Minor grammar improvements.

Author: robertmhaas

doc/src/sgml/wal.sgml

@@ -424,13 +424,13 @@
    linkend="guc-checkpoint-segments"> log segments, or every <xref
    linkend="guc-checkpoint-timeout"> seconds, whichever comes first.
    The default settings are 3 segments and 300 seconds (5 minutes), respectively.
-   In cases where there are little or no writes to the WAL, checkpoints will be
+   In cases where little or no WAL has been written, checkpoints will be
    skipped even if checkpoint_timeout has passed.  At least one new WAL segment
    must have been created before an automatic checkpoint occurs.  The time
    between checkpoints and when new WAL segments are created are not related
    in any other way.  If file-based WAL shipping is being used and you want to
-   bound how often files are sent to standby server, to reduce potential data
-   loss you should adjust archive_timeout parameter rather than the checkpoint
+   bound how often files are sent to standby server to reduce potential data
+   loss, you should adjust archive_timeout parameter rather than the checkpoint
    parameters.  It is also possible to force a checkpoint by using the SQL
    command <command>CHECKPOINT</command>.
   </para>