How to Convert Ordinary to Atomic

New, official way

• Implemented automatic conversion of database engine from Ordinary to Atomic (ClickHouse® Server 22.8+). Create empty convert_ordinary_to_atomic file in flags directory and all Ordinary databases will be converted automatically on next server start.
• The conversion is not automatic between upgrades, you need to set the flag as explained below:

Warnings:
 * Server has databases (for example `test`) with Ordinary engine, which was deprecated. To convert this database to the new Atomic engine, create a flag /var/lib/clickhouse/flags/convert_ordinary_to_atomic and make sure that ClickHouse has write permission for it.
Example: sudo touch '/var/lib/clickhouse/flags/convert_ordinary_to_atomic' && sudo chmod 666 '/var/lib/clickhouse/flags/convert_ordinary_to_atomic'

• Resolves #39546. #39933 (Alexander Tokmakov)

• There can be some problems if the default database is Ordinary and fails for some reason. You can add:

<clickhouse>
     <allow_reserved_database_name_tmp_convert>1</allow_reserved_database_name_tmp_convert>
</clickhouse>

More detailed info here