Add description about LogicalRewriteTruncate wait event into document.

MasaoFujii · MasaoFujii · commit 1beab076cefe · 2020-02-17T15:39:48.000+09:00
Back-patch to v10 where commit 249cf07 introduced LogicalRewriteTruncate wait event. Author: Fujii Masao Reviewed-by: Michael Paquier Discussion: https://postgr.es/m/949931aa-4ed4-d867-a7b5-de9c02b2292b@oss.nttdata.com
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
@@ -1341,7 +1341,7 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry>Waiting to apply WAL at recovery because it is delayed.</entry>
         </row>
         <row>
-         <entry morerows="65"><literal>IO</></entry>
+         <entry morerows="66"><literal>IO</></entry>
          <entry><literal>BufFileRead</></entry>
          <entry>Waiting for a read from a buffered file.</entry>
         </row>
@@ -1457,6 +1457,10 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry><literal>LogicalRewriteSync</></entry>
          <entry>Waiting for logical rewrite mappings to reach stable storage.</entry>
         </row>
+        <row>
+         <entry><literal>LogicalRewriteTruncate</></entry>
+         <entry>Waiting for truncate of mapping data during a logical rewrite.</entry>
+        </row>
         <row>
          <entry><literal>LogicalRewriteWrite</></entry>
          <entry>Waiting for a write of logical rewrite mappings.</entry>
