1 2 3 Previous Next 31 Replies Latest reply: Mar 17, 2013 12:43 PM by Jonathan Lewis Go to original post RSS
      • 15. Re: Log Buffer
        996125
        SGA Info from v$sgainfo where you can see granule size
        Name     Bytes     RESIZEABLE
        Fixed SGA Size     2172576     No
        Redo Buffers     82812928     No
        Buffer Cache Size     17179869184     Yes
        Shared Pool Size     6710886400     Yes
        Large Pool Size     67108864     Yes
        Java Pool Size     469762048     Yes
        Streams Pool Size     67108864     Yes
        Shared IO Pool Size     0     Yes
        Granule Size     67108864     No
        Maximum SGA Size     27800952832     No
        Startup overhead in Shared Pool     952671912     No
        Free SGA Memory Available     3221225472     
        • 16. Re: Log Buffer
          Jonathan Lewis
          <blockquote>
          Further information that would help - the top section of a 1 hour AWR report around a time when the log file sync waits appear to be a problem. in this case I would want to see the section of the report that includes the background waits as well as the usual "heading, load profile, top N" sections, and the "Instance Activity".

          It looks like you're trying to cut and paste from an html output.
          Use SQL*Plus to run $ORACLE_HOME/rdbms/admin/awrrpt to get a text format which will behave nicely with the code tags.</blockquote>

          If you're not going to supply requested information I'm unlikely to be motivated to help.

          As it is, I might take a wild stab in the dark and guess that you're running on a Sun box with 8 cores.

          Regards
          Jonathan Lewis
          • 17. Re: Log Buffer
            Jan-Marten Spit
            okay, so your IO subsystem does not seem to be the culprit here.

            please provide the info jonathan lewis asks for, and give info on the used platform. i want to know what the problem is too :)
            • 18. Re: Log Buffer
              996125
              PS attached below complete wait profile, load profile etc
              WORKLOAD REPOSITORY report for
              
              DB Name         DB Id    Instance     Inst Num Startup Time    Release     RAC
              ------------ ----------- ------------ -------- --------------- ----------- ---
              PRD           4177979038 PRD                 1 24-Feb-13 16:36 11.2.0.3.0  NO
              
              Host Name        Platform                         CPUs Cores Sockets Memory(GB)
              ---------------- -------------------------------- ---- ----- ------- ----------
              chbsux0200       Solaris[tm] OE (64-bit)            64    32       8      64.00
              
                            Snap Id      Snap Time      Sessions Curs/Sess
                          --------- ------------------- -------- ---------
              Begin Snap:     38744 07-Mar-13 10:45:11       365      25.0
                End Snap:     38748 07-Mar-13 11:45:42       367      28.7
                 Elapsed:               60.52 (mins)
                 DB Time:            1,950.42 (mins)
              
              Cache Sizes                       Begin        End
              ~~~~~~~~~~~                  ---------- ----------
                             Buffer Cache:    11,008M    11,008M  Std Block Size:         8K
                         Shared Pool Size:     6,528M     6,528M      Log Buffer:   211,944K
              
              Load Profile              Per Second    Per Transaction   Per Exec   Per Call
              ~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
                    DB Time(s):               32.2                3.8       0.03       0.28
                     DB CPU(s):                8.9                1.1       0.01       0.08
                     Redo size:        1,623,930.8          190,449.9
                 Logical reads:          344,928.5           40,452.2
                 Block changes:            2,707.5              317.5
                Physical reads:            3,875.4              454.5
               Physical writes:              395.0               46.3
                    User calls:              116.4               13.7
                        Parses:               43.5                5.1
                   Hard parses:                2.5                0.3
              W/A MB processed:               90.3               10.6
                        Logons:                0.4                0.0
                      Executes:            1,263.2              148.1
                     Rollbacks:                1.0                0.1
                  Transactions:                8.5
              
              Instance Efficiency Percentages (Target 100%)
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                          Buffer Nowait %:  100.00       Redo NoWait %:   99.91
                          Buffer  Hit   %:   99.75    In-memory Sort %:  100.00
                          Library Hit   %:   99.60        Soft Parse %:   94.36
                       Execute to Parse %:   96.56         Latch Hit %:   98.86
              Parse CPU to Parse Elapsd %:   20.49     % Non-Parse CPU:   99.86
              
               Shared Pool Statistics        Begin    End
                                            ------  ------
                           Memory Usage %:   62.12   61.86
                  % SQL with executions>1:   95.33   96.06
                % Memory for SQL w/exec>1:   91.06   88.26
              
              Top 5 Timed Foreground Events
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                                         Avg
                                                                        wait   % DB
              Event                                 Waits     Time(s)   (ms)   time Wait Class
              ------------------------------ ------------ ----------- ------ ------ ----------
              log file sync                        10,940      54,627   4993   46.7 Commit
              DB CPU                                           32,451          27.7
              log buffer space                        449       8,173  18203    7.0 Configurat
              enq: UL - contention                      7       7,285 1.E+06    6.2 Applicatio
              SQL*Net message from dblink         108,681       4,617     42    3.9 Network
              Host CPU (CPUs:   64 Cores:   32 Sockets:    8)
              ~~~~~~~~         Load Average
                             Begin       End     %User   %System      %WIO     %Idle
                         --------- --------- --------- --------- --------- ---------
                             25.05      8.20      14.0       0.9       0.0      85.1
              
              Instance CPU
              ~~~~~~~~~~~~
                            % of total CPU for Instance:      14.3
                            % of busy  CPU for Instance:      96.0
                %DB time waiting for CPU - Resource Mgr:       0.0
              
              Memory Statistics
              ~~~~~~~~~~~~~~~~~                       Begin          End
                                Host Mem (MB):     65,536.0     65,536.0
                                 SGA use (MB):     23,552.0     23,552.0
                                 PGA use (MB):      3,785.1      3,172.6
                  % Host Mem used for SGA+PGA:        41.71        40.78
              
              Time Model Statistics              DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> Total time in database user-calls (DB Time): 117025.2s
              -> Statistics including the word "background" measure background process
                 time, and so do not contribute to the DB time statistic
              -> Ordered by % or DB time desc, Statistic name
              
