From: Tom Lane <tgl@sss.pgh.pa.us>
To: junhkang91@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18384: It's not bug just question about documentation
In-reply-to: <18384-d9f97269de73f0fa@postgresql.org>
References: <18384-d9f97269de73f0fa@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Fri, 08 Mar 2024 06:00:16 +0000"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <794153.1709911706.1@sss.pgh.pa.us>
Date: Fri, 08 Mar 2024 10:28:26 -0500
Message-ID: <794154.1709911706@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/794154.1709911706%40sss.pgh.pa.us>
Precedence: bulk

PG Bug reporting form <noreply@postgresql.org> writes:
> "The internal transaction ID type xid is 32 bits wide and wraps around every
> 4 billion transactions."
> "it is necessary to vacuum every table in every database at least once every
> two billion transactions."

> why Postgresql needs to vacuum in every 2B transactions even though txid
> wraps on every 4 billion transactions (double time)?

Because an XID that's more than 2B transactions in the past will wrap
around and be seen as a bit less than 2B transactions in the future,
causing any rows bearing that XID to become invisible to current
transactions.

			regards, tom lane