Re: What to watch out for when ALTERing NUMERIC(38,0) to BIGINT?

On 7/28/22 10:26, Tom Lane wrote:
> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
>> On Thu, Jul 28, 2022 at 8:13 AM Ron <ronljohnsonjr(at)gmail(dot)com> 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.