              Statistic Name                                       Time (s) % of DB Time
              ------------------------------------------ ------------------ ------------
              sql execute elapsed time                             66,453.1         56.8
              DB CPU                                               32,450.6         27.7
              PL/SQL execution elapsed time                        29,674.9         25.4
              connection management call elapsed time               1,953.7          1.7
              parse time elapsed                                      245.0           .2
              hard parse elapsed time                                 108.5           .1
              Java execution elapsed time                              46.5           .0
              inbound PL/SQL rpc elapsed time                          40.6           .0
              RMAN cpu time (backup/restore)                           34.2           .0
              sequence load elapsed time                               18.6           .0
              hard parse (sharing criteria) elapsed time               15.6           .0
              PL/SQL compilation elapsed time                          12.6           .0
              repeated bind elapsed time                                2.2           .0
              hard parse (bind mismatch) elapsed time                   1.9           .0
              failed parse elapsed time                                 0.2           .0
              DB time                                             117,025.2
              background elapsed time                               6,890.2
              background cpu time                                     754.5
                        -------------------------------------------------------------
              
              Operating System Statistics         DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> *TIME statistic values are diffed.
                 All others display actual values.  End Value is displayed if different
              -> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name
              
              Statistic                                  Value        End Value
              ------------------------- ---------------------- ----------------
              AVG_BUSY_TIME                             53,872
              AVG_IDLE_TIME                            308,864
              AVG_SYS_TIME                               3,019
              AVG_USER_TIME                             50,683
              BUSY_TIME                              3,459,745
              IDLE_TIME                             19,779,080
              SYS_TIME                                 204,469
              USER_TIME                              3,255,276
              LOAD                                          25                8
              OS_CPU_WAIT_TIME                          19,500
              RSRC_MGR_CPU_WAIT_TIME                         0
              VM_IN_BYTES                           34,332,672
              VM_OUT_BYTES                                   0
              PHYSICAL_MEMORY_BYTES             68,719,476,736
              NUM_CPUS                                      64
              NUM_CPU_CORES                                 32
              NUM_CPU_SOCKETS                                8
              TCP_RECEIVE_SIZE_DEFAULT                  49,152
              TCP_RECEIVE_SIZE_MAX                   1,048,576
              TCP_SEND_SIZE_DEFAULT                     49,152
              TCP_SEND_SIZE_MAX                      1,048,576
                        -------------------------------------------------------------
              
              Operating System Statistics - DetailDB/Inst: PRD/PRD  Snaps: 38744-38748
              
              Snap Time           Load    %busy    %user     %sys    %idle  %iowait
              --------------- -------- -------- -------- -------- -------- --------
              07-Mar 10:45:11     25.1      N/A      N/A      N/A      N/A      N/A
              07-Mar 11:00:20      7.1     13.3     12.2      1.1     86.7      0.0
              07-Mar 11:15:27     11.0     12.1     11.4      0.7     87.9      0.0
              07-Mar 11:30:40     10.0     18.3     17.3      0.9     81.7      0.0
              07-Mar 11:45:42      8.2     15.8     15.1      0.7     84.2      0.0
                        -------------------------------------------------------------
              
              Foreground Wait Class               DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> s  - second, ms - millisecond -    1000th of a second
              -> ordered by wait time desc, waits desc
              -> %Timeouts: value of 0 indicates value was < .5%.  Value of null is truly 0
              -> Captured Time accounts for        100.3%  of Total DB time     117,025.16 (s)
              -> Total FG Wait Time:            84,908.83 (s)  DB CPU time:      32,450.55 (s)
              
                                                                                Avg
                                                    %Time       Total Wait     wait
              Wait Class                      Waits -outs         Time (s)     (ms)  %DB time
              -------------------- ---------------- ----- ---------------- -------- ---------
              Commit                         10,940     0           54,627     4993      46.7
              DB CPU                                                32,451               27.7
              Configuration                     509     0            8,438    16577       7.2
              Application                     2,934     0            7,455     2541       6.4
              User I/O                    1,646,567     0            4,781        3       4.1
              Concurrency                    12,622     0            4,756      377       4.1
              Network                     3,325,926     0            4,691        1       4.0
              Other                           2,621     2               58       22       0.0
              Administrative                      2     0               56    27997       0.0
              System I/O                     48,064     0               47        1       0.0
                        -------------------------------------------------------------
              
              Foreground Wait Events             DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> s  - second, ms - millisecond -    1000th of a second
              -> Only events with Total Wait Time (s) >= .001 are shown
              -> ordered by wait time desc, waits desc (idle events last)
              -> %Timeouts: value of 0 indicates value was < .5%.  Value of null is truly 0
              
