On 7/28/22 10:26, Tom Lane wrote:
"David G. Johnston" <david.g.johnston@xxxxxxxxx> writes:
On Thu, Jul 28, 2022 at 8:13 AM Ron <ronljohnsonjr@xxxxxxxxx> wrote:
Besides what's mentioned in
https://www.postgresql.org/docs/12/ddl-alter.html#id-1.5.4.8.10, what
happens *internally* when I run:
ALTER TABLE foo ALTER COLUMN bar TYPE BIGINT;
IIUC, that would be the silver lining in all of this - the rewritten table
would have zero fragmentation and bloat.
Yeah. What happens internally is a table rewrite: the entire content
of the table (and its indexes) is written into a new set of files.
At commit, the old files are deleted. The main gotchas, for a large
table, are the transient disk space consumption and the fact that the
table stays exclusively locked the whole time.
Rewriting a 3TB table doesn't seem appetizing. Fortunately, there's only
one table like that...
--
Angular momentum makes the world go 'round.
