Private strand flush not complete in oracle alert log

this message is not an error except that the gap between this message and next log allocation is large.

The message means some log in memory must be written to log file before going to next sequence.

check log usage:

set pagesize 6000
set linesize 600
col MEMBER format a50
select a.group#, lf.member, a.bytes/1024/1024 mb, a.status, a.archived
   from v$logfile lf, v$log a
   where a.group# = lf.group#
  order by 1, 2;


reference:
http://www.orafaq.com/forum/t/122199/0/