Error in ALTER TABLE documentation
От | Tom Lane |
---|---|
Тема | Error in ALTER TABLE documentation |
Дата | |
Msg-id | 4198.1439562761@sss.pgh.pa.us обсуждение исходный текст |
Список | pgsql-docs |
The Notes section of the ALTER TABLE reference page explains that ALTER DROP COLUMN doesn't immediately reclaim any space, and then says: To force an immediate rewrite of the table, you can use VACUUM FULL, CLUSTER or one of the forms of ALTER TABLE that forces a rewrite. This results in no semantically-visible change in the table, but gets rid of no-longer-useful data. Isn't this wrong in context? That is, yes the rewriting forms of ALTER TABLE would reclaim dead-column space, because they reconstruct every tuple. But VACUUM FULL and CLUSTER do not reconstruct tuples AFAIR, so they wouldn't do a thing to reclaim space from a dropped column. I think this reference to those two commands should be removed, and maybe tighten the description of what's being recommended, say like so: To force immediate reclamation of space occupied by a dropped column, you can execute one of the forms of ALTER TABLE that performs a rewrite of the whole table. This results in reconstructing each row with the dropped column replaced by a null value. regards, tom lane
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