Bonjour à tous,

Je cherche en ce moment à exploiter les rapports AWR de ma base pour améliorer ses performances.

Seulement voilà, un détail me chiffonne: les valeurs de certaines statistiques communes aux sections Time Model Statistics (TMS) et Instance Activity Statistics (IAS) diffèrent.

Je sais que TMS est affiché en secondes, alors que certaines stats de IAS (comme DB CPU) sont en centisecondes, mais même en faisant la conversion, le compte n'y est pas.

Exemple: (couleur verte pour les stats TSM concernées, rouge pour IAS)

Code : Sélectionner tout - Visualiser dans une fenêtre à part
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WORKLOAD REPOSITORY report for

DB Name         DB Id    Instance     Inst Num Release     Cluster Host
------------ ----------- ------------ -------- ----------- ------- ------------
PROD            14612696 prod                1 10.1.0.3.0  NO      

              Snap Id      Snap Time      Sessions Curs/Sess
            --------- ------------------- -------- ---------
Begin Snap:     29861 21-Jun-11 07:00:36    13,106        .2
  End Snap:     29864 21-Jun-11 10:01:01    13,113        .2
   Elapsed:              180.41 (mins)
   DB Time:              248.37 (mins)

Cache Sizes (end)
~~~~~~~~~~~~~~~~~
               Buffer Cache:     1,248M      Std Block Size:         8K
           Shared Pool Size:     1,264M          Log Buffer:     1,024K

Load Profile
~~~~~~~~~~~~                            Per Second       Per Transaction
                                   ---------------       ---------------
                  Redo size:            112,303.65             25,632.10
              Logical reads:              8,316.25              1,898.09
              Block changes:                283.46                 64.70
             Physical reads:                 88.91                 20.29
            Physical writes:                 16.93                  3.86
                 User calls:                916.65                209.22
                     Parses:                393.85                 89.89
                Hard parses:                 10.53                  2.40
                      Sorts:                 32.07                  7.32
                     Logons:                  3.28                  0.75
                   Executes:                641.92                146.51
               Transactions:                  4.38

  % Blocks changed per Read:    3.41    Recursive Call %:    57.23
 Rollback per transaction %:   12.51       Rows per Sort:    28.07

Instance Efficiency Percentages (Target 100%)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            Buffer Nowait %:  100.00       Redo NoWait %:  100.00
            Buffer  Hit   %:   98.93    In-memory Sort %:  100.00
            Library Hit   %:   98.63        Soft Parse %:   97.33
         Execute to Parse %:   38.65         Latch Hit %:   99.90
Parse CPU to Parse Elapsd %:   84.64     % Non-Parse CPU:   89.65

 Shared Pool Statistics        Begin    End
                              ------  ------
             Memory Usage %:   94.04   92.81
    % SQL with executions>1:   67.85   81.60
  % Memory for SQL w/exec>1:   64.64   60.31