                                                                           Avg
                                                      %Time Total Wait    wait    Waits   % DB
              Event                             Waits -outs   Time (s)    (ms)     /txn   time
              -------------------------- ------------ ----- ---------- ------- -------- ------
              log file sync                    10,940     0     54,627    4993      0.4   46.7
              log buffer space                    449     0      8,173   18203      0.0    7.0
              enq: UL - contention                  7     0      7,285 1.0E+06      0.0    6.2
              SQL*Net message from dblin      108,681     0      4,617      42      3.5    3.9
              buffer busy waits                 2,159     0      4,322    2002      0.1    3.7
              direct path write temp          532,990     0      1,339       3     17.2    1.1
              db file sequential read         618,070     0      1,009       2     20.0     .9
              db file scattered read          157,508     0      1,007       6      5.1     .9
              direct path read                287,780     0        774       3      9.3     .7
              local write wait                    155     0        590    3808      0.0     .5
              latch: In memory undo latc          185     0        420    2273      0.0     .4
              log file switch completion           29     0        257    8865      0.0     .2
              enq: RO - fast object reus           88     0        159    1804      0.0     .1
              switch logfile command                2     0         56   27997      0.0     .0
              SQL*Net more data to clien    2,329,074     0         49       0     75.2     .0
              PX Deq: Table Q Get Keys             32     0         48    1486      0.0     .0
              control file single write           136     0         31     227      0.0     .0
              direct path sync                    885     0         25      28      0.0     .0
              SQL*Net more data from dbl      384,888     0         24       0     12.4     .0
              direct path read temp               734     0         23      31      0.0     .0
              read by other session             1,254     0         10       8      0.0     .0
              Log archive I/O                   1,905     0          9       5      0.1     .0
              write complete waits                 19     0          7     392      0.0     .0
              cursor: pin S wait on X             143     0          7      48      0.0     .0
              recovery area: computing o            5     0          7    1337      0.0     .0
              enq: TM - contention                 10     0          6     629      0.0     .0
              control file sequential re       45,705     0          4       0      1.5     .0
              SQL*Net break/reset to cli        2,804     0          3       1      0.1     .0
              os thread startup                    32     0          3      86      0.0     .0
              library cache: mutex X            2,552     0          3       1      0.1     .0
              direct path write                11,170     0          3       0      0.4     .0
              imm op                                4     0          2     578      0.0     .0
              log file sequential read            245     0          2       9      0.0     .0
              enq: TX - row lock content           20     0          2      90      0.0     .0
              Disk file operations I/O         35,912     0          2       0      1.2     .0
              latch: cache buffers chain        5,898     0          1       0      0.2     .0
              recovery area: computing b            1     0          1     588      0.0     .0
              control file parallel writ           73     0          1       8      0.0     .0
              SQL*Net message to client       392,081     0          0       0     12.7     .0
              PX Deq: Slave Session Stat          732     0          0       1      0.0     .0
              PX Deq: Signal ACK EXT              368     0          0       1      0.0     .0
              library cache lock                    6     0          0      37      0.0     .0
              enq: KO - fast object chec            5     0          0      42      0.0     .0
              recovery area: computing d            1     0          0     199      0.0     .0
              log file switch (private s            2     0          0      94      0.0     .0
              db file parallel read                 7     0          0      24      0.0     .0
              SQL*Net more data to dblin        1,974     0          0       0      0.1     .0
              enq: TX - index contention            9     0          0      13      0.0     .0
              kksfbc child completion               2   100          0      50      0.0     .0
              SQL*Net message to dblink       108,593     0          0       0      3.5     .0
              latch: object queue header          502     0          0       0      0.0     .0
              ksdxexeotherwait                      3     0          0      20      0.0     .0
              enq: HW - contention                  8     0          0       7      0.0     .0
              cursor: pin S                     1,451     0          0       0      0.0     .0
              latch free                          203     0          0       0      0.0     .0
              enq: PS - contention                 64     0          0       0      0.0     .0
              reliable message                    114     0          0       0      0.0     .0
              SQL*Net more data from cli          635     0          0       0      0.0     .0
              enq: CF - contention                  4     0          0       6      0.0     .0
              PX Deq: Signal ACK RSG              368     0          0       0      0.0     .0
              Foreground Wait Events             DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> s  - second, ms - millisecond -    1000th of a second
              -> Only events with Total Wait Time (s) >= .001 are shown
              -> ordered by wait time desc, waits desc (idle events last)
              -> %Timeouts: value of 0 indicates value was < .5%.  Value of null is truly 0
              
                                                                           Avg
                                                      %Time Total Wait    wait    Waits   % DB
              Event                             Waits -outs   Time (s)    (ms)     /txn   time
              -------------------------- ------------ ----- ---------- ------- -------- ------
              latch: redo allocation               27     0          0       1      0.0     .0
              latch: shared pool                  123     0          0       0      0.0     .0
              Parameter File I/O                    2     0          0       5      0.0     .0
              utl_file I/O                        100     0          0       0      0.0     .0
              undo segment extension                2   100          0       5      0.0     .0
              latch: parallel query allo           16     0          0       0      0.0     .0
              latch: cache buffers lru c           21     0          0       0      0.0     .0
              latch: row cache objects             52     0          0       0      0.0     .0
              rdbms ipc reply                      50     0          0       0      0.0     .0
              latch: call allocation               10     0          0       0      0.0     .0
              SQL*Net message from clien      392,066     0    638,356    1628     12.7
              Streams AQ: waiting for me        8,642    93     70,764    8188      0.3
              PL/SQL lock timer                   244   101     28,203  115584      0.0
              jobq slave wait                   7,294    99      3,631     498      0.2
              PX Deq: Table Q Normal              538     0        142     265      0.0
              PX Deq: Execution Msg             6,757     0         86      13      0.2
              PX Deq: Table Q Sample               48     0         72    1504      0.0
              PX Deq: Execute Reply             5,972     0         25       4      0.2
              PX Deq Credit: send blkd            194     0         12      64      0.0
              single-task message                  86     0          6      65      0.0
              PX Deq: Parse Reply                 352     0          1       3      0.0
              PX Deq: Join ACK                    352     0          0       0      0.0
              PX Deq: Msg Fragment                 48     0          0       0      0.0
                        -------------------------------------------------------------
              
              Background Wait Events             DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> ordered by wait time desc, waits desc (idle events last)
              -> Only events with Total Wait Time (s) >= .001 are shown
              -> %Timeouts: value of 0 indicates value was < .5%.  Value of null is truly 0
              
