How to find and investigate a process in top command output?

Total connection by machine:
SQL> select machine, count(*) from v$session group by machine order by 2;

Total number of database user who connected:
SQL> select count(1) "NO. Of DB Users Connected", to_char(sysdate,'DD-MON-YYYY:HH24:MI:SS') sys_time from v$session where username is NOT NULL;

Define a process(pid) from top:
17831 ora11g .. ora_m000_ALPERDB  

Get detailed info from database:
SQL> select * from v$process where spid = 17831;
-> M000 means MMON Slave Process
-> e.g. pid -> 16, sid -> 555

SQL>
SELECT s.username, osuser, process machine, p.terminal, type, sid, s.serial#, s.program
FROM v$session s, v$process p
WHERE p.pid = 16
AND s.paddr = p.addr;

SQL> select * from gv$session where sid = 555;

Get sql from below code related to example process if it has SQL:
SQL>
SELECT 
      s.sid
     ,s.CLIENT_INFO
     ,s.MACHINE
     ,s.PROGRAM
     ,s.TYPE
     ,s.logon_time
     ,s.osuser
     ,sq.sorts
     ,sq.DISK_READS
     ,sq.BUFFER_GETS
     ,sq.ROWS_PROCESSED
     ,sq.SQLTYPE
     ,sq.SQL_TEXT
 FROM gv$session s    
    , gv$sql sq
WHERE s.SQL_HASH_VALUE = sq.HASH_VALUE
  --AND s.inst_id= 1
  AND s.sid = 555 
  AND sq.inst_id= s.inst_id

output columns of top command

Columns:
PID     -> Process ID   
USER    -> Process owner   
PR      -> Priority of process 
NI      -> Nice value of process  
VIRT    -> Virtual memory using by process
RES     -> Physical memory using by process  
SHR     -> Shared memory of process
S       -> Status of process (R-> Running, S-> Sleeep, Z-> Zombie, D-> Uninterruptible Sleep, T-> Traced or Stopped)
%CPU    -> CPU usage of process (as percent)
%MEM    -> RAM usage of process (as percent)
TIME+   -> Total time activity for process 
COMMAND -> indicates of process name

Info:
PR = 20 + NI (PR-RT -> Real Time system process)
PR -> (0 is the highest priority and 39 is the lowest priority)
NI; Nice value (−20 is the highest priority and 19 is the lowest priority)
VIRT; Virtual image (kb) -> disk storage + RAM
RES;  Resident size (kb) -> RAM (non-swapped physical memory)

SHR; Shared mem size (kb)-> RAM (shared memory)

Extras:

Set priority of a process before start;
nice -n 19 tar cvzf archive.tgz largefile

Change priority of a process;
renice -n -20 -p process_id

Ref:

https://ozsoyler.blogspot.com/2017/01/how-to-see-load-averages-on-linux.html

https://ozsoyler.blogspot.com/2014/10/how-to-see-process-that-used-memory-or.html

How to see load averages on linux?

$ top
or 
$ uptime

e.g.
load average: 0.35. 0.23, 0.25
First column; last one minute
Second column; last five minutes
Third column;  last fifteen minutes averages for each cpu

How to see process that used memory or CPU at most?

Please run the command as linux system user.

# top
at manual -> shift + f and then n (mem) or k (cpu)

to highlight the column: press b

to sort by time: press shift + t

to see all CPUs: press 1

to get the different graphical output: press t

Note: Type and press enter bold ones to run

How to select top 10 records in Oracle 11g and 12c?

In 11g:

As you now that TOP keyword does not exist in 11g, but you can use rownum keyword to query top records.

For example, you want to see top 10 salary records based on employees:

Run that SQL in your editor's SQL window.

Wrong one;
SELECT *
FROM (
 SELECT employee_id, first_name, last_name, salary
 FROM employees
 )
WHERE rownum < 11
ORDER BY salary DESC;

* ORDER BY runs at last so that it should be in sub query.

Correct one;
SELECT *
FROM (
 SELECT employee_id, first_name, last_name, salary
 FROM employees
 ORDER BY salary DESC
 )
WHERE rownum < 11;

In 12c:
With 12c, you may use special syntax to see top records that is "FETCH" syntax.

SELECT employee_id, first_name, last_name, salary
FROM employees
ORDER BY salary DESC
FETCH FIRST 10 ROWS ONLY;

Also, you may disregard first 5 records inside 10 records.

SELECT employee_id, first_name, last_name, salary
FROM employees
ORDER BY salary DESC
OFFSET 5 ROWS 
FETCH NEXT 5 ROWS ONLY;

That's all. Bye :)