Re: MySQL backup and consistency of database and dump file

--lock-tables is enabled by default for mysqldump.  --single-transaction
offers a way to get a consistent dump without locking tables, but the
tables have to support transactions (which InnoDB does and MyISAM does
not).  You should probably use --single-transaction if you can.

The mediawiki.org article you reference tries to ensure consistency by
having you set $wgReadOnly to prevent writes to the database (at least from
within MediaWiki core).  I'm not sure how much effect it actually has,
given that --lock-tables is enabled by default, but it's been on the page
for 15 years, so it must be right. :)


On Sat, Apr 1, 2023 at 1:20 AM Jeffrey Walton <[email protected]> wrote:

> Hi Everyone,
>
> We are trying to workaround failed backups due to
> https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/2003866 . We
> used to use --single-transaction, but the option now requires RELOAD
> or FLUSH_TABLES. We failed to enable the privileges for the mwuser.
>
> MediaWiki's backup documentation is at
> https://www.mediawiki.org/wiki/Manual:Backing_up_a_wiki . Here is the
> command MediaWiki recommends:
>
>     mysqldump -h hostname -u userid -p \
>         --default-character-set=whatever dbname > backup.sql
>
> But the article does not discuss how to ensure consistency for the
> database and dump file. For MySQL, that should be --single-transaction
> or --lock-tables. (If I am reading the MySQL documentation correctly).
>
> My question is, what should we use to ensure consistency of the dump file?
>
> --single-transaction or --lock-tables or something else?
>
> Jeff
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