                                                                           Avg
                                                      %Time Total Wait    wait    Waits   % bg
              Event                             Waits -outs   Time (s)    (ms)     /txn   time
              -------------------------- ------------ ----- ---------- ------- -------- ------
              log file parallel write         123,919     0      3,070      25      4.0   44.6
              db file parallel write           57,820     0      1,484      26      1.9   21.5
              log file sync                        26     0        491   18899      0.0    7.1
              log buffer space                     29     0        447   15409      0.0    6.5
              buffer busy waits                    42     0        326    7774      0.0    4.7
              Backup: MML write backup p       25,770     0        131       5      0.8    1.9
              io done                          13,039     1        126      10      0.4    1.8
              Log archive I/O                   7,374     0         46       6      0.2     .7
              control file single write           155     0         37     237      0.0     .5
              enq: JD - contention                  2     0         32   15907      0.0     .5
              log file switch completion            3     0         29    9693      0.0     .4
              control file parallel writ        2,454     0         18       7      0.1     .3
              db file sequential read           3,990     0         15       4      0.1     .2
              os thread startup                   156     0         14      87      0.0     .2
              imm op                               19    16         13     708      0.0     .2
              row cache lock                        1   100          6    6000      0.0     .1
              db file async I/O submit          4,796     0          3       1      0.2     .0
              Disk file operations I/O          5,131     0          2       0      0.2     .0
              direct path write                   130     0          1      12      0.0     .0
              control file sequential re       29,174     0          1       0      0.9     .0
              direct path sync                     24     0          1      52      0.0     .0
              slave exit                            4    50          1     250      0.0     .0
              RMAN backup & recovery I/O           67     0          1      11      0.0     .0
              db file scattered read               39     0          1      18      0.0     .0
              log file sequential read            187     0          0       2      0.0     .0
              Backup: MML initialization            2     0          0     121      0.0     .0
              db file single write                  8     0          0      27      0.0     .0
              enq: CF - contention                  2     0          0      91      0.0     .0
              RMAN Tape slave I/O              25,790     0          0       0      0.8     .0
              log file single write                20     0          0       8      0.0     .0
              Backup: MML create a backu            3     0          0      35      0.0     .0
              enq: JS - queue lock                  5     0          0      20      0.0     .0
              latch: active service list          218     0          0       0      0.0     .0
              reliable message                     65     0          0       1      0.0     .0
              direct path read                      9     0          0       8      0.0     .0
              Backup: MML commit backup             3     0          0      24      0.0     .0
              undo segment extension                4   100          0      18      0.0     .0
              ADR block file read                  19     0          0       4      0.0     .0
              latch free                          468     0          0       0      0.0     .0
              Backup: MML query backup p            3     0          0      22      0.0     .0
              direct path write temp               12     0          0       4      0.0     .0
              latch: call allocation              159     0          0       0      0.0     .0
              LGWR wait for redo copy           1,217     0          0       0      0.0     .0
              ADR block file write                  8     0          0       4      0.0     .0
              library cache: mutex X              560     0          0       0      0.0     .0
              Backup: MML shutdown                  2     0          0       5      0.0     .0
              SQL*Net more data to clien          227     0          0       0      0.0     .0
              ADR file lock                        12     0          0       1      0.0     .0
              latch: messages                     115     0          0       0      0.0     .0
              latch: shared pool                   87     0          0       0      0.0     .0
              asynch descriptor resize            885   100          0       0      0.0     .0
              SQL*Net message to client         2,222     0          0       0      0.1     .0
              SQL*Net more data from cli          227     0          0       0      0.0     .0
              latch: cache buffers chain           81     0          0       0      0.0     .0
              latch: In memory undo latc            3     0          0       1      0.0     .0
              latch: redo writing                  25     0          0       0      0.0     .0
              rdbms ipc message               133,616    18     77,974     584      4.3
              Space Manager: slave idle         6,639    80     29,212    4400      0.2
              PX Idle Wait                        397     0     25,404   63991      0.0
              Streams AQ: qmn slave idle        1,048     0      7,256    6924      0.0
              Background Wait Events             DB/Inst: PRD/PRD  Snaps: 38744-38748
              -> ordered by wait time desc, waits desc (idle events last)
              -> Only events with Total Wait Time (s) >= .001 are shown
              -> %Timeouts: value of 0 indicates value was < .5%.  Value of null is truly 0
              
                                                                           Avg
                                                      %Time Total Wait    wait    Waits   % bg
              Event                             Waits -outs   Time (s)    (ms)     /txn   time
              -------------------------- ------------ ----- ---------- ------- -------- ------
              DIAG idle wait                    7,163   100      7,163    1000      0.2
              Streams AQ: qmn coordinato        1,405    37      3,628    2582      0.0
              pmon timer                        1,335    85      3,618    2710      0.0
              smon timer                           89     0      3,578   40207      0.0
              Streams AQ: waiting for ti          102    83      3,474   34062      0.0
              JOX Jit Process Sleep               231   100      3,465   15000      0.0
              i/o slave wait                   26,006     1        235       9      0.8
              SQL*Net message from clien        2,919     0        193      66      0.1
              class slave wait                     50     0          0       0      0.0
                        -------------------------------------------------------------
              • 19. Re: Log Buffer
                996125
                Please let me know if you need anything else apart from posted in previous message? PS below wait histogram below if you need.
                Wait Event Histogram               DB/Inst: PRD/PRD  Snaps: 38744-38748
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> % of Waits: value of .0 indicates value was <.05%; value of null is truly 0
                -> % of Waits: column heading of <=1s is truly <1024ms, >1s is truly >=1024ms
                -> Ordered by Event (idle events last)
                