Top 5 Timed Events
~~~~~~~~~~~~~~~~~~                                        % Total
Event                                 Waits    Time (s)   DB Time     Wait Class
------------------------------ ------------ ----------- --------- --------------
class slave wait                        125      10,650     71.47          Other
db file sequential read             825,581       7,483     50.21       User I/O
CPU time                                          6,135     41.17
log file sync                        46,429         926      6.21         Commit
log file parallel write             103,130         638      4.28     System I/O
          -------------------------------------------------------------
Wait Events  DB/Inst: PROD/prod  Snaps: 29861-29864
-> s  - second
-> cs - centisecond -     100th of a second
-> ms - millisecond -    1000th of a second
-> us - microsecond - 1000000th of a second
-> ordered by wait time desc, waits desc (idle events last)

                                                                   Avg
                                                    Total Wait    wait     Waits
Event                              Waits   Timeouts   Time (s)    (ms)      /txn
--------------------------- ------------ ---------- ---------- ------- ---------
class slave wait                     125         91     10,650   85202       0.0
db file sequential read          825,581          0      7,483       9      17.4
log file sync                     46,429        359        926      20       1.0
log file parallel write          103,130          0        638       6       2.2
control file parallel write        8,316          0        221      27       0.2
db file scattered read            20,583          0        183       9       0.4
db file parallel write            28,210          0        172       6       0.6
control file sequential rea       17,786          0        134       8       0.4
latch: library cache              36,210          0        122       3       0.8
SQL*Net more data to client    4,693,287          0         56       0      99.0
log file sequential read           1,032          0         51      49       0.0
log buffer space                     206          2         50     244       0.0
latch: shared pool                47,426          0         32       1       1.0
control file single write          1,629          0         24      15       0.0
db file parallel read                424          0         19      45       0.0
master wait                           42          2         10     230       0.0
SQL*Net message to client      7,941,071          0          9       0     167.4
read by other session                 12          0          8     662       0.0
enq: CF - contention                   7          1          7    1019       0.0
buffer busy waits                    519          1          3       7       0.0
enq: HW - contention                 464          0          3       7       0.0
SQL*Net more data from clie      141,950          0          2       0       3.0
SQL*Net break/reset to clie       11,352          0          1       0       0.2
library cache pin                      2          0          1     441       0.0
log file switch completion             8          0          0      53       0.0
rdbms ipc reply                      482          0          0       1       0.0
latch free                            19          0          0      18       0.0
recovery area: computing ob            4          0          0      76       0.0
process startup                       10          0          0      20       0.0
latch: session allocation            873          0          0       0       0.0
direct path read                     152          0          0       1       0.0
LGWR wait for redo copy              644          1          0       0       0.0
enq: TX - index contention             2          0          0      23       0.0
wait list latch free                   3          0          0      15       0.0
direct path write                 52,249          0          0       0       1.1
latch: In memory undo latch            4          0          0       7       0.0
ksfd: async disk IO               10,621          0          0       0       0.2
latch: row cache objects              34          0          0       1       0.0
latch: library cache pin              19          0          0       0       0.0
latch: cache buffers chains           37          0          0       0       0.0
log file single write                  8          0          0       1       0.0
enq: TX - row lock contenti            1          0          0       4       0.0
undo segment extension             4,264      4,245          0       0       0.1
latch: library cache lock             10          0          0       0       0.0
recovery area: computing ba            2          0          0       0       0.0
recovery area: computing dr            2          0          0       0       0.0
recovery area: computing ap            2          0          0       0       0.0
latch: cache buffers lru ch            7          0          0       0       0.0
latch: redo writing                    2          0          0       0       0.0
latch: redo allocation                 2          0          0       0       0.0
buffer deadlock                        1          1          0       0       0.0
SQL*Net message from client    7,941,061          0    532,984      67     167.4
jobq slave wait                   10,517     10,341     31,498    2995       0.2
ASM background timer               2,194          0     10,526    4798       0.0
queue messages                     2,121      2,097     10,518    4959       0.0
Queue Monitor Wait                   351        351     10,506   29931       0.0
virtual circuit status               359        359     10,502   29254       0.0
wait for unread message on        10,496     10,420     10,452     996       0.2
wakeup time manager                   67         42     10,276  153368       0.0
          -------------------------------------------------------------

Background Wait Events  DB/Inst: PROD/prod  Snaps: 29861-29864
-> ordered by wait time desc, waits desc (idle events last)

                                                                   Avg
