doc: Fix some grammar for logical decoding description and functions

This documentation is has been added for the support of logical decoding
on standbys.  Some markups were missing, hence add some where required.

Author: Thom Brown
Reviewed-by: Justin Pryzby, Daniel Gustafsson
Discussion: https://postgr.es/m/CAA-aLv7xCZ0nBJa-NWe0rxBB28TjFjS2JtjiZMoQ+0wsugG+hQ@mail.gmail.com

doc/src/sgml/func.sgml

@@ -27084,8 +27084,8 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
        </para>
        <para>
         Take a snapshot of running transactions and write it to WAL, without
-        having to wait bgwriter or checkpointer to log one. This is useful for
-        logical decoding on standby, as logical slot creation has to wait
+        having to wait for bgwriter or checkpointer to log one. This is useful
+        for logical decoding on standby, as logical slot creation has to wait
         until such a record is replayed on the standby.
        </para></entry>
       </row>

doc/src/sgml/logicaldecoding.sgml

@@ -321,16 +321,18 @@ postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NU
      <command>VACUUM</command> from removing required rows from the system
      catalogs, <varname>hot_standby_feedback</varname> should be set on the
      standby. In spite of that, if any required rows get removed, the slot gets
-     invalidated. It's highly recommended to use a physical slot between the primary
-     and the standby. Otherwise, hot_standby_feedback will work, but only while the
-     connection is alive (for example a node restart would break it). Then, the
-     primary may delete system catalog rows that could be needed by the logical
-     decoding on the standby (as it does not know about the catalog_xmin on the
-     standby). Existing logical slots on standby also get invalidated if wal_level
-     on primary is reduced to less than 'logical'. This is done as soon as the
-     standby detects such a change in the WAL stream. It means, that for walsenders
-     that are lagging (if any), some WAL records up to the wal_level parameter change
-     on the primary won't be decoded.
+     invalidated. It's highly recommended to use a physical slot between the
+     primary and the standby. Otherwise, <varname>hot_standby_feedback</varname>
+     will work but only while the connection is alive (for example a node
+     restart would break it). Then, the primary may delete system catalog rows
+     that could be needed by the logical decoding on the standby (as it does
+     not know about the catalog_xmin on the standby). Existing logical slots
+     on standby also get invalidated if <varname>wal_level</varname> on the
+     primary is reduced to less than <literal>logical</literal>.
+     This is done as soon as the standby detects such a change in the WAL stream.
+     It means that, for walsenders which are lagging (if any), some WAL records up
+     to the <varname>wal_level</varname> parameter change on the primary won't be
+     decoded.
     </para>
 
     <para>

doc/src/sgml/monitoring.sgml

@@ -4757,7 +4757,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </para>
       <para>
        Number of uses of logical slots in this database that have been
-       canceled due to old snapshots or a too low <xref linkend="guc-wal-level"/>
+       canceled due to old snapshots or too low a <xref linkend="guc-wal-level"/>
        on the primary
       </para></entry>
      </row>