From: Peter Smith <smithpb2...@gmail.com> On Thu, Sep 10, 2020 at 7:16 PM tsunakawa.ta...@fujitsu.com > <tsunakawa.ta...@fujitsu.com> wrote: > > ALTER TABLE takes long time proportional to the amount of existing data, > while wal_level = none doesn't. > > Right, but if wal_level=none is considered OK for that table with > existing data, then why not just create the table UNLOGGED in the > first place? (or ALTER it to set UNLOGGED just one time and then leave > it as UNLOGGED).
The target tables sometimes receive updates (for data maintenance and/or correction). They don't want those updates to be lost due to the database server crash. Unlogged tables lose their entire contents during crash recovery. Please think like this: logging is is the norm, and unlogged operations are exceptions/hacks for some requirement of which the user wants to minimize the use. Regards Takayuki Tsunakawa
