怎么理解pid 、spid 、sid 和session_id？

[winson1740]

SELECT P.pid,S.sid,s.serial#,P.spid,S.username,S.osuser,
P.serial#,P.terminal,P.program,P.background,S.status,A.sql_text
FROM v$process P, v$session S,v$sqlarea A WHERE
P.addr = s.paddr AND S.sql_address = a.address (+)
order by P.spid;

select username,sid,serial# from v$session where sid=session_id;

select d.value || '/' || lower(rtrim(i.instance, chr(0))) || '_ora_' ||
p.spid || '.trc' trace_file_name
from (select p.spid
from sys.v$session s, sys.v$process p
where s.sid = :sid
and p.addr = s.paddr) p,
(select t.instance
from sys.v$thread t, sys.v$parameter v
where v.name = 'thread'
and (v.value = 0 or t.thread# = to_number(v.value))) i,
(select value from sys.v$parameter where name = 'user_dump_dest') d;



请问一下以上三个语句中涉及到的pid、spid、sid、session_id是啥意思？这里的pid是和在Unix操作系统中的pid一样的吗？

[chenqingyu]

pid肯定是进程号啦..
spid是子进程?
你这里的sid和session_id都是会话ID.

不过一般说sid都是指的servic_id,也说是服务名啦.