默认是parallel_max_servers是大于0的 也就是打开的
alter session enable parallel [ddl | dml | query];
alter session disable parallel [ddl | dml | query];
alter session force parallel ddl parallel 5;
用来分析DB性能的几个view.
V$PROCESS
Contains information about the currently active processes
V$SESSION
Lists session information for each current session
V$SESS_IO
Contains I/O statistics for each user session
V$SESSION_LONGOPS
Displays the status of various operations that run for longer than 6 seconds (in absolute time). These operations currently include many backup and recovery functions, statistics gathering, and query execution. More operations are added for every Oracle Database release.
V$SESSION_WAIT
Displays the current or last wait for each session
V$SESSION_WAIT_HISTORY
Lists the last ten wait events for each active session
V$WAIT_CHAINS
Displays information about blocked sessions
V$SYSSTAT
Contains session statistics
V$RESOURCE_LIMIT
Provides information about current and maximum global resource utilization for some system resources
V$SQLAREA
Contains statistics about shared SQL areas. Contains one row for each SQL string. Provides statistics about SQL statements that are in memory, parsed, and ready for execution
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