oracle library cache相關的等待事件及latch

Library cache中相關的latch包括：shared pool latch，
                                library cahce latch，
                                library cache lock latch，
                                library cache pin latch。

Share pool latch的主要作用是分配或釋放空間時使用，從Oracle9i開始，sharedpool被分成了很多個subpool，
由多個shared pool latch保護，Oracle開始支援更大的shared pool。

Library cache latch的主要作用是在hash bucket中定位handle時使用，

library cache lock latch和library cache pin latch分別是獲取lock和pin時，需要取得的latch。

shared pool大小不合理，大量的硬解析以及SQL版本過多都可能導致shared pool latch和library cache latch的爭用。

從Oracle10g開始，Oracle正在逐步用mutex取代library cache中的latch，
cursor：pin S和cursor：pin X相當於share和exclusive型別的library cache pin，
cursor：pin S wait on X則表示share方式正在等待exclusive鎖定。

/********與library cache相關的等待事件**********/
SQL> select * from v$event_name where name like '%library cache%';
 
    EVENT#   EVENT_ID NAME                           PARAMETER1                     PARAMETER2           PARAMETER3           WAIT_CLASS_ID  WAIT_CLASS
---------- ---------- ------------------------------ ------------------------------ -------------------- -------------------- -------------  --------------------
       280 2802704141 library cache pin              handle address                 pin address          100*mode+namespace      3875070507  Concurrency
       281  916468430 library cache lock             handle address                 lock address         100*mode+namespace      3875070507  Concurrency
       282 2952162927 library cache load lock        object address                 lock address         100*mask+namespace      3875070507  Concurrency
       283 1646780882 library cache: mutex X         idn                            value                where                   3875070507  Concurrency
       284 2446268751 library cache: mutex S         idn                            value                where                   3875070507  Concurrency
       815  800384622 library cache revalidation                                                                                 1893977003  Other
       816 1578286316 library cache shutdown                                                                                     1893977003  Other
 
7 rows selected

可知基本與併發訪問有關