[RFC] Add an until-0 loop in psql
От | Pierre Ducroquet |
---|---|
Тема | [RFC] Add an until-0 loop in psql |
Дата | |
Msg-id | 2654607.BC8G2H66zz@pierred-pdoc обсуждение исходный текст |
Ответы |
Re: [RFC] Add an until-0 loop in psql
Re: [RFC] Add an until-0 loop in psql |
Список | pgsql-hackers |
Hi When running database migrations with .sql files on a live database, it's not uncommon to have to run a migration in a loop to prevent a big lock on a table. For instance if one want to delete some old datas from a big table one would write : DELETE FROM big_table WHERE id IN (SELECT id FROM big_table WHERE bad = true LIMIT 1000); VACUUM big_table; Right now, doing this is quite inefficient. We either have to write a script in another language, or run psql in a shell loop and wait for the migration to stop altering rows. The attached **proof of concept** patch (I insist, it's a 15 minutes hack sprint with no previous knowledge of psql code) implements an 'until-0' loop in psql. The previous migration could be simply written as : \until-0 BEGIN; DELETE FROM big_table WHERE id IN (SELECT id FROM big_table WHERE bad = true LIMIT 1000); VACUUM big_table; COMMIT; \end-until And psql will execute it until there is no row affected in the inner queries. I am willing to write a proper patch for this (I hope the tell/seek is an acceptable implementation…), but I prefer having some feedback first. Thanks Pierre
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