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From: Bruce Momjian <[email protected]>
To: Euler Taveira <[email protected]>
Cc: Kyotaro HORIGUCHI <[email protected]>
Cc: [email protected]
Subject: Re: Lifetime of commit timestamps
Date: Fri, 17 Nov 2023 16:01:27 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>

On Fri, Nov 17, 2023 at 03:39:14PM -0300, Euler Taveira wrote:
> On Mon, Nov 13, 2023, at 9:47 PM, Bruce Momjian wrote:
> 
>     Is this documentation change still relevant?
> 
> 
> I think so. AFAICS nothing changed. Unless you read the source code, it is not
> clear that VACUUM removes the information for frozen tuples. They are decoupled
> (but executed in the same routine for convenience), hence, someone can ask why
> the pg_xact_commit_timestamp() returns NULL for a transaction that was executed
> *after* you enable track_commit_timestamp. The answer is the design used a
> existing mechanism to clean up data in order to avoid creating a new one.

Okay, I have developed the attached patch based on Horiguchi-san's
version.

-- 
  Bruce Momjian  <[email protected]>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Only you can decide what is important to you.


Attachments:

  [text/x-diff] txtime.diff (574B, ../[email protected]/2-txtime.diff)
  download | inline diff:
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 93f068edcf..b311a11b33 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25978,7 +25978,8 @@ SELECT collation for ('foo' COLLATE "de_DE");
     They only provide useful data when the
     <xref linkend="guc-track-commit-timestamp"/> configuration option is
     enabled, and only for transactions that were committed after it was
-    enabled.
+    enabled.  The commit timestamps of frozen tuples are removed during
+    vacuum.
    </para>
 
    <table id="functions-commit-timestamp">

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