                                                                    % of Waits
                                                 -----------------------------------------------
                                           Total
                Event                      Waits  <1ms  <2ms  <4ms  <8ms <16ms <32ms  <=1s   >1s
                -------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
                ADR block file read           19  63.2         5.3  10.5  15.8   5.3
                ADR block file write           8              37.5  62.5
                ADR file lock                 12  91.7               8.3
                ARCH wait for archivelog l    12 100.0
                Backup: MML commit backup      3                          33.3  33.3  33.3
                Backup: MML create a backu     3                                33.3  66.7
                Backup: MML extended initi     2 100.0
                Backup: MML initialization     2                                     100.0
                Backup: MML query backup p     3                               100.0
                Backup: MML shutdown           2                   100.0
                Backup: MML write backup p 25.8K          .0  19.6  79.6    .5    .2    .1
                Disk file operations I/O     41K 100.0          .0    .0    .0    .0    .0
                LGWR wait for redo copy     1215  99.9    .1
                Log archive I/O             9279  42.8  42.0  12.0    .1    .1    .1   2.8
                PX Deq: Signal ACK EXT       368  93.8   2.7    .3    .5   1.4    .8    .5
                PX Deq: Signal ACK RSG       368  98.6    .5    .8
                PX Deq: Slave Session Stat   736  85.3   5.8   5.8   2.6    .4
                PX Deq: Table Q Get Keys      32  56.3                           9.4  12.5  21.9
                PX Deq: Table Q qref          48 100.0
                PX qref latch                 37 100.0
                Parameter File I/O             4  75.0                    25.0
                RMAN Tape slave I/O        25.8K 100.0                            .0    .0
                RMAN backup & recovery I/O    67  41.8   4.5   9.0  16.4   7.5   4.5  16.4
                SQL*Net break/reset to cli  2797  95.0   4.0    .2    .3    .1          .4
                SQL*Net message from dblin 108.7        83.9  13.7   2.1    .1    .0    .2    .0
                SQL*Net message to client   394K 100.0
                SQL*Net message to dblink  108.6 100.0
                SQL*Net more data from cli   861 100.0
                SQL*Net more data from dbl 384.9  99.3    .4    .3    .0    .0    .0    .0
                SQL*Net more data to clien 2325. 100.0
                SQL*Net more data to dblin  1974  97.4   2.1    .5
                asynch descriptor resize     886 100.0
                buffer busy waits           2202  81.7   4.1   1.4    .2          .0   1.4  11.2
                buffer deadlock                1 100.0
                control file parallel writ  2528   4.7   4.9  20.1  56.7   9.8   1.7   2.1
                control file sequential re 74.9K  98.5    .9    .1    .3    .0    .0    .0
                control file single write    291   4.8   2.1   9.3  13.1    .3        70.4
                cursor: mutex S                2 100.0
                cursor: mutex X               10 100.0
                cursor: pin S               1449  99.9                      .1
                cursor: pin S wait on X      141                           1.4  62.4  36.2
                db file async I/O submit    4796  85.3   3.1   5.3   6.2    .1
                db file parallel read         59   3.4   3.4   1.7  27.1  45.8  15.3   3.4
                db file parallel write     57.9K  16.2  10.7  14.6  18.1  15.1  11.4  13.9    .2
                db file scattered read     157.4  42.5  19.5   2.7   4.6  16.7  12.6   1.4
                db file sequential read    619.8  89.6    .8   1.1   3.3   3.8    .7    .7    .0
                db file single write           8              12.5  12.5  50.0        25.0
                direct path read           287.6  62.1  12.9   6.4   8.9   7.1   2.1    .6
                direct path read temp        734  67.0    .5   2.5    .3   1.0   7.1  21.7
                direct path sync             909  12.9   3.2   3.1  19.1  29.3   7.8  24.6
                direct path write          11.3K  98.7    .1    .2    .3    .4    .2    .2
                direct path write temp      532K  97.5    .0    .0    .0    .1    .3   2.0    .0
                enq: CF - contention           6  33.3  16.7        16.7        16.7  16.7
                enq: HW - contention           8  50.0        12.5  25.0              12.5
                enq: JD - contention           2                                           100.0
                enq: JS - queue lock           5                          60.0  20.0  20.0
                enq: KO - fast object chec     5                    20.0  40.0  20.0  20.0
                enq: PS - contention          64  96.9                     3.1
                enq: RO - fast object reus    88  38.6               3.4   3.4   8.0  34.1  12.5
                enq: TM - contention          10                                      90.0  10.0
                Wait Event Histogram               DB/Inst: PRD/PRD  Snaps: 38744-38748
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> % of Waits: value of .0 indicates value was <.05%; value of null is truly 0
                -> % of Waits: column heading of <=1s is truly <1024ms, >1s is truly >=1024ms
                -> Ordered by Event (idle events last)
                
                                                                    % of Waits
                                                 -----------------------------------------------
                                           Total
                Event                      Waits  <1ms  <2ms  <4ms  <8ms <16ms <32ms  <=1s   >1s
                -------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
                enq: TX - index contention     9  22.2        11.1  11.1  44.4        11.1
                enq: TX - row lock content    20  65.0                    15.0  10.0   5.0   5.0
                enq: UL - contention           7  14.3        14.3  14.3              14.3  42.9
                imm op                        23                                 4.3  95.7
                io done                      13K    .1    .0    .1  18.0  80.3   1.4
                kksfbc child completion        2                                     100.0
                ksdxexeotherwait               3                          66.7        33.3
                latch free                   671  99.9                            .1
                latch: In memory undo latc   188  85.6    .5                                13.8
                latch: active service list   220  88.2   4.1   7.7
                latch: cache buffers chain  5978  99.7    .3    .1
                latch: cache buffers lru c    28  96.4   3.6
                latch: call allocation       169 100.0
                latch: checkpoint queue la    12 100.0
                latch: enqueue hash chains     1 100.0
                latch: messages              115 100.0
                latch: object queue header   532  97.9   2.1
                latch: parallel query allo    16 100.0
                latch: redo allocation        30  73.3  26.7
                latch: redo writing           25 100.0
                latch: row cache objects      52 100.0
                latch: shared pool           210 100.0
                latch: undo global data        2 100.0
                library cache lock             6                                50.0  50.0
                library cache: mutex X      3074  92.1                     7.2    .7
                local write wait             155         5.2   9.7   9.7  29.7  22.6  12.3  11.0
                log buffer space             478                                  .2   5.4  94.4
                log file parallel write    123.5  10.2   8.4  29.0  39.6  10.6   1.3    .6    .2
                log file sequential read     432  47.0  13.0   6.3  11.3   9.7   8.3   4.4
                log file single write         20  10.0   5.0  25.0  20.0  20.0  20.0
                log file switch (private s     2                                     100.0
                log file switch completion    32                                           100.0
                log file sync                11K                          47.4  18.1  10.5  24.0
                os thread startup            188                                     100.0
                rdbms ipc reply               50 100.0
                read by other session       1254  25.4  11.3   4.5  19.0  27.8  11.3    .7
                recovery area: computing b     1                                     100.0
                recovery area: computing d     1                                     100.0
                recovery area: computing o     5  40.0              20.0                    40.0
                reliable message             179  70.9  23.5   3.9   1.1    .6
                row cache lock                 1                                           100.0
                slave exit                     4  50.0                                50.0
                switch logfile command         2                                           100.0
                undo segment extension         6  33.3                    33.3  16.7  16.7
                utl_file I/O                 100 100.0
                write complete waits          19                                 5.3  94.7
                DIAG idle wait              7164                                     100.0
                JOX Jit Process Sleep        231                                           100.0
                PL/SQL lock timer            246                                       4.1  95.9
                PX Deq Credit: send blkd     194  74.7         3.6  12.9   3.6         2.1   3.1
                PX Deq: Execute Reply       5973  79.2   5.3   4.8   4.2   2.6   1.8   2.1    .0
                PX Deq: Execution Msg       6761  83.0   5.5   2.1   3.6   3.0   1.5    .9    .3
                PX Deq: Join ACK             352  93.2   3.1   2.6    .9    .3
                PX Deq: Msg Fragment          46 100.0
                PX Deq: Parse Reply          352  83.0   2.3   2.0   1.4   8.2   1.1   2.0
                PX Deq: Table Q Normal       535  74.8         3.0   3.0   1.5   3.0   1.5  13.3
                PX Deq: Table Q Sample        48   4.2  22.9  22.9                    16.7  33.3
                PX Idle Wait                 349    .6                                52.1  47.3
                SQL*Net message from clien 394.9  38.0  26.5   7.0  10.7  10.4   1.0   4.3   2.1
                Space Manager: slave idle   6462    .2    .1    .1                .2   6.8  92.6
                Wait Event Histogram               DB/Inst: PRD/PRD  Snaps: 38744-38748
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> % of Waits: value of .0 indicates value was <.05%; value of null is truly 0
                -> % of Waits: column heading of <=1s is truly <1024ms, >1s is truly >=1024ms
                -> Ordered by Event (idle events last)
                
