oracle 11g RAC 等待一例 gc current request 和 enq: US - contention

测试环境，11G R2 RAC。

有个脚本执行的时候，挂住了。检查一下：

SQL> select * from GV$SESSION_WAIT where sid = 2848 ;
 
   INST_ID        SID       SEQ# EVENT                                                            P1TEXT                                                                   P1 P1RAW            P2TEXT                                                                   P2 P2RAW            P3TEXT                                                                   P3 P3RAW            WAIT_CLASS_ID WAIT_CLASS# WAIT_CLASS                                                        WAIT_TIME SECONDS_IN_WAIT STATE               WAIT_TIME_MICRO TIME_REMAINING_MICRO TIME_SINCE_LAST_WAIT_MICRO
---------- ---------- ---------- ---------------------------------------------------------------- ---------------------------------------------------------------- ---------- ---------------- ---------------------------------------------------------------- ---------- ---------------- ---------------------------------------------------------------- ---------- ---------------- ------------- ----------- ---------------------------------------------------------------- ---------- --------------- ------------------- --------------- -------------------- --------------------------
         1       2848         85 gc current request                                               file#                                                                     4 0000000000000004 block#                                                                  128 0000000000000080 id#                                                                16777253 0000000001000025    3871361733          11 Cluster                                                                   0             767 WAITING                   766899151                   -1                          0
         2       2848         17 enq: US - contention                                             name|mode                                                        1431502854 0000000055530006 undo segment #                                                           17 0000000000000011 0                                                                         0 00                  1893977003           0 Other                                                                     0          139240 WAITING                139240348081                   -1                          0
 
SQL>

第一个事件：

SQL> select name,parameter1,parameter2,parameter3 from v$event_name where name='gc current request';
 
NAME                                                             PARAMETER1                                                       PARAMETER2                                                       PARAMETER3
---------------------------------------------------------------- ---------------------------------------------------------------- ---------------------------------------------------------------- ----------------------------------------------------------------
gc current request                                               file#                                                            block#                                                           id#
 
SQL> SELECT tablespace_name, file_name FROM dba_data_files WHERE file_id = 4;
 
TABLESPACE_NAME                FILE_NAME
------------------------------ --------------------------------------------------------------------------------
UNDOTBS2                       +XXX/xxx/undotbs02.dbf
 
SQL>

第二个也是说明UNDO的争用。

SQL> col file_name format a50   
SQL> set lines 100
SQL> select file_name,bytes/1024/1024 from dba_data_files order by file_name;

那就扩空间吧。