--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 <noloader@gmail.com> 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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