                                                                    % of Waits
                                                 -----------------------------------------------
                                           Total
                Event                      Waits  <1ms  <2ms  <4ms  <8ms <16ms <32ms  <=1s   >1s
                -------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
                Streams AQ: qmn coordinato  1408  62.7                                      37.3
                Streams AQ: qmn slave idle  1042                                           100.0
                Streams AQ: waiting for me  8641    .5                            .0   2.8  96.7
                Streams AQ: waiting for ti   102   7.8                                46.1  46.1
                class slave wait              50 100.0
                i/o slave wait               26K  99.0          .0    .0    .0    .0    .9
                jobq slave wait             7283    .1    .0    .1    .0    .0    .0  99.8
                pmon timer                  1335   1.1                      .2    .4   7.0  91.2
                rdbms ipc message          133.5  15.8   7.3   5.4   2.0  42.5   1.0  12.2  13.9
                single-task message           86                                     100.0
                smon timer                    89   2.2                           1.1  13.5  83.1
                          -------------------------------------------------------------
                
                Wait Event Histogram Detail (64 msec to 2 sec)DB/Inst: PRD/PRD  Snaps:
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> Units for % of Total Waits:
                   ms is milliseconds
                   s is 1024 milliseconds (approximately 1 second)
                -> % of Total Waits: total waits for all wait classes, including Idle
                -> % of Total Waits: value of .0 indicates value was <.05%;
                   value of null is truly 0
                -> Ordered by Event (only non-idle events are displayed)
                
                                                                 % of Total Waits
                                                 -----------------------------------------------
                                           Waits
                                           64ms
                Event                      to 2s <32ms <64ms <1/8s <1/4s <1/2s   <1s   <2s  >=2s
                -------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
                Backup: MML commit backup      1  66.7  33.3
                Backup: MML create a backu     2  33.3  66.7
                Backup: MML initialization     2              50.0  50.0
                Backup: MML write backup p    30  99.9    .1    .0
                Disk file operations I/O       6 100.0    .0          .0    .0    .0
                Log archive I/O              263  97.2    .2    .6   1.7    .3
                PX Deq: Signal ACK EXT         2  99.5    .5
                PX Deq: Table Q Get Keys       4  65.6   9.4   3.1                          21.9
                RMAN Tape slave I/O            1 100.0    .0
                RMAN backup & recovery I/O    11  83.6  14.9   1.5
                SQL*Net break/reset to cli    11  99.6                .4
                SQL*Net message from dblin   215  99.8    .1    .0    .0    .0    .0    .0    .0
                SQL*Net more data from dbl     7 100.0    .0          .0    .0    .0
                buffer busy waits             42  87.4          .0    .2    .8    .4    .5  10.7
                control file parallel writ    52  97.9    .9    .8    .3
                control file sequential re    19 100.0    .0          .0
                control file single write    205  29.6   1.4  11.7  14.4  33.7   9.3
                cursor: pin S wait on X       51  63.8  19.1   7.1   9.9
                db file parallel read          2  96.6   3.4
                db file parallel write      8103  85.9   7.1   3.9   1.8    .8    .3    .1    .1
                db file scattered read      2159  98.6   1.2    .1    .0    .0    .0
                db file sequential read     4258  99.3    .2    .3    .2    .0    .0    .0
                db file single write           2  75.0        25.0
                direct path read            1613  99.4    .5    .1    .0    .0    .0
                direct path read temp        159  78.3   4.8   6.5   8.7   1.6
                direct path sync             224  75.4   9.5  12.2   2.5    .4
                direct path write             18  99.8    .1    .0    .0    .0
                direct path write temp     10.9K  98.0    .4   1.0    .7    .0    .0    .0    .0
                enq: CF - contention           1  83.3              16.7
                enq: HW - contention           1  87.5  12.5
                enq: JD - contention           1                                      50.0  50.0
                enq: JS - queue lock           1  80.0  20.0
                enq: KO - fast object chec     1  80.0              20.0
                enq: RO - fast object reus    31  53.4   8.0  12.5   3.4   5.7   4.5   1.1  11.4
                enq: TM - contention           9        20.0  10.0        30.0  30.0        10.0
                enq: TX - index contention     1  88.9  11.1
                enq: TX - row lock content     2  90.0         5.0                     5.0
                enq: UL - contention           1  42.9                          14.3        42.9
                imm op                        22   4.3   8.7        17.4   4.3  65.2
                kksfbc child completion        2       100.0
                ksdxexeotherwait               1  66.7  33.3
                library cache lock             3  50.0  50.0
                local write wait              19  76.8   5.2   1.9   1.3   1.9   1.9        11.0
                log buffer space              50    .2          .8    .4   1.3   2.9   5.0  89.3
                log file parallel write      835  99.2    .3    .2    .1    .1    .0    .0    .1
                log file sequential read      19  95.6   4.4
                log file switch (private s     2        50.0        50.0
                log file sync               1351  65.5   4.3   1.5   1.7   1.7   1.2   1.9  22.2
                os thread startup            188             100.0
                read by other session          9  99.3    .5                .2
                recovery area: computing b     1                               100.0
                recovery area: computing d     1                   100.0
                recovery area: computing o     1  60.0                                20.0  20.0
                slave exit                     2  50.0                    50.0
                undo segment extension         1  83.3  16.7
                write complete waits          18   5.3               5.3  73.7  15.8
                          -------------------------------------------------------------
                