                                                    Total Wait    wait     Waits
Event                              Waits   Timeouts   Time (s)    (ms)      /txn
--------------------------- ------------ ---------- ---------- ------- ---------
log file parallel write          103,110          0        638       6       2.2
control file parallel write        8,090          0        221      27       0.2
db file parallel write            28,210          0        172       6       0.6
control file sequential rea        9,274          0         72       8       0.2
log file sequential read           1,032          0         51      49       0.0
control file single write          1,556          0         24      15       0.0
enq: CF - contention                   7          1          7    1019       0.0
master wait                           19          2          7     358       0.0
db file scattered read               214          0          2      11       0.0
buffer busy waits                    120          0          0       2       0.0
process startup                       10          0          0      20       0.0
direct path read                      96          0          0       1       0.0
rdbms ipc reply                      467          0          0       0       0.0
LGWR wait for redo copy              644          1          0       0       0.0
ksfd: async disk IO                1,994          0          0       0       0.0
log file single write                  8          0          0       1       0.0
direct path write                     96          0          0       0       0.0
latch: redo writing                    2          0          0       0       0.0
latch: cache buffers lru ch            4          0          0       0       0.0
latch: redo allocation                 2          0          0       0       0.0
latch: cache buffers chains            1          0          0       0       0.0
latch: session allocation              6          0         -0      -1       0.0
latch: shared pool                    61          0         -0      -0       0.0
latch: library cache                  18          0         -1     -32       0.0
log buffer space                       1          0         -2   -1630       0.0
db file sequential read            1,871          0         -7      -4       0.0
rdbms ipc message                 86,591     33,416    110,549    1277       1.8
ASM background timer               2,194          0     10,526    4798       0.0
Queue Monitor Wait                   351        351     10,506   29931       0.0
smon timer                         2,804          0     10,427    3719       0.1
wakeup time manager                   67         42     10,276  153368       0.0
          -------------------------------------------------------------

Time Model Statistics  DB/Inst: PROD/prod  Snaps: 29861-29864
-> ordered by Time (seconds) desc

                                                       Time      % Total
Statistic Name                                     (seconds)     DB Time
--------------------------------------------- -------------- -----------
background elapsed time                            38,490.24      258.28
DB time                                            14,902.42      100.00
sql execute elapsed time                            7,626.68       51.18
DB CPU                                              6,134.99       41.17
Java execution elapsed time                         2,775.55       18.62
parse time elapsed                                    825.42        5.54
hard parse elapsed time                               575.92        3.86
PL/SQL execution elapsed time                         526.67        3.53
connection management call elapsed time               425.88        2.86
inbound PL/SQL rpc elapsed time                       240.21        1.61
PL/SQL compilation elapsed time                        89.01         .60
background cpu time                                    57.12         .38
hard parse (sharing criteria) elapsed time              8.16         .05
sequence load elapsed time                              4.85         .03
hard parse (bind mismatch) elapsed time                  .30         .00
failed parse elapsed time                                .00         .00
failed parse (out of shared memory) elapsed t            .00         .00
          -------------------------------------------------------------

Operating System Statistics  DB/Inst: PROD/prod  Snaps: 29861-29864

                  No data exists for this section of the report.
          -------------------------------------------------------------

Service Statistics  DB/Inst: PROD/prod  Snaps: 29861-29864
-> ordered by DB Time

                                                             Physical    Logical
Service Name                      DB Time (s)   DB CPU (s)      Reads      Reads
-------------------------------- ------------ ------------ ---------- ----------
SYS$USERS                             8,539.1      1,279.4    855,455 ##########
prod                                  6,376.7      4,867.6     99,064 ##########
SYS$BACKGROUND                            0.0          0.0      7,522    454,550
prodXDB                                   0.0          0.0          0          0
          -------------------------------------------------------------

Service Wait Class Stats  DB/Inst: PROD/prod  Snaps: 29861-29864
-> Wait Class info for services in the Service Statistics section.
-> Total Waits and Time Waited displayed for the following wait
   classes:  User I/O, Concurrency, Administrative, Network
-> Time Waited (Wt Time) in centisecond (100th of a second)

Service Name
----------------------------------------------------------------
 User I/O  User I/O  Concurcy  Concurcy     Admin     Admin   Network   Network
Total Wts   Wt Time Total Wts   Wt Time Total Wts   Wt Time Total Wts   Wt Time
--------- --------- --------- --------- --------- --------- --------- ---------
SYS$USERS
   833039    666714      8303      3409         0         0   6900416      5930
prod
    60303     96863     28016      9131         0         0   5770035       802
SYS$BACKGROUND
     5658      5625       469       106         0         0         0         0
          -------------------------------------------------------------


