Hi, Le lun. 25 janv. 2021 à 01:38, Demitri Muna <postgre...@demitri.com> a écrit :
> Hi, > > I would like to request a little clarification on the CLUSTER and VACUUM > commands. My use case here (partially) is when my disk runs out of space > and I want to move a table to a newly created tablespace. These questions > somewhat overlap. Let’s say I am starting with a table that is not > CLUSTERed on a given index, but I want it to be. > > * If I run “CLUSTER table USING idx” on a table, is VACUUM FULL > required/useful afterwards, or should I assume that the cluster operation > did the equivalent of a VACUUM FULL? > The cluster operation is a VACUUM FULL with a sort step, so you don't need a VACUUM FULL after a CLUSTER. > * If I have previously run a CLUSTER command on a table, will future > VACUUM FULL commands rewrite the table in the order specified in the > previous CLUSTER? > No, you still need CLUSTER. > * If I want to move a table to a new tablespace, is it possible to > CLUSTER+VACUUM in the same step since the whole table will be rewritten > anyway? This would be very useful in low-disk space scenarios. I did find > this answer, but it’s dated several years ago and was hoping for something > better supported. https://dba.stackexchange.com/a/87457/121020 No, but this is something being worked on. See https://commitfest.postgresql.org/31/2269/ for details. > The documentation is somewhat silent on these details, so I thought I’d > ask here. Right now I move a table to a new tablespace, cluster on an > index, and then do a full vacuum which results in three full copies of the > table being written, which seems less than optimal where one should only be > needed as far as I understand things. > > Cheers, > Demitri > >
