#35015: Update MySQL migration documentation for Mysql 8
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Reporter: Nicolas Lupien | Owner: nobody
Type: Uncategorized | Status: new
Component: Documentation | Version: 5.0
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Description changed by Nicolas Lupien:
Old description:
> Now that Django dropped support for MySQL 5.7, I think the documentation
> is no longer valid.
>
> > MySQL lacks support for transactions around schema alteration
> operations, meaning that if a migration fails to apply you will have to
> manually unpick the changes in order to try again (it’s impossible to
> roll back to an earlier point).
> >
> > In addition, MySQL will fully rewrite tables for almost every schema
> operation and generally takes a time proportional to the number of rows
> in the table to add or remove columns. On slower hardware this can be
> worse than a minute per million rows - adding a few columns to a table
> with just a few million rows could lock your site up for over ten
> minutes.
> >
> > Finally, MySQL has relatively small limits on name lengths for columns,
> tables and indexes, as well as a limit on the combined size of all
> columns an index covers. This means that indexes that are possible on
> other backends will fail to be created under MySQL.
New description:
Now that Django dropped support for MySQL 5.7, I think the documentation
is no longer valid.
> MySQL lacks support for transactions around schema alteration
operations, meaning that if a migration fails to apply you will have to
manually unpick the changes in order to try again (it’s impossible to roll
back to an earlier point).
>
> In addition, MySQL will fully rewrite tables for almost every schema
operation and generally takes a time proportional to the number of rows in
the table to add or remove columns. On slower hardware this can be worse
than a minute per million rows - adding a few columns to a table with just
a few million rows could lock your site up for over ten minutes.
>
> Finally, MySQL has relatively small limits on name lengths for columns,
tables and indexes, as well as a limit on the combined size of all columns
an index covers. This means that indexes that are possible on other
backends will fail to be created under MySQL.
https://docs.djangoproject.com/en/5.0/topics/migrations/#mysql
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Ticket URL: <https://code.djangoproject.com/ticket/35015#comment:1>
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