Instance Activity Stats  DB/Inst: PROD/prod  Snaps: 29861-29864

Statistic                                     Total     per Second     per Trans
-------------------------------- ------------------ -------------- -------------
CPU used by this session                    632,116           58.4          13.3
CPU used when call started                  632,190           58.4          13.3
CR blocks created                             6,896            0.6           0.2
Cached Commit SCN referenced                 78,956            7.3           1.7
Commit SCN cached                                26            0.0           0.0
DB time                                   4,795,658          443.0         101.1
DBWR checkpoint buffers written              82,902            7.7           1.8
DBWR checkpoints                                  2            0.0           0.0
DBWR object drop buffers written                  0            0.0           0.0
DBWR parallel query checkpoint b                  0            0.0           0.0
DBWR revisited being-written buf                  0            0.0           0.0
DBWR tablespace checkpoint buffe                  0            0.0           0.0
DBWR thread checkpoint buffers w                  0            0.0           0.0
DBWR transaction table writes                   588            0.1           0.0
DBWR undo block writes                       86,500            8.0           1.8
DDL statements parallelized                       0            0.0           0.0
DFO trees parallelized                            0            0.0           0.0
DML statements parallelized                       0            0.0           0.0
IMU CR rollbacks                              4,678            0.4           0.1
IMU Flushes                                   7,334            0.7           0.2
IMU Redo allocation size                 17,414,416        1,608.8         367.2
IMU bind flushes                                 26            0.0           0.0
IMU commits                                  36,428            3.4           0.8
IMU contention                                   64            0.0           0.0
IMU ktichg flush                                147            0.0           0.0
IMU pool not allocated                            2            0.0           0.0
IMU recursive-transaction flush                   9            0.0           0.0
IMU undo allocation size                194,349,640       17,954.7       4,098.0
IMU- failed to get a private str                  2            0.0           0.0
Misses for writing mapping                        0            0.0           0.0
OS Involuntary context switches                   0            0.0           0.0
OS Page faults                                    0            0.0           0.0
OS Page reclaims                                  0            0.0           0.0
OS System time used                               0            0.0           0.0
OS User time used                                 0            0.0           0.0
OS Voluntary context switches                     0            0.0           0.0
PX local messages recv'd                          0            0.0           0.0
PX local messages sent                            0            0.0           0.0
Parallel operations not downgrad                  0            0.0           0.0
SQL*Net roundtrips to/from clien          7,832,101          723.6         165.1
active txn count during cleanout             11,890            1.1           0.3
application wait time                           135            0.0           0.0
background checkpoints completed                  2            0.0           0.0
background checkpoints started                    2            0.0           0.0
background timeouts                          33,733            3.1           0.7
branch node splits                                3            0.0           0.0
buffer is not pinned count               45,444,639        4,198.3         958.2
buffer is pinned count                   80,441,282        7,431.4       1,696.1
bytes received via SQL*Net from       2,384,908,935      220,325.6      50,287.0
bytes sent via SQL*Net to client     14,219,129,697    1,313,609.1     299,817.2
calls to get snapshot scn: kcmgs          9,804,086          905.7         206.7
calls to kcmgas                             171,535           15.9           3.6
calls to kcmgcs                              12,913            1.2           0.3
change write time                             6,792            0.6           0.1
cleanout - number of ktugct call             13,173            1.2           0.3
cleanouts and rollbacks - consis              2,590            0.2           0.1
cleanouts only - consistent read              1,042            0.1           0.0
cluster key scan block gets                  68,417            6.3           1.4
cluster key scans                            43,087            4.0           0.9
commit cleanout failures: block                 825            0.1           0.0
Instance Activity Stats  DB/Inst: PROD/prod  Snaps: 29861-29864

Statistic                                     Total     per Second     per Trans
-------------------------------- ------------------ -------------- -------------
commit cleanout failures: buffer                  0            0.0           0.0
commit cleanout failures: callba                  6            0.0           0.0
commit cleanout failures: cannot                 22            0.0           0.0
commit cleanouts                            197,106           18.2           4.2
commit cleanouts successfully co            196,253           18.1           4.1
commit txn count during cleanout              6,581            0.6           0.1
concurrency wait time                        12,636            1.2           0.3
consistent changes                          123,408           11.4           2.6
consistent gets                          85,556,854        7,904.0       1,804.0
consistent gets - examination            38,464,122        3,553.4         811.0
consistent gets direct                          100            0.0           0.0
consistent gets from cache               85,556,753        7,904.0       1,804.0
current blocks converted for CR                   3            0.0           0.0
