Re: [HACKERS] ALTER TABLE MODIFY COLUMN

[Hiroshi Inoue]

Mark Butler wrote: > > I was looking at how hard it would be to support altering column types and it > seems to me that it would be trivial to support changing nullability, Yes. The problem is how to formulate 'DROP CONSTRAINT' feature. > increasing the maximum length of the VARCHAR data type and increasing the > precision or scale of the DECIMAL / NUMERIC data type. > Yes. The problem is how PostgreSQL could recognize the fact. [snip] > I understand that with the current heap tuple format described in > backend/access/common.c that changing the type of any fixed length attribute > requires updating every row. > > Surely if we have an write exclusive table lock we can rewrite tuples in place > rather than creating new versions with its corresponding 2x space requirement. > PostgreSQL has a no overwrite storage manager, so this seems to have little advantage. We now have a mechanism to replace existent relation files safely. We could avoid running VACUUM, multiple version of tuples in a file etc ... regards, Hiroshi Inoue ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly