Hello,
In case you haven't done any changes on database schema of mediawiki core,
let me explain the process to you (if you know this, feel free to skip this
paragraph):
* Mediawiki core supports three types of RDBMS: MySQL, Sqlite, Postgres. It
used to be five (plus Oracle and MSSQL)
* For each one of these types, you need to do three parts: 1- Change the
tables.sql file so new installations get the new schema 2- Make .sql schema
change file, like an "ALTER TABLE" for current installations so they can
upgrade. 3- Wire that schema change file into *Updater.php file.
* For example, this is a patch to drop a column:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/473601 This file touches
14 different files, adds 94 lines and removes 30.
This is bad for several reasons:
* It is extremely complicated to do a even a simple schema change. Usually
something as simple as adding an column takes a whole day for me. There are
lots of complicating factors, like Sqlite doesn't have ALTER TABLE, so when
you want to make a patch for adding a column, you need to make a temporary
table with the new column, copy the old table data to it, drop the old
table and then rename the old table.
** Imagine the pain and sorrow when you want to normalize a table meaning
you need to do several schema changes: 1- Add a table, 2- Add a column on
the old table, 3- make the column not-nullable when it's filled and make
the old column nullable instead 4- drop the old column.
* It's almost impossible to test all DBMS types, I don't have MSSQL or
Oracle installed and I don't even know their differences with MySQL. I
assume most other developers are good in one type, not all.
* Writing raw sqls, specially duplicated ones, and doubly specially when we
don't have CI to test (because we won't install propriety software in our
infra) is pretty much prone to error. My favourite one was that a new
column on a table was actually added to the wrong table in MSSQL and it
went unnoticed for two years (four releases, including one LTS).
* It's impossible to support more DBMS types through extensions or other
third party systems. Because the maintainer needs to keep up with all
patches we add to core and write their equivalents.
* For lots of reasons, these schemas are diverging, there have been several
work to just reduce this to a minimum.
There was a RFC to introduce abstract schema and schema changes and it got
accepted and I have been working to implement this:
https://phabricator.wikimedia.org/T191231
This is not a small task, and like any big work, it's important to cut it
to small pieces and gradually improve things. So my plan is first, I
abstract the schema (tables.sql files), then slowly I abstract schema
changes. For now, the plan is to make these .sql files automatically
generated through maintenance scripts. So we will have a file called
tables.json and when running something like:
php maintenance/generateSchemaSql.php --json maintenance/tables.json --sql
maintenance/tables-generated.sql --type=mysql
It would produce tables-generated.sql file. The code that produces it is
Doctrine DBAL and this is already installed as a dev dependency of core
because you would need Doctrine if you want to make a schema change, if you
maintain an instance, you should not need anything. Most of the work for
automatically generating schema is already merged and the last part that
wires it (and migrates two tables) is up for review:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/595240
My request is that I need to make lots of patches and since I'm doing this
in my volunteer capacity, I need developers to review (and potentially help
with the work if you're excited about this like me). Let me know if you're
willing to be added in future patches and the current patch also welcomes
any feedback: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/595240
I have added the documentation in
https://www.mediawiki.org/wiki/Manual:Schema_changes for the plan and
future changes. The ideal goal is that when you want to do a schema change,
you just change tables.json and create a json file that is snapshot of
before and after table (remember, sqlite doesn't have alter table, meaning
it has to know the whole table). Also, once we are in a good shape in
migrating mediawiki core, we can start cleaning up extensions.
Any feedback is also welcome.
Best
--
Amir (he/him)
_______________________________________________
MediaWiki-l mailing list
To unsubscribe, go to:
https://lists.wikimedia.org/mailman/listinfo/mediawiki-l
In case you haven't done any changes on database schema of mediawiki core,
let me explain the process to you (if you know this, feel free to skip this
paragraph):
* Mediawiki core supports three types of RDBMS: MySQL, Sqlite, Postgres. It
used to be five (plus Oracle and MSSQL)
* For each one of these types, you need to do three parts: 1- Change the
tables.sql file so new installations get the new schema 2- Make .sql schema
change file, like an "ALTER TABLE" for current installations so they can
upgrade. 3- Wire that schema change file into *Updater.php file.
* For example, this is a patch to drop a column:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/473601 This file touches
14 different files, adds 94 lines and removes 30.
This is bad for several reasons:
* It is extremely complicated to do a even a simple schema change. Usually
something as simple as adding an column takes a whole day for me. There are
lots of complicating factors, like Sqlite doesn't have ALTER TABLE, so when
you want to make a patch for adding a column, you need to make a temporary
table with the new column, copy the old table data to it, drop the old
table and then rename the old table.
** Imagine the pain and sorrow when you want to normalize a table meaning
you need to do several schema changes: 1- Add a table, 2- Add a column on
the old table, 3- make the column not-nullable when it's filled and make
the old column nullable instead 4- drop the old column.
* It's almost impossible to test all DBMS types, I don't have MSSQL or
Oracle installed and I don't even know their differences with MySQL. I
assume most other developers are good in one type, not all.
* Writing raw sqls, specially duplicated ones, and doubly specially when we
don't have CI to test (because we won't install propriety software in our
infra) is pretty much prone to error. My favourite one was that a new
column on a table was actually added to the wrong table in MSSQL and it
went unnoticed for two years (four releases, including one LTS).
* It's impossible to support more DBMS types through extensions or other
third party systems. Because the maintainer needs to keep up with all
patches we add to core and write their equivalents.
* For lots of reasons, these schemas are diverging, there have been several
work to just reduce this to a minimum.
There was a RFC to introduce abstract schema and schema changes and it got
accepted and I have been working to implement this:
https://phabricator.wikimedia.org/T191231
This is not a small task, and like any big work, it's important to cut it
to small pieces and gradually improve things. So my plan is first, I
abstract the schema (tables.sql files), then slowly I abstract schema
changes. For now, the plan is to make these .sql files automatically
generated through maintenance scripts. So we will have a file called
tables.json and when running something like:
php maintenance/generateSchemaSql.php --json maintenance/tables.json --sql
maintenance/tables-generated.sql --type=mysql
It would produce tables-generated.sql file. The code that produces it is
Doctrine DBAL and this is already installed as a dev dependency of core
because you would need Doctrine if you want to make a schema change, if you
maintain an instance, you should not need anything. Most of the work for
automatically generating schema is already merged and the last part that
wires it (and migrates two tables) is up for review:
https://gerrit.wikimedia.org/r/c/mediawiki/core/+/595240
My request is that I need to make lots of patches and since I'm doing this
in my volunteer capacity, I need developers to review (and potentially help
with the work if you're excited about this like me). Let me know if you're
willing to be added in future patches and the current patch also welcomes
any feedback: https://gerrit.wikimedia.org/r/c/mediawiki/core/+/595240
I have added the documentation in
https://www.mediawiki.org/wiki/Manual:Schema_changes for the plan and
future changes. The ideal goal is that when you want to do a schema change,
you just change tables.json and create a json file that is snapshot of
before and after table (remember, sqlite doesn't have alter table, meaning
it has to know the whole table). Also, once we are in a good shape in
migrating mediawiki core, we can start cleaning up extensions.
Any feedback is also welcome.
Best
--
Amir (he/him)
_______________________________________________
MediaWiki-l mailing list
To unsubscribe, go to:
https://lists.wikimedia.org/mailman/listinfo/mediawiki-l