cursor authentications                       38,059            3.5           0.8
data blocks consistent reads - u             80,897            7.5           1.7
db block changes                          3,068,353          283.5          64.7
db block gets                             4,462,187          412.2          94.1
db block gets direct                         29,061            2.7           0.6
db block gets from cache                  4,433,126          409.6          93.5
deferred (CURRENT) block cleanou             89,988            8.3           1.9
dirty buffers inspected                      52,478            4.9           1.1
enqueue conversions                           5,166            0.5           0.1
enqueue releases                            424,473           39.2           9.0
enqueue requests                            424,461           39.2           9.0
enqueue timeouts                                  1            0.0           0.0
enqueue waits                                   473            0.0           0.0
exchange deadlocks                                1            0.0           0.0
execute count                             6,948,445          641.9         146.5
frame signature mismatch                          0            0.0           0.0
free buffer inspected                     1,077,039           99.5          22.7
free buffer requested                     1,082,598          100.0          22.8
heap block compress                          16,039            1.5           0.3
hot buffers moved to head of LRU            511,680           47.3          10.8
immediate (CR) block cleanout ap              3,632            0.3           0.1
immediate (CURRENT) block cleano             48,338            4.5           1.0
index fast full scans (direct re                  0            0.0           0.0
index fast full scans (full)                  9,215            0.9           0.2
index fast full scans (rowid ran                  0            0.0           0.0
index fetch by key                       12,590,897        1,163.2         265.5
index scans kdiixs1                       7,154,211          660.9         150.9
java call heap collected bytes        2,326,836,872      214,960.7      49,062.5
java call heap collected count           73,951,711        6,831.9       1,559.3
java call heap gc count                       4,669            0.4           0.1
java call heap live object count             11,302            1.0           0.2
java call heap live object count             61,085            5.6           1.3
java call heap live size                  8,031,176          742.0         169.3
java call heap live size max              9,020,272          833.3         190.2
java call heap object count                  18,280            1.7           0.4
java call heap object count max             119,236           11.0           2.5
java call heap total size                11,796,480        1,089.8         248.7
java call heap total size max            11,796,480        1,089.8         248.7
java call heap used size                  8,398,736          775.9         177.1
java call heap used size max             11,603,632        1,072.0         244.7
leaf node 90-10 splits                          367            0.0           0.0
leaf node splits                              1,271            0.1           0.0
logons cumulative                            35,536            3.3           0.8
messages received                            79,692            7.4           1.7
messages sent                                79,692            7.4           1.7
no buffer to keep pinned count                    0            0.0           0.0
no work - consistent read gets           38,294,305        3,537.8         807.5
Instance Activity Stats  DB/Inst: PROD/prod  Snaps: 29861-29864

Statistic                                     Total     per Second     per Trans
-------------------------------- ------------------ -------------- -------------
opened cursors cumulative                 4,180,338          386.2          88.1
parse count (failures)                          129            0.0           0.0
parse count (hard)                          113,930           10.5           2.4
parse count (total)                       4,263,193          393.9          89.9
parse time cpu                               63,486            5.9           1.3
parse time elapsed                           75,010            6.9           1.6
physical read IO requests                   856,540           79.1          18.1
physical reads                              962,433           88.9          20.3
physical reads cache                        962,281           88.9          20.3
physical reads cache prefetch               115,710           10.7           2.4
physical reads direct                           152            0.0           0.0
physical reads direct (lob)                      56            0.0           0.0
physical reads direct temporary                   0            0.0           0.0
physical reads prefetch warmup                    0            0.0           0.0
physical write IO requests                  103,975            9.6           2.2
physical writes                             183,247           16.9           3.9
physical writes direct                       29,157            2.7           0.6
physical writes direct (lob)                 29,001            2.7           0.6
physical writes direct temporary                  0            0.0           0.0
physical writes from cache                  154,090           14.2           3.3
physical writes non checkpoint              153,688           14.2           3.2
pinned buffers inspected                        105            0.0           0.0
prefetch warmup blocks aged out                   0            0.0           0.0
prefetched blocks aged out befor                 59            0.0           0.0
process last non-idle time       ################## ############## #############
queries parallelized                              0            0.0           0.0
recursive calls                          13,277,702        1,226.6         280.0
recursive cpu usage                         408,029           37.7           8.6
redo blocks written                       2,477,742          228.9          52.2
