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db_schema_guide.md

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How to modify the database schema

CodeChecker is developed in rolling release model so it is important to update the database schema in a backward compatible way. This is achieved using the Alembic database migration tool.

CodeChecker uses SQLAlchemy for database operations. Please read SQLAlchemy declarative syntax documentation for syntax and semantics.

Alembic can compare the table metadata against the status of a database and based on this comparison it generates the migration script. Even though this method has it's limitations , in most cases it works well.

Updating configuration database schema

Config database schema scripts can be found under the config_db_migrate directory.

Automatic migration script generation (Online)

A Codechecker server should be started with the previous database schema version.

Step 1: Update the database model

The configuration database schema file can be found here: libcodechecker/server/config_db_model.py

Step 2: Check the alembic.ini configuration settings

Database connection should point to the correct database. Edit the sqlalchemy.url option in alembic.ini according to your database configuration.

Step 3: Use alembic to autogenerate migration scripts

alembic --name config_db revision --autogenerate -m "Change description"

Step 4: Check the generated scripts

The new migration script config_db_migrate/versions/{hash}_change_description.py is generated. You must always check the generated script because sometimes it isn't correct.

Step 5: Run all test cases.

All tests must pass!

Step 6: Commit the new version files.

Don't forget to commit the migration script with your other changes.

Updating the run database

Automatic migration script generation (Online)

A Codechecker server should be started and a product should be configured with a previous database schema version.

Step 1: Update the database model

The run database schema file can be found here: libcodechecker/server/run_db_model.py

Step 2: Check alembic.ini configuration

Database connection should point to the correct database. Edit the sqlalchemy.url option in alembic.ini according to your database configuration.

Step 2: Generating migration scripts using autogenerate

alembic --name run_db revision --autogenerate -m "Change description"

Step 3: Check the generated scripts

The new migration script db_migrate/versions/{hash}_change_description.py is generated. You must always check the generated script because sometimes it isn't correct.

Step 4: Run all test cases.

All tests must pass!

Step 5: Commit the new version files.

Don't forget to commit the migration script with your other changes.

Writing migration scripts by hand

Navigate to the root directory of CodeChecker source code and create an empty migration script using alembic revision:

alembic --name run_db revision -m "Change description"

The new file db_migrate/versions/{hash}_change_description.py is generated. This file contains an empty upgrade and a downgrade function.

The empty upgrade and downgrade should be written by hand.

Database upgrade for running servers

It is possible that a new release introduces database changes and database schema migration is required.

There are two database types which might need schema migration. One of them is the configuration database (storing product configurations) and the other is the run database (storing analysis reports).

If there is some schema mismatch and migration is needed you will get a warning at server start.

IMPORTANT before schema upgrade

If there is some schema change it is recommended to create a full backup of your configuration and run databases before running the migration. If there is some error during the migration you can still restore the previous version and there will be no data loss.

Migration at server start

Schema migration can be done at server start. The database for the config and product databases will be automatically checked. If there are databases which can be upgraded you will be asked if you want to upgrade the schema to the latest version.

NOTE: Before running the migration you should make a full backup of your config and product databases!

The config database location will be printed first at the server start. Migration of the config database is done independently from the product databases. The product database locations can be viewed with the CodeChecker server --db-status all command.

Checking if migration will be required.

Running the CodeChecker server --db-status all command with the new CodeChecker release will show you if database upgrade is needed for the new release.

NOTE: Use the same arguments which were used to start the server to check the status. It is required to find the used configuration database.

$ CodeChecker server --db-status all
[15:01] - Checking configuration database ...
[15:01] - Database is OK.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Product endpoint | Database status                                | Database location              | Schema version in the database | Schema version in the package
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Default          | Database is up to date.                        | ~/.codechecker/Default.sqlite  | 82ca43f05c10 (up to date)      | 82ca43f05c10
Default2         | Database schema mismatch! Possible to upgrade. | ~/.codechecker/Default2.sqlite | 82ca43f05c10                   | f1f7600168dc
-------------------------------------------------------------------------------------------------------------------------------------------------------------------

Upgrade configuration database

The configuration database migration can be done at server start. A prompt will ask you if you want to proceed with the schema upgrade.

NOTE: After the configuration database was upgraded only the newer CodeChecker releases will be able to read up the configuration. The older versions will fail to start.

Upgrade product databases

Check if migration is possible

With the CodeChecker server --db-status all the database statuses for all of the product databases can be checked.

Product migration

Schema upgrade can be done for each product independently or in a row for all of the products with the CodeChecker server --db-upgrade-schema PRODUCT_NAME command.

$ CodeChecker server --db-upgrade-schema Default
[15:01] - Checking configuration database ...
[15:01] - Database is OK.
[15:01] - Preparing schema upgrade for Default
[WARNING] [15:01] - Please note after migration only newer CodeChecker versions can be used to start the server
[WARNING] [15:01] - It is advised to make a full backup of your run databases.
[15:01] - ========================
[15:01] - Upgrading: Default
[15:01] - Database schema mismatch: migration is available.
Do you want to upgrade to new schema? Y(es)/n(o) y
Upgrading schema ...
Done.
Database is OK.
[15:01] - ========================

Schema upgrade can be done for multiple products in a row if the CodeChecker server --db-upgrade-schema all command is used. A prompt will ask for user input for each product, no schema modification is done without asking the user.

Further reading

You should also read the Alembic tutorial and the Operation Reference for details.