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mysql: create database with explicit UTF-8 character set and collation
A spin-off from Issue #378.
In MySQL, the character sets for server, database, tables, and connection are
set independently. Ideally, they should all use UTF-8, but systems tend to use
latin1 as default encoding, for example:
character_set_server = latin1
collation_server = latin1_swedish_ci
Databases would thus by default be created as:
character_set_database = latin1
collation_database = latin1_swedish_ci
To make things work consistently anyway, we have so far specified the utf8mb4
charset explicitly when creating tables, but there is no corresponding simple
option for specifying the collation for tables. We need a better solution.
If necessary and possible, the system charset and collation should be set to
UTF-8. Some systems already have these defaults default - see
https://mariadb.com/kb/en/differences-in-mariadb-in-debian-and-ubuntu/ .
The defaults can be changed as described on
https://mariadb.com/kb/en/setting-character-sets-and-collations/#example-changing-the-default-character-set-to-utf-8
to give something like:
character_set_server = utf8mb4
collation_server = utf8mb4_unicode_ci
Databases will then by default be created as:
character_set_database = utf8mb4
collation_database = utf8mb4_unicode_ci
and there is thus no longer any need for specifying the charset when creating
tables.
To be reasonably resilient across all systems without relying on system
defaults, we will now start specifying the charset and collation when creating
the database, but drop the specification of charset when creating tables.
For existing databases, it is recommended to change encoding (and collation) by
altering the database and each of the tables inside it as described on
https://stackoverflow.com/questions/6115612/how-to-convert-an-entire-mysql-database-characterset-and-collation-to-utf-8 .
Note the use of utf8mb4_unicode_ci instead of utf8mb4_general_ci - see
https://stackoverflow.com/questions/766809/whats-the-difference-between-utf8-general-ci-and-utf8-unicode-ci .
For investigation of these issues, consider the output from:
show variables like '%char%';
show variables like '%collation%';
show create database `KALLITHEA_DB_NAME`;
SELECT * FROM information_schema.SCHEMATA WHERE schema_name = "KALLITHEA_DB_NAME";
SELECT * FROM information_schema.TABLES T, information_schema.COLLATION_CHARACTER_SET_APPLICABILITY CCSA WHERE CCSA.collation_name = T.table_collation AND T.table_schema = "KALLITHEA_DB_NAME";
A spin-off from Issue #378.
In MySQL, the character sets for server, database, tables, and connection are
set independently. Ideally, they should all use UTF-8, but systems tend to use
latin1 as default encoding, for example:
character_set_server = latin1
collation_server = latin1_swedish_ci
Databases would thus by default be created as:
character_set_database = latin1
collation_database = latin1_swedish_ci
To make things work consistently anyway, we have so far specified the utf8mb4
charset explicitly when creating tables, but there is no corresponding simple
option for specifying the collation for tables. We need a better solution.
If necessary and possible, the system charset and collation should be set to
UTF-8. Some systems already have these defaults default - see
https://mariadb.com/kb/en/differences-in-mariadb-in-debian-and-ubuntu/ .
The defaults can be changed as described on
https://mariadb.com/kb/en/setting-character-sets-and-collations/#example-changing-the-default-character-set-to-utf-8
to give something like:
character_set_server = utf8mb4
collation_server = utf8mb4_unicode_ci
Databases will then by default be created as:
character_set_database = utf8mb4
collation_database = utf8mb4_unicode_ci
and there is thus no longer any need for specifying the charset when creating
tables.
To be reasonably resilient across all systems without relying on system
defaults, we will now start specifying the charset and collation when creating
the database, but drop the specification of charset when creating tables.
For existing databases, it is recommended to change encoding (and collation) by
altering the database and each of the tables inside it as described on
https://stackoverflow.com/questions/6115612/how-to-convert-an-entire-mysql-database-characterset-and-collation-to-utf-8 .
Note the use of utf8mb4_unicode_ci instead of utf8mb4_general_ci - see
https://stackoverflow.com/questions/766809/whats-the-difference-between-utf8-general-ci-and-utf8-unicode-ci .
For investigation of these issues, consider the output from:
show variables like '%char%';
show variables like '%collation%';
show create database `KALLITHEA_DB_NAME`;
SELECT * FROM information_schema.SCHEMATA WHERE schema_name = "KALLITHEA_DB_NAME";
SELECT * FROM information_schema.TABLES T, information_schema.COLLATION_CHARACTER_SET_APPLICABILITY CCSA WHERE CCSA.collation_name = T.table_collation AND T.table_schema = "KALLITHEA_DB_NAME";
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Database schema changes
=======================
Kallithea uses Alembic for :ref:`database migrations <upgrade_db>`
(upgrades and downgrades).
If you are developing a Kallithea feature that requires database schema
changes, you should make a matching Alembic database migration script:
1. :ref:`Create a Kallithea configuration and database <setup>` for testing
the migration script, or use existing ``development.ini`` setup.
Ensure that this database is up to date with the latest database
schema *before* the changes you're currently developing. (Do not
create the database while your new schema changes are applied.)
2. Create a separate throwaway configuration for iterating on the actual
database changes::
kallithea-cli config-create temp.ini
Edit the file to change database settings. SQLite is typically fine,
but make sure to change the path to e.g. ``temp.db``, to avoid
clobbering any existing database file.
3. Make your code changes (including database schema changes in ``db.py``).
4. After every database schema change, recreate the throwaway database
to test the changes::
rm temp.db
kallithea-cli db-create -c temp.ini --repos=/var/repos --user=doe --email doe@example.com --password=123456 --no-public-access --force-yes
kallithea-cli repo-scan -c temp.ini
5. Once satisfied with the schema changes, auto-generate a draft Alembic
script using the development database that has *not* been upgraded.
(The generated script will upgrade the database to match the code.)
::
alembic -c development.ini revision -m "area: add cool feature" --autogenerate
6. Edit the script to clean it up and fix any problems.
Note that for changes that simply add columns, it may be appropriate
to not remove them in the downgrade script (and instead do nothing),
to avoid the loss of data. Unknown columns will simply be ignored by
Kallithea versions predating your changes.
7. Run ``alembic -c development.ini upgrade head`` to apply changes to
the (non-throwaway) database, and test the upgrade script. Also test
downgrades.
The included ``development.ini`` has full SQL logging enabled. If
you're using another configuration file, you may want to enable it
by setting ``level = DEBUG`` in section ``[handler_console_sql]``.
The Alembic migration script should be committed in the same revision as
the database schema (``db.py``) changes.
See the `Alembic documentation`__ for more information, in particular
the tutorial and the section about auto-generating migration scripts.
.. __: http://alembic.zzzcomputing.com/en/latest/
Troubleshooting
---------------
* If ``alembic --autogenerate`` responds "Target database is not up to
date", you need to either first use Alembic to upgrade the database
to the most recent version (before your changes), or recreate the
database from scratch (without your schema changes applied).
|