JIT mysteries

Question

hello
Source
public final void testSpeedComplexSelect() throws SQLException {
for (int i=0;i<5000;i++)
long t1=System.currentTimeMillis();
String sql = "select b.E,a.B " + "from TABLE1 a,TABLE2 b "
+ "where a.ID=6 or a.A='5625' and "
+ " a.B='olivier' and a.C=12345 and b.ID=1"
+ " and b.C='45' and b.D='65' and b.E=2";
SelectRequest select=new SelectRequest(sql,BlackBoxTest.SID,BlackBoxTest.login);
select.isInvolved();
if (Application.PROFILE) System.out.println("h-"+(System.currentTimeMillis()-Application.t1));
//select.getModifiedSQL();
long t2=System.currentTimeMillis();
long time=t2-t1;
System.out.println("Parsing a complex select takes="+time);
This code between the 2 System.currentTimeMillis is not supposed to take more than 5/10ms.
Execution on AIX (JVM IBM 1.4)
java -Xms1024m -Xmx2048m -verbose:gc -Xverbosegclog:./gc.txt -classpath ${CLASSPATH} junit.textui.TestRunner UnitTest.PerformanceTest
Parsing a complex select takes=12
Parsing a complex select takes=11
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=1
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=5
Parsing a complex select takes=1
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=1
Parsing a complex select takes=1
Parsing a complex select takes=3
Parsing a complex select takes=2
Parsing a complex select takes=3
Parsing a complex select takes=193
Parsing a complex select takes=203
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=2
Parsing a complex select takes=1
Code is getting faster because of JIT optimizations, isn't it ?
but why the hell the 18h and 19th run always takes 200 ms and after 0 ????
by the way is there a more precise way of taking time than System.currentTimeMillis() ?
I thought it was gc, but gc run never takes more than 2ms
Au niveau du gc
bash-3.00$ cat gc.txt
<GC[0]: Expanded System Heap by 65536 bytes
<GC[0]: Expanded System Heap by 65536 bytes
<GC[0]: Expanded System Heap by 65536 bytes
<AF[1]: Allocation Failure. need 4112 bytes, 0 ms since last AF>
<AF[1]: managing allocation failure, action=1 (1576/3983128) (209640/209640)>
<GC(1): GC cycle started Thu Aug 21 20:48:37 2008
<GC(1): freed 2696384 bytes, 69% free (2907600/4192768), in 2 ms>
<GC(1): mark: 1 ms, sweep: 1 ms, compact: 0 ms>
<GC(1): refs: soft 0 (age >= 32), weak 0, final 11, phantom 0>
<AF[1]: completed in 2 ms>
<AF[2]: Allocation Failure. need 528 bytes, 872 ms since last AF>
<AF[2]: managing allocation failure, action=1 (0/3983128) (209640/209640)>
<GC(2): GC cycle started Thu Aug 21 20:48:38 2008
<GC(2): freed 2612304 bytes, 67% free (2821944/4192768), in 2 ms>
<GC(2): mark: 2 ms, sweep: 0 ms, compact: 0 ms>
<GC(2): refs: soft 0 (age >= 32), weak 0, final 3, phantom 0>
<AF[2]: completed in 2 ms>
<AF[3]: Allocation Failure. need 528 bytes, 35 ms since last AF>
<AF[3]: managing allocation failure, action=1 (0/3983128) (209640/209640)>
<GC(3): GC cycle started Thu Aug 21 20:48:38 2008
<GC(3): freed 2622392 bytes, 67% free (2832032/4192768), in 2 ms>
<GC(3): mark: 2 ms, sweep: 0 ms, compact: 0 ms>
<GC(3): refs: soft 0 (age >= 32), weak 0, final 0, phantom 0>
<AF[3]: completed in 2 ms>
Any idea ??
Same code run on jvm SUN on windows is even more weird to me because it starts with 0 and periodically gives a 16ms
0Parsing a complex select takes=0
1Parsing a complex select takes=0
2Parsing a complex select takes=0
3Parsing a complex select takes=0
4Parsing a complex select takes=0
5Parsing a complex select takes=0
6Parsing a complex select takes=0
7Parsing a complex select takes=0
8Parsing a complex select takes=0
9Parsing a complex select takes=0
*10Parsing a complex select takes=16*
11Parsing a complex select takes=0
12Parsing a complex select takes=0
13Parsing a complex select takes=0
14Parsing a complex select takes=0
15Parsing a complex select takes=0
16Parsing a complex select takes=0
17Parsing a complex select takes=0
18Parsing a complex select takes=0
19Parsing a complex select takes=0
20Parsing a complex select takes=0
21Parsing a complex select takes=0
*22Parsing a complex select takes=15*
23Parsing a complex select takes=0
24Parsing a complex select takes=0
25Parsing a complex select takes=0
26Parsing a complex select takes=0
27Parsing a complex select takes=0
28Parsing a complex select takes=0
29Parsing a complex select takes=0
30Parsing a complex select takes=0
31Parsing a complex select takes=0
32Parsing a complex select takes=0
33Parsing a complex select takes=0
34Parsing a complex select takes=0
35Parsing a complex select takes=0
36Parsing a complex select takes=0
37Parsing a complex select takes=0
38Parsing a complex select takes=0
39Parsing a complex select takes=0
40Parsing a complex select takes=0
41Parsing a complex select takes=0
42Parsing a complex select takes=0
43Parsing a complex select takes=0
44Parsing a complex select takes=0
45Parsing a complex select takes=0
46Parsing a complex select takes=0
47Parsing a complex select takes=0
48Parsing a complex select takes=0
49Parsing a complex select takes=0
50Parsing a complex select takes=0
51Parsing a complex select takes=0
52Parsing a complex select takes=0
53Parsing a complex select takes=0
54Parsing a complex select takes=0
55Parsing a complex select takes=0
56Parsing a complex select takes=0
57Parsing a complex select takes=0
58Parsing a complex select takes=0
59Parsing a complex select takes=0
60Parsing a complex select takes=0
61Parsing a complex select takes=0
62Parsing a complex select takes=0
63Parsing a complex select takes=0
64Parsing a complex select takes=0
65Parsing a complex select takes=0
66Parsing a complex select takes=0
67Parsing a complex select takes=0
68Parsing a complex select takes=0
69Parsing a complex select takes=0
70Parsing a complex select takes=0
71Parsing a complex select takes=0
72Parsing a complex select takes=0
73Parsing a complex select takes=0
74Parsing a complex select takes=0
75Parsing a complex select takes=0
76Parsing a complex select takes=0
77Parsing a complex select takes=0
78Parsing a complex select takes=0
79Parsing a complex select takes=0
80Parsing a complex select takes=0
81Parsing a complex select takes=0
82Parsing a complex select takes=0
83Parsing a complex select takes=0
84Parsing a complex select takes=0
85Parsing a complex select takes=0
86Parsing a complex select takes=0
87Parsing a complex select takes=0
*88Parsing a complex select takes=15*
89Parsing a complex select takes=0
90Parsing a complex select takes=0
91Parsing a complex select takes=0
92Parsing a complex select takes=0
93Parsing a complex select takes=0
94Parsing a complex select takes=0
95Parsing a complex select takes=0
96Parsing a complex select takes=0
97Parsing a complex select takes=0
98Parsing a complex select takes=0
99Parsing a complex select takes=0
100Parsing a complex select takes=0
what is going on ?
can I put a hook on gc ? on JIT compilation ?
thanks !

