registers azure_cdc only for the selected databases and bumps needed server params. https://learn.microsoft.com/en-us/azure/postgresql/flexible-server/concepts-fabric-mirroring

By default you can mirror up to 3 databases per server. If you need more, increase azure_cdc.max_fabric_mirrors on the server first, then rerun the flow.

https://learn.microsoft.com/en-us/azure/postgresql/flexible-server/concepts-fabric-mirroring

You can check if the extension is registered in that specific database:

-- Is the extension even available on the server?
SELECT * FROM pg_available_extensions WHERE name = 'azure_cdc';

-- Is it installed in THIS database?
SELECT * FROM pg_extension WHERE extname = 'azure_cdc';

-- Did the workflow set logical WAL?
SHOW wal_level;

If pg_extension returns no row for azure_cdc in your DB, it wasn’t registered there then go back to step 2.

Once installed, you’ll also see the azure_cdc schema and can use the troubleshooting UDFs like azure_cdc.tracked_publications() and azure_cdc.tracked_batches().

Gediminas 20 Reputation points

2025-08-26T01:59:44.24+00:00
I went through all the checks you suggested and can confirm the database requirements are satisfied:

PostgreSQL version: running within version 14.18.

Compute tier: not burstable.

High availability: disabled.

Replication: no read replicas configured, and the server is not acting as a primary with replicas.

I also tried re-enabling the mirroring flow and included the correct user database, but the azure_cdc extension still isn’t showing up there.
Swapnesh Panchal 5 Reputation points Microsoft External Staff Moderator

2025-08-26T10:16:24.1266667+00:00
Hi @Gediminas ,

It seems the azure_cdc extension installs fine in the default postgres database but not in your user database during mirroring setup—despite all requirements being met. That’s definitely odd.

Here are a few quick checks:

Database Selection: Ensure the user database was selected during the mirroring enablement flow.

Extension Availability: SQL:SELECT * FROM pg_available_extensions WHERE name = 'azure_cdc'; Show more lines

Extension Installed?: SQL:SELECT * FROM pg_extension WHERE extname = 'azure_cdc';

WAL Level: It should be logical or 1

Additional checks

Database Already Mirrored Elsewhere: If your user database is already mirrored in another Fabric workspace, it cannot be mirrored again.

Table Count Limit: Fabric mirroring supports up to 500 tables per database. If your database exceeds this, only the first 500 tables are mirrored.

Permission Issues: The database role used during mirroring must have explicit permissions for CDC setup.

If everything seems correct but the issue persists, it could point to a deeper underlying problem.

To help investigate further, could you please share the following:

Any errors encountered during the mirroring flow

The exact steps you followed

Any configuration differences between the user database and PostgreSQL

If you have any further questions, feel free to respond in this same thread.
Gediminas 20 Reputation points

2025-08-27T07:06:23.52+00:00

So the mirroring part has no error it says all good everything configured and ready for mirroring. But when you try mirror in fabric we get error :
Unable to retrieve list of tables from source server. 42883: function azure_cdc.is_table_mirrorable(information_schema.sql_identifier, information_schema.sql_identifier) does not exist POSITION: 278 Activity ID: e16260e1-fd41-4398-8223-ceae2edf2c94 Refresh or troubleshoot the issue.
Swapnesh Panchal 5 Reputation points Microsoft External Staff Moderator

2025-08-28T06:25:29.94+00:00
Hi Gediminas,
You’re seeing an error that the function azure_cdc.is_table_mirrorable (part of the Azure CDC extension) is missing in the user database, even though the mirroring setup reports “success.” This usually happens because:

The Azure CDC extension was installed only in the default postgres database and not in the specific user database selected for mirroring, or

The user database was silently skipped during mirroring due to unmet prerequisites or configuration gaps.

Step 1 — Verify the Extension in the Target (User) Database

Connect to the user database you intend to mirror, then run:

SELECT *

FROM pg_extension

WHERE extname = 'azure_cdc';

If this returns no rows, the Azure CDC extension is not installed in that database. (if possible, please share result of Quary)

*Optional function check (confirms the function’s presence in the expected schema):

SELECT
n.nspname AS schema_name,
p.proname AS function_name

FROM pg_proc p

JOIN pg_namespace n ON n.oid = p.pronamespace

WHERE n.nspname = 'azure_cdc'

AND p.proname = 'is_table_mirrorable';

Extensions are per‑database in PostgreSQL.
Confirm in both the default postgres DB and the user DB you’re mirroring.

Step 2 — Address Allow‑List / Preview Constraints

Even when prerequisites are met, installation can fail due to allow‑list restrictions or preview limitations for azure_cdc.

Try the following:

Re‑prepare the server: remove the database from mirroring and add it again, ensuring the user database is explicitly selected.

Step 3 — Re‑check Core Prerequisites (Source Server)

Ensure your PostgreSQL server and database meet Microsoft Fabric mirroring requirements:

PostgreSQL version: 14–17

Compute tier: Non‑burstable (e.g., avoid B‑series)

High Availability: Disabled

Replicas: No read replicas configured

Selection: The exact user database must be explicitly selected during mirroring setup (not just the server or default DB)

If any of these are not satisfied, the portal may silently skip extension registration in the user database.

Step 4 — Re‑run Mirroring Setup Carefully

Select the specific user database you need to mirror (double‑check the name).

Complete setup and wait for provisioning to finish.

Re‑run the queries in Step 1 against the user database to confirm azure_cdc and the is_table_mirrorable function exist.

if everything seems correct but the issue persists, we needed some more information for further troubleshooting please provide:

Error: Screenshots or exact error text or log

Steps: followed for configuring the user-defined database selected for mirroring

Source server details: Region, PostgreSQL version, tier/SKU, HA status, replicas.

Database details: query result for pg_extension.

Mirroring attempt details: region, portal flow, error messages, correlation IDs.

Configuration differences: Any variations from the default postgres DB (extensions, roles, schemas).

If you share the details above, I can validate the configuration and provide the exact next steps.
Gediminas 20 Reputation points

2025-08-29T12:25:30.87+00:00

I’ve repeated all the checks multiple times. The default database gets the CDC extension, but our database la-ssp-db-dev—with the same engine/version and configuration—does not.
Swapnesh Panchal 5 Reputation points Microsoft External Staff Moderator

2025-08-29T14:57:56.2466667+00:00

Hi Gediminas,

Please share the requested details with us. Providing more information will help us troubleshoot the issue effectively.

Steps: followed for configuring the user-defined database selected for mirroring
Error: Screenshots or exact error text or log
Source server details: PostgreSQL version, tier/SKU, HA status, replicas.
Database details: query result for pg_extension.
Mirroring attempt details: region, portal flow, error messages, correlation IDs.
Configuration differences: Any variations from the default postgres DB (extensions, roles, schemas).

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Azure postgre sql mirroring does not install cdc extension in one of the db

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