                Wait Event Histogram Detail (4 sec to 2 min)DB/Inst: PRD/PRD  Snaps: 38
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> Units for % of Total Waits:
                   s is 1024 milliseconds (approximately 1 second)
                   m is 64*1024 milliseconds (approximately 67 seconds or 1.1 minutes)
                -> % of Total Waits: total waits for all wait classes, including Idle
                -> % of Total Waits: value of .0 indicates value was <.05%;
                   value of null is truly 0
                -> Ordered by Event (only non-idle events are displayed)
                
                                                                 % of Total Waits
                                                 -----------------------------------------------
                                           Waits
                                            4s
                Event                      to 2m   <2s   <4s   <8s  <16s  <32s  < 1m  < 2m  >=2m
                -------------------------- ----- ----- ----- ----- ----- ----- ----- ----- -----
                PX Deq: Table Q Get Keys       7  78.1        21.9
                SQL*Net message from dblin    34 100.0    .0    .0          .0                .0
                buffer busy waits            236  89.3    .9   2.0   2.3   3.7   1.8
                db file parallel write        43  99.9    .1    .0    .0    .0
                direct path write temp         2 100.0    .0    .0
                enq: JD - contention           1  50.0                    50.0
                enq: RO - fast object reus    10  88.6   1.1   3.4   3.4   2.3   1.1
                enq: TM - contention           1  90.0  10.0
                enq: UL - contention           3  57.1  14.3  28.6
                latch: In memory undo latc    26  86.2   1.1   2.7   5.9   3.7    .5
                local write wait              17  89.0    .6         2.6   1.9   5.8
                log buffer space             427  10.7   9.6  12.1  26.2  22.8  18.6
                log file parallel write      167  99.9    .0    .0    .0    .0    .0
                log file switch completion    32        12.5  40.6  40.6   3.1   3.1
                log file sync               2429  77.8   2.7   3.3   5.1   5.7   4.9    .6
                recovery area: computing o     1  80.0        20.0
                row cache lock                 1             100.0
                switch logfile command         2                          50.0  50.0
                          -------------------------------------------------------------
                
                Wait Event Histogram Detail (4 min to 1 hr)DB/Inst: PRD/PRD  Snaps: 387
                -> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
                -> Units for % of Total Waits:
                   m is 64*1024 milliseconds (approximately 67 seconds or 1.1 minutes)
                   h is 4096*1024 milliseconds (approximately 70 minutes or 1.17 hours)
                -> % of Total Waits: total waits for all wait classes, including Idle
                -> % of Total Waits: value of .0 indicates value was <.05%;
                   value of null is truly 0
                -> Ordered by Event (only non-idle events are displayed)
                
                                                              % of Total Waits
                                                 -----------------------------------------
                                           Waits
                                             4m
                Event                      to 1h   <2m   <4m   <8m <1/4h <1/2h  < 1h  >=1h
                -------------------------- ----- ----- ----- ----- ----- ----- ----- -----
                SQL*Net message from dblin     2 100.0                      .0    .0
                          -------------------------------------------------------------
                Rgds
                Abhay
                • 20. Re: Log Buffer
                  996125
                  This would seem so looking at AWR and other diagnostics, but whenever IO write speed goes low we see this issue. PS below 10298 event for LGWR.

                  Below o/p could be argued to be - application may not be generating bigger redo data, however this is the period when bulky jobs run & storage reports show nearly 100% disk usage on redo FS.
                  Bad Period: Less than 3MBPS (Some times even less than 1.5MBPS)
                  
                  *** 2013-03-12 11:07:55.135
                  Warning: log write elapsed time 1535ms, size 3234KB
                  
                  *** 2013-03-12 11:07:55.816
                  Warning: log write elapsed time 678ms, size 1136KB
                  
                  *** 2013-03-12 11:07:57.051
                  Warning: log write elapsed time 1232ms, size 3821KB
                  
                  *** 2013-03-12 11:07:58.173
                  Warning: log write elapsed time 737ms, size 3330KB
                  
                  *** 2013-03-12 11:08:00.577
                  Warning: log write elapsed time 2098ms, size 5567KB
                  
                  *** 2013-03-12 11:08:02.285
                  Warning: log write elapsed time 1541ms, size 3711KB
                  
                  *** 2013-03-12 11:08:04.893
                  Warning: log write elapsed time 2226ms, size 3727KB
                  
                  *** 2013-03-12 11:08:08.152
                  Warning: log write elapsed time 2882ms, size 4821KB
                  
                  *** 2013-03-12 11:08:12.672
                  Warning: log write elapsed time 4102ms, size 8549KB
                  
                  *** 2013-03-12 11:08:13.303
                  Warning: log write elapsed time 630ms, size 830KB
                  
                  *** 2013-03-12 11:08:15.948
                  Warning: log write elapsed time 2641ms, size 4168KB
                  
                  *** 2013-03-12 11:08:16.559
                  Warning: log write elapsed time 609ms, size 894KB
                  
                  *** 2013-03-12 11:08:18.814
                  Warning: log write elapsed time 2252ms, size 3358KB
                  
                  *** 2013-03-12 11:08:19.461
                  Warning: log write elapsed time 645ms, size 986KB
                  
                  *** 2013-03-12 11:08:21.673
                  Warning: log write elapsed time 2208ms, size 4393KB
                  
                  *** 2013-03-12 11:08:23.133
                  Warning: log write elapsed time 1348ms, size 2804KB
                  
                  *** 2013-03-12 11:08:24.191
                  Warning: log write elapsed time 1056ms, size 1552KB
                  
                  
                  Good Period: Nearly 5-8MBPS
                  
                  Warning: log write elapsed time 943ms, size 8881KB
                  
                  *** 2013-03-12 12:32:03.253
                  Warning: log write elapsed time 1615ms, size 8255KB
                  
                  *** 2013-03-12 12:32:04.389
                  Warning: log write elapsed time 943ms, size 4991KB
                  
                  *** 2013-03-12 12:32:05.064
                  Warning: log write elapsed time 671ms, size 2900KB
                  
                  *** 2013-03-12 12:32:06.179
                  Warning: log write elapsed time 1107ms, size 9487KB
                  
                  *** 2013-03-12 12:32:07.386
                  Warning: log write elapsed time 981ms, size 6529KB
                  
                  *** 2013-03-12 12:32:08.974
                  Warning: log write elapsed time 1211ms, size 7251KB
                  
                  *** 2013-03-12 12:32:09.954
                  Warning: log write elapsed time 975ms, size 5806KB
                  
                  *** 2013-03-12 12:32:11.366
                  Warning: log write elapsed time 1255ms, size 4058KB
                  • 21. Re: Log Buffer
                    Paul R
                    100% disk usage in what respect ? activity or space ?