Answer 1

following swmtgoet_x tip I tried that code but it produces very similar result.
I don't think there is a gc issue here.
          for (int i=0;i<5000;i++)
          long t1=System.currentTimeMillis();
          String sql = "select b.E,a.B " + "from TABLE1 a,TABLE2 b "
          + "where a.ID=6 or a.A='5625' and "
          + " a.B='olivier' and a.C=12345 and b.ID=1"
          + " and b.C='45' and b.D='65' and b.E=2";
          SelectRequest select=new SelectRequest(sql,BlackBoxTest.SID,BlackBoxTest.login);
          select.isInvolved();
          if (Application.PROFILE) System.out.println("h-"+(System.currentTimeMillis()-Application.t1));
          //select.getModifiedSQL();
          long t2=System.currentTimeMillis();
          long time=t2-t1;
          System.out.println("Parsing a complex select takes="+time);
          System.gc();
          Thread.sleep(1000);
Parsing a complex select takes=12
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=3
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=15
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=2
Parsing a complex select takes=1
Parsing a complex select takes=2
Parsing a complex select takes=3
Parsing a complex select takes=2
Parsing a complex select takes=3
Parsing a complex select takes=195
Parsing a complex select takes=203
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=1
Parsing a complex select takes=1
Parsing a complex select takes=1
Parsing a complex select takes=1
Parsing a complex select takes=0
Parsing a complex select takes=0
Parsing a complex select takes=0