session:
Because every login requires a session, this parameter effectively determines the maximum number of concurrent users in the system. You should always set this parameter explicitly to a value equivalent to your estimate of the maximum number of concurrent users, plus the number of background processes, plus approximately 10% for recursive sessions.
12c (1.5 * PROCESSES) + 22
ALTER SYstem can be used in a PDB only to change the value of the SESSIONS parameter for that PDB. (仅限在PDB中修改)
For a CDB, the root container's SESSIONS parameter specifies the total number of sessions for the database.
the SESSIONS parameter does not count recursive sessions and hence does not require the 10% adjustment.
process --- 针对的操作系统进程(这里不做详述,专属和共享模式),而session是db层,两个概念不同。
这里涉及到的试图有:(其中概念可以查看官档)
gv$session
gv$process
v$resource_limit
v$license
---这里有个捷径提醒下,修改这个参数一般人会重启cdb,但是其实可以在某个节点修改sessions,然后shutdown immediate(当然要快速生效也可以shutdown abort)其中一个cdb节点,然后startup,同样可以生效,但是记得要在把这个节点运行的service要start。
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