Migrate your database from PostgreSQL Single Server to PostgreSQL Flexible Server using Azure DMS

by | Jan 26, 2021 | Technology | 0 comments

This article is contributed. See the original author and article here.

Overview:


Azure Database for PostgreSQL recently announced Flexible Server,  Flexible Server is a new deployment option for Azure Database for PostgreSQL that gives you the control you need with multiple configuration parameters for fine-grained database tuning along with a simpler developer experience to accelerate end-to-end deployment. With Flexible Server, you will also have a new way to optimize cost with stop/start capabilities. 


 


In this article, we will provide a guideline on how to migrate your database from PostgreSQL Single Server to PostgreSQL Flexible Server using Azure DMS.


 


Important – Azure Database for PostgreSQL – Flexible Server is still in preview as of Jan 2021.


 


1 – Prepare the Source – Azure PostgreSQL – Single Server


 


You will need to set some Postgresql Parameters on the source as follows:


 


— parameter wal_level should be logical, on Azure PgSQL this can be done from Azure Portal as shown blow:


 


Ahmed_S_Mahmoud_0-1611574758260.png


 


— max_replication_slots = [number of slots], recommend setting to 5 slots
— max_wal_senders =[number of concurrent tasks] – The max_wal_senders parameter sets the number of concurrent tasks that can run, recommend setting to 10 tasks


 


2- Prepare the target for the migration – Flexible Server


 


You will need to migrate database schema from source to target using commands:


 


— on the source, create a schema dump file for a database


 


 


 

pg_dump -o -h hostname -U db_username -d db_name -s > your_schema.sql

 


 


 


 


— Import the schema into the target database


 


 


 

psql -h hostname -U db_username -d db_name < your_schema.sql

 


 


 


 


— Remove foreign keys in schema at target Azure Database for PostgreSQL


 


 


 

SELECT Q.table_name
    ,CONCAT('ALTER TABLE ', table_schema, '.', table_name, STRING_AGG(DISTINCT CONCAT(' DROP CONSTRAINT ', foreignkey), ','), ';') as DropQuery
        ,CONCAT('ALTER TABLE ', table_schema, '.', table_name, STRING_AGG(DISTINCT CONCAT(' ADD CONSTRAINT ', foreignkey, ' FOREIGN KEY (', column_name, ')', ' REFERENCES ', foreign_table_schema, '.', foreign_table_name, '(', foreign_column_name, ')' ), ','), ';') as AddQuery
FROM
    (SELECT
    S.table_schema,
    S.foreignkey,
    S.table_name,
    STRING_AGG(DISTINCT S.column_name, ',') AS column_name,
    S.foreign_table_schema,
    S.foreign_table_name,
    STRING_AGG(DISTINCT S.foreign_column_name, ',') AS foreign_column_name
FROM
    (SELECT DISTINCT
    tc.table_schema,
    tc.constraint_name AS foreignkey,
    tc.table_name,
    kcu.column_name,
    ccu.table_schema AS foreign_table_schema,
    ccu.table_name AS foreign_table_name,
    ccu.column_name AS foreign_column_name
    FROM information_schema.table_constraints AS tc
    JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name AND tc.table_schema = kcu.table_schema
    JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name AND ccu.table_schema = tc.table_schema
WHERE constraint_type = 'FOREIGN KEY'
    ) S
    GROUP BY S.table_schema, S.foreignkey, S.table_name, S.foreign_table_schema, S.foreign_table_name
    ) Q
    GROUP BY Q.table_schema, Q.table_name;

 


 


 


 


— Disable triggers at target Azure Database for PostgreSQL


 


 


 

SELECT DISTINCT CONCAT('ALTER TABLE ', event_object_schema, '.', event_object_table, ' DISABLE TRIGGER ', trigger_name, ';')
FROM information_schema.triggers

 


 


 


 


— Provision Database Migration Service and create a migration task


More details in Tutorial: Migrate PostgreSQL to Azure Database for PostgreSQL online via the Azure CLI – Azure Database Migration Service | Microsoft Docs


 


3 – Create Migration Project


 


You will need to use your Postgresql as source and provide the single server endpoint and credentials 


 


Ahmed_S_Mahmoud_1-1611574758268.png


 


Note:- You will need to make sure the connectivity between the source single server and DMS service on side and the DMS service and the target flexible server another side.


 


Details steps: Tutorial: Migrate PostgreSQL to Azure DB for PostgreSQL online via the Azure portal – Azure Database Migration Service | Microsoft Docs


 


4- Monitoring the migration project progress and you can perform the migration once it’s ready for cutover


 


Ahmed_S_Mahmoud_2-1611574758296.png


 


Ahmed_S_Mahmoud_3-1611574758312.png


 


Note:- After migration is complete, you might need to re-enable the triggers and create foreign keys. 


 


I hope you find this article helpful. If you have any feedback please do not hesitate to provide it in the comment section below.


 


Ahmed S. Mazrouh

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