From: Tom Lane <tgl@sss.pgh.pa.us>
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: Ron <ronljohnsonjr@gmail.com>
Cc: pgsql-admin <pgsql-admin@lists.postgresql.org>
Subject: Re: What to watch out for when ALTERing NUMERIC(38,0) to BIGINT?
Date: Thu, 28 Jul 2022 11:26:39 -0400
Message-ID: <3421791.1659021999@sss.pgh.pa.us> (raw)
In-Reply-To: <CAKFQuwZ8su=VAeyNZ6Wj5cU1OoZLQB+B3iPWh49k2yjk4o4ujQ@mail.gmail.com>
References: <a4465ae0-574a-1727-fcdd-1dac49b874c0@gmail.com>
<CAKFQuwZ8su=VAeyNZ6Wj5cU1OoZLQB+B3iPWh49k2yjk4o4ujQ@mail.gmail.com>
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Thu, Jul 28, 2022 at 8:13 AM Ron <ronljohnsonjr@gmail.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.
regards, tom lane
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Subject: Re: What to watch out for when ALTERing NUMERIC(38,0) to BIGINT?
In-Reply-To: <3421791.1659021999@sss.pgh.pa.us>
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