redo buffer allocation retries                  212            0.0           0.0
redo entries                              1,425,989          131.7          30.1
redo log space requests                           8            0.0           0.0
redo log space wait time                         46            0.0           0.0
redo ordering marks                          85,050            7.9           1.8
redo size                             1,215,628,112      112,303.7      25,632.1
redo synch time                              94,783            8.8           2.0
redo synch writes                            42,590            3.9           0.9
redo wastage                             13,740,880        1,269.4         289.7
redo write time                              65,380            6.0           1.4
redo writer latching time                         7            0.0           0.0
redo writes                                  51,475            4.8           1.1
rollback changes - undo records              20,096            1.9           0.4
rollbacks only - consistent read              4,285            0.4           0.1
rows fetched via callback                10,779,322          995.8         227.3
session connect time             ################## ############## #############
session cursor cache hits                 3,770,537          348.3          79.5
session logical reads                    90,019,053        8,316.3       1,898.1
session uga memory                      857,321,984       79,202.2      18,077.1
session uga memory max                7,078,309,872      653,917.1     149,249.6
shared hash latch upgrades - no           8,178,727          755.6         172.5
sorts (disk)                                      0            0.0           0.0
sorts (memory)                              347,165           32.1           7.3
sorts (rows)                              9,745,946          900.4         205.5
summed dirty queue length                   399,925           37.0           8.4
switch current to new buffer                 15,066            1.4           0.3
table fetch by rowid                     54,156,582        5,003.2       1,141.9
table fetch continued row                    42,937            4.0           0.9
table scan blocks gotten                 17,321,177        1,600.2         365.2
table scan rows gotten                1,266,950,600      117,045.0      26,714.3
table scans (cache partitions)                    0            0.0           0.0
Instance Activity Stats  DB/Inst: PROD/prod  Snaps: 29861-29864

Statistic                                     Total     per Second     per Trans
-------------------------------- ------------------ -------------- -------------
table scans (direct read)                         0            0.0           0.0
table scans (long tables)                        13            0.0           0.0
table scans (rowid ranges)                        0            0.0           0.0
table scans (short tables)                  220,334           20.4           4.7
transaction rollbacks                           142            0.0           0.0
transaction tables consistent re                  1            0.0           0.0
transaction tables consistent re                218            0.0           0.0
undo change vector size                 438,430,192       40,503.6       9,244.5
user I/O wait time                          769,559           71.1          16.2
user calls                                9,922,245          916.7         209.2
user commits                                 41,492            3.8           0.9
user rollbacks                                5,934            0.6           0.1
workarea executions - onepass                     0            0.0           0.0
workarea executions - optimal               319,301           29.5           6.7
write clones created in backgrou                  0            0.0           0.0
write clones created in foregrou                 17            0.0           0.0
          -------------------------------------------------------------

Instance Activity Stats - Absolute Values  DB/Inst: PROD/prod  Snaps: 29861-298
-> Statistics with absolute values (should not be diffed)
-> Statistics identified by '(derived)' come from sources other than SYSSTAT

Statistic                            Begin Value       End Value
-------------------------------- --------------- ---------------
logons current                            13,106          13,113
open threads (derived)                         1               1
opened cursors current                     2,010           2,082
session cursor cache count                 1,593           1,884
workarea memory allocated                 17,146           4,729
          -------------------------------------------------------------

Instance Activity Stats - Thread Activity  DB/Inst: PROD/prod  Snaps: 29861-2986

Statistic                                     Total  per Hour
-------------------------------- ------------------ ---------
log switches (derived)                            2       .67
          -------------------------------------------------------------
Au début du rapport,
DB Time = 248.37 mn , soit 14902 s

Ca correspond à la valeur de la section TSM:
DB Time = 14902.42 s

Notons au passage que la section Timed Events semble utiliser les mêmes statistiques. Le wait event "CPU Time", par exemple, a la même valeur que dans la section TSM du rapport: 6134 s.

Par contre, si on prend les stats de la section IAS, on obtient des valeurs bien différentes:
DB Time= 4 795 658 cs = 47956.58 s ???
CPU used by this session = 632 116 cs = 6321.16 s (ok celle-ci n'est pas loin de 6134 s, mais quand même...)

J'ai trouvé un sujet similaire ici:

http://forums.oracle.com/forums/thre...90871&tstart=0

avec cette réponse:

Time Model statistics have a granularity of 1 microsecond.

Sysstat statistics, being from earlier versions, have a granularity of 1 centisecond.

Obviously, some readings would get "truncated" in the latter case.
Ca explique effectivement la différence entre "CPU Time" et "CPU used by this session", mais comment expliquer l'écart entre les "DB Time" ?

Je précise, aucune idée si ça a son importance dans le calcul, que le serveur hôte a 4 processeurs.