doc: mention vacuum's removal of commit timestamp information

Reported-by: Kyotaro HORIGUCHI Discussion: https://postgr.es/m/20180622.172132.230342845.horiguchi.kyotaro@lab.ntt.co.jp Co-authored-by: Kyotaro HORIGUCHI Backpatch-through: 16
2 years ago · c136eb0298
parent 7471230cc6
commit c136eb0298
1 changed files with 2 additions and 1 deletions
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@ -25704,7 +25704,8 @@ 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.  Commit timestamp information is routinely removed during
+    vacuum.
   </para>

   <table id="functions-commit-timestamp">