三种不同类型的latch

==================smon trace content==================

SMON: system monitor process posted

WAIT #0: nam='log file switch completion' ela= 0 p1=0 p2=0 p3=0 obj#=1 tim=1278243332801935

WAIT #0: nam='log file switch completion' ela= 0 p1=0 p2=0 p3=0 obj#=1 tim=1278243332815568

WAIT #0: nam='latch: row cache objects' ela= 95 address=2979418792 number=200 tries=1 obj#=1 tim=1278243333332734

WAIT #0: nam='latch: row cache objects' ela= 83 address=2979418792 number=200 tries=1 obj#=1 tim=1278243333356173

WAIT #0: nam='latch: undo global data' ela= 104 address=3066991984 number=187 tries=1 obj#=1 tim=1278243347987705

WAIT #0: nam='latch: object queue header operation' ela= 89 address=3094817048 number=131 tries=0 obj#=1 tim=1278243362468042

WAIT #0: nam='log file switch (checkpoint incomplete)' ela= 0 p1=0 p2=0 p3=0 obj#=1 tim=1278243419588202

Dead transaction 0x00c2.008.0000006d recovered by SMON

 

=====================

PARSING IN CURSOR #3 len=358 dep=1 uid=0 oct=3 lid=0 tim=1278243423594568 hv=3186851936 ad='ae82c1b8'

select smontabv.cnt,

       smontab.time_mp,

       smontab.scn,

       smontab.num_mappings,

       smontab.tim_scn_map,

       smontab.orig_thread

  from smon_scn_time smontab,

       (select max(scn) scnmax,

               count(*) + sum(NVL2(TIM_SCN_MAP, NUM_MAPPINGS, 0)) cnt

          from smon_scn_time

         where thread = 0) smontabv

 where smontab.scn = smontabv.scnmax

   and thread = 0

 

END OF STMT

PARSE #3:c=0,e=1354526,p=0,cr=0,cu=0,mis=1,r=0,dep=1,og=4,tim=1278243423594556

EXEC #3:c=0,e=106,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=1278243423603269

FETCH #3:c=0,e=47065,p=0,cr=319,cu=0,mis=0,r=1,dep=1,og=4,tim=1278243423650375

*** 2011-06-24 21:19:25.899

WAIT #0: nam='smon timer' ela= 299999999 sleep time=300 failed=0 p3=0 obj#=1 tim=1278243716699171

kglScanDependencyHandles4Unpin():

  cumscan=3 cumupin=4 time=776 upinned=0

 

以上SMON回滚清理Dead transaction的过程从”system monitor process posted”开始到”Dead transaction 0x00c2.008.0000006d recovered by SMON”结束。另外可以看到在恢复过程中SMON先后请求了’latch: row cache objects’、’latch: undo global data’、’latch: object queue header operation’三种不同类型的latch。本文转自cuug官网。