                    Edited by: Paul R on 15-Mar-2013 01:22
                    • 22. Re: Log Buffer
                      996125
                      Well i think the context is performance, so the obvious deduction should be activity rather than space.

                      Rgds
                      Abhay
                      • 23. Re: Log Buffer
                        Hemant K Chitale
                        What sort of storage and filesystem are in use ?

                        Are you running any other services / applications (i.e. other than the oracle database itself) on the same server ?


                        CPU usage doesn't seem to be high yet there's quite a big difference between 'log file sync' and 'log file parallel write'.


                        Hemant K Chitale
                        • 24. Re: Log Buffer
                          996125
                          Hemant K Chitale wrote:
                          What sort of storage and filesystem are in use ?

                          Are you running any other services / applications (i.e. other than the oracle database itself) on the same server ?


                          CPU usage doesn't seem to be high yet there's quite a big difference between 'log file sync' and 'log file parallel write'.


                          Hemant K Chitale
                          SAN storage from IBM, RAID level 5 (i know redo are not best candidate on RAID 5) - change to RAID 10/1 is being implemented.

                          On the HOST no other application except this DB, but on storage - possibly yes as its a virtualized storage UNIT of 100TB and 20TB is given for this DB. But point is whenever the heavy jobs run, the issue is seen - hence i am discounting if other hosts connecting to this SAN storage might be causing a spoil sport.

                          Your CPU observation is quite right, this is where I first thought it may be the COMMIT rate that is causing spoil sport - commit rate was about 60-100/s & when we reduced to 5-10/s by using application profile options, to my surprise, the situation worsened a slightly. This was when i started digging deep and found slower IO rate when this problem caused pains, hence to mitigate - lowered the log buffer after which we are in a very thin acceptable UI response.

                          I am still unable to find why there is a large discrepancy between avg wait times of log writer vs log file sync. However if look at log file parallel write time, out of 3600 secs this event has waited 3000+ secs - if whatever is said in http://tonyhasler.wordpress.com/2011/07/24/log-file-sync-and-log-file-parallel-write-part-2/ is true about odity of serialization in flushing out data from public redo strands, then 3000 secs out of 3600 looks significant. Also the author mentions of one more important point
                          Private redo strands do not exist in instances within a RAC cluster. In a non-RAC environment each transaction gets its own redo strand (subject to availability).
                          These strands are used in combination with in-memory undo (IMU) to reduce the amount of data that is logged but more importantly to reduce latching conflicts;
                          data is normally copied from a private redo strand only at commit time. Data will also be copied out if the private redo strand fills up before a commit is issued.
                          These private redo strands are allocated from shared pool.
                          We have about 500+ private redo strands, not sure why we have so much (possibly because we have a high CPU, very high settings on processes, sessions, transactions) - on a non busy period when i checked with the query Jonathan Lewis pointed me to get a understanding of private and public redo strands, i note we had 4 public and about 550 private redo strands and atlleast 160+ being in use. So a hypothesis i have is, small transactions are getting different private redo strands and on commit these have to be copied over and possibly taking time? Note we have 10-50 jobs generating good amount of redo and 10-100 UI sessions generating small transactions. It may be a overhead to have so many private redo strands?


                          Rgds
                          Abhay
                          • 25. Re: Log Buffer
                            Paul R
                            oh really.

                            so you're hitting 100% activity on your redo log storage and wonder where the performance problem is ?

                            i think the log file sync includes the log file parallel write time. i could be wrong. no doubt people will be lining up to point this out.

                            Edited by: Paul R on 15-Mar-2013 04:43
                            • 26. Re: Log Buffer
                              996125
                              yes only problem is AWR reports a lot less avg and absolute time spent on log file parallel write when compared to log file sync (particularly folks will be interested in avg time spent).
                              • 27. Re: Log Buffer
                                Rob_J
                                Hi,

                                Maybe it's been covered or I'm over-simplifying the situation but as I see it you have:

                                1. Very slow response times for writing from the log buffer to the REDO logs
                                2. Your REDO logs are on slow disks (RAID 5)
                                3. Your storage is shared with other applications, thus potentially causing contention

                                The above 3 points should be taken care of ASAP, in my opnion. Even if the rest of the database remains on the shared storage, just get a new drive for your REDO logs. I'm sure you don't need much space at all?

                                How large are your REDO logs and how often are they switching, just out of interest?

                                Also, is the core where the LGWR is running on being thrashed? The box as a whole might not be over worked but one core could be.

                                Rob
                                • 28. Re: Log Buffer
                                  Rob_J
                                  I just read this article which I thought was quite interesting about [url http://christianbilien.wordpress.com/2008/02/12/the-%E2%80%9Clog-file-sync%E2%80%9D-wait-event-is-not-always-spent-waiting-for-an-io/]Log File Sync which also mentions about checking the CPU run queues as that can be the cause of the wait and not necessarily I/O.
                                  • 29. Re: Log Buffer
                                    Rob_J
                                    Paul R wrote:
                                    i think the log file sync includes the log file parallel write time. i could be wrong. no doubt people will be lining up to point this out.
                                    Interesting point, Paul. Sounds like the docs agree with you?
                                    When a user session commits, the session's redo information needs to be flushed to the redo logfile. The user session will post the LGWR to write the log buffer to the redo log file. When the LGWR has finished writing, it will post the user session.
                                    Wait Time: The wait time includes the writing of the log buffer and the post.
                                    Taken from [url http://docs.oracle.com/cd/E11882_01/server.112/e25513/waitevents003.htm#sthref4014]Oracle description of wait events