Subject: Re: FrozenTransactionId
To: pgsql-docs@postgresql.org
References: <575D7955.6060209@postgrespro.ru>
 <1473096445753-5919545.post@n3.nabble.com> <31833.1473097584@sss.pgh.pa.us>
 <57CDED18.8060005@postgrespro.ru>
From: Egor Rogov <e.rogov@postgrespro.ru>
Message-ID: <57CE6F15.4060101@postgrespro.ru>
Date: Tue, 6 Sep 2016 10:24:05 +0300
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Sorry, my last email went without the attachment.

On 06.09.2016 01:09, Egor Rogov wrote:
> Tom Lane <[hidden email] 
> </user/SendEmail.jtp?type=node&node=5919578&i=0>> writes:
> > It'd be more likely to get pushed if you'd submitted it in an easily
> > reviewable form, ie without reflowing the entire (rather long) 
> paragraph.
> > As-is, it's much too hard to see what you changed or didn't change.
> Please find another patch attached. I hope it is a bit easier to 
> review now.
>
> *maintenance-2.patch* (2K) Download Attachment 
> <http://postgresql.nabble.com/attachment/5919578/0/maintenance-2.patch>
>
Regards,
Egor Rogov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company


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    Sorry, my last email went without the attachment.<br>
    <br>
    <div class="moz-cite-prefix">On 06.09.2016 01:09, Egor Rogov wrote:<br>
    </div>
    <blockquote cite="mid:57CDED18.8060005@postgrespro.ru" type="cite">Tom
      Lane &lt;<a moz-do-not-send="true"
        href="/user/SendEmail.jtp?type=node&amp;node=5919578&amp;i=0"
        target="_top" rel="nofollow" link="external">[hidden email]</a>&gt;
      writes:
      <br>
      &gt; It'd be more likely to get pushed if you'd submitted it in an
      easily
      <br>
      &gt; reviewable form, ie without reflowing the entire (rather
      long) paragraph.
      <br>
      &gt; As-is, it's much too hard to see what you changed or didn't
      change.
      <br>
      Please find another patch attached. I hope it is a bit easier to
      review now.
      <br>
      <br>
      <div class="small"><img moz-do-not-send="true"
          src="http://postgresql.nabble.com/images/icon_attachment.gif">
        <strong>maintenance-2.patch</strong> (2K) <a
          moz-do-not-send="true"
href="http://postgresql.nabble.com/attachment/5919578/0/maintenance-2.patch"
          target="_top" rel="nofollow" link="external">Download
          Attachment</a></div>
      <!--end-attachments--><br>
    </blockquote>
    Regards,
    <br>
    Egor Rogov
    <br>
    Postgres Professional: <a moz-do-not-send="true"
      href="http://www.postgrespro.com" target="_top" rel="nofollow"
      link="external">http://www.postgrespro.com</a><br>
    The Russian Postgres Company
    <br>
    <div class="small"><br>
    </div>
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diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 2713883..7d1ee4e 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -406,26 +406,23 @@
 
    <para>
     The reason that periodic vacuuming solves the problem is that
-    <command>VACUUM</> will mark rows as <emphasis>frozen</>, indicating that
+    <command>VACUUM</> will mark rows as <emphasis>frozen</> (by setting appropriate hint bits), indicating that
     they were inserted by a transaction which committed sufficiently far in
     the past that the effects of the inserting transaction is certain to be
     visible, from an MVCC perspective, to all current and future transactions.
-    <productname>PostgreSQL</> reserves a special XID,
-    <literal>FrozenTransactionId</>, which does not follow the normal XID
-    comparison rules and is always considered older
-    than every normal XID. Normal XIDs are
+    Usually XIDs are
     compared using modulo-2<superscript>32</> arithmetic. This means
-    that for every normal XID, there are two billion XIDs that are
+    that for every XID, there are two billion XIDs that are
     <quote>older</> and two billion that are <quote>newer</>; another
-    way to say it is that the normal XID space is circular with no
+    way to say it is that the XID space is circular with no
     endpoint. Therefore, once a row version has been created with a particular
-    normal XID, the row version will appear to be <quote>in the past</> for
-    the next two billion transactions, no matter which normal XID we are
-    talking about. If the row version still exists after more than two billion
+    XID, the row version will appear to be <quote>in the past</> for
+    the next two billion transactions.
+    If the row version still exists after more than two billion
     transactions, it will suddenly appear to be in the future. To
-    prevent this, frozen row versions are treated as if the inserting XID were
-    <literal>FrozenTransactionId</>, so that they will appear to be
-    <quote>in the past</> to all normal transactions regardless of wraparound
+    prevent this, usual visibility rules are not applied to frozen row versions.
+    Instead they are considered to be
+    <quote>in the past</> to all transactions regardless of wraparound
     issues, and so such row versions will be valid until deleted, no matter
     how long that is.
    </para>

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