Database Monitoring Script

Total Size of Database with free space:
Select round(sum(used.bytes) / 1024 / 1024/1024 ) || ' GB' "Database Size",round(free.p / 1024 / 1024/1024) || ' GB' "Free space"
from (select bytes from v$datafile
      union all
      select bytes from v$tempfile
      union all
      select bytes from v$log) used, (select sum(bytes) as p from dba_free_space) free group by free.p;

Track Tablespace Used/Free Space:
SELECT /* + RULE */  df.tablespace_name "Tablespace",  df.bytes / (1024 * 1024) "Size (MB)",
       SUM(fs.bytes) / (1024 * 1024) "Free (MB)", Nvl(Round(SUM(fs.bytes) * 100 / df.bytes),1) "% Free", Round((df.bytes - SUM(fs.bytes)) * 100 / df.bytes) "% Used"
  FROM dba_free_space fs, (SELECT tablespace_name,SUM(bytes) bytes
          FROM dba_data_files
         GROUP BY tablespace_name) df
 WHERE fs.tablespace_name (+)  = df.tablespace_name
 GROUP BY df.tablespace_name,df.bytes
UNION ALL
SELECT /* + RULE */ df.tablespace_name tspace,
       fs.bytes / (1024 * 1024), SUM(df.bytes_free) / (1024 * 1024), Nvl(Round((SUM(fs.bytes) - df.bytes_used) * 100 / fs.bytes), 1), Round((SUM(fs.bytes) - df.bytes_free) * 100 / fs.bytes)
  FROM dba_temp_files fs, (SELECT tablespace_name,bytes_free,bytes_used
          FROM v$temp_space_header
         GROUP BY tablespace_name,bytes_free,bytes_used) df
 WHERE fs.tablespace_name (+)  = df.tablespace_name
 GROUP BY df.tablespace_name,fs.bytes,df.bytes_free,df.bytes_used
 ORDER BY 4 DESC;

Track Redo generation by day:
select trunc(completion_time) logdate, count(*) logswitch, round((sum(blocks*block_size)/1024/1024)) "REDO PER DAY (MB)" from v$archived_log
group by trunc(completion_time) order by 1;

Track Logon time of DB user and OS user:
Select to_char(logon_time,'dd/mm/yyyy hh24:mi:ss'),osuser,status,schemaname,machine from v$session where type !='BACKGROUND';