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POJVM Internals - Why does the same piece of code runs in different timings?
 

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  1. POJVM Internals - Why does the same piece of code runs in different timings?
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    <p>I am trying to understand the JVM options and came across the option <code>CompileThreshold</code>. I am running the below program:</p> <pre><code>public class Main { public static void main (String [] args) { for (int repeat = 0; repeat &lt; 200; ++ repeat) { long start = System.nanoTime(); sum (100); long end = System.nanoTime(); long diff = end - start; System.out.println (repeat + ": " + diff); } } ` public static int sum (int n) { if (n &lt;= 1) return 1; else return n + sum (n - 1); } } </code></pre> <p>I get the below output:</p> <pre><code>0: 8555 1: 6416 2: 6416 3: 5988 4: 6416 5: 8555 6: 5989 7: 6416 8: 6416 9: 5988 10: 5561 11: 5988 12: 5988 13: 5988 14: 5988 15: 5988 16: 5988 17: 5988 18: 5988 19: 6416 20: 5988 21: 5988 22: 5988 23: 5988 24: 5560 25: 6416 26: 5988 27: 5561 28: 5560 29: 5989 30: 5989 31: 5988 32: 21814 33: 6416 34: 6843 35: 6416 36: 6844 37: 6416 38: 6416 39: 6844 40: 6416 41: 6415 42: 6416 43: 5988 44: 6416 45: 6844 46: 6416 47: 6416 48: 6416 49: 6416 50: 6416 51: 6416 52: 5988 53: 6416 54: 6844 55: 6843 56: 6416 57: 6844 58: 6416 59: 6416 60: 6415 61: 6416 62: 6416 63: 6416 64: 5988 65: 5988 66: 6416 67: 6416 68: 6844 69: 6416 70: 6416 71: 6416 72: 6416 73: 6416 74: 6415 75: 6416 76: 6416 77: 6416 78: 6416 79: 6415 80: 6844 81: 5988 82: 6415 83: 6416 84: 6416 85: 6416 86: 6416 87: 6416 88: 7272 89: 6416 90: 6416 91: 6844 92: 6844 93: 6415 94: 6416 95: 6415 96: 6415 97: 6416 98: 6416 99: 25236 100: 6416 101: 6416 102: 6843 103: 6416 104: 5988 105: 6416 106: 6415 107: 6416 108: 6416 109: 6416 110: 6416 111: 6416 112: 6416 113: 6844 114: 6416 115: 6416 116: 6416 117: 5988 118: 6416 119: 6416 120: 6416 121: 6415 122: 6416 123: 6415 124: 6416 125: 6416 126: 6416 127: 6416 128: 5988 129: 5988 130: 6416 131: 6416 132: 5988 133: 5988 134: 6416 135: 6416 136: 5989 137: 6416 138: 6416 139: 5988 140: 5988 141: 6416 142: 5560 143: 5988 144: 6416 145: 6843 146: 6415 147: 6416 148: 6843 149: 11549 150: 6416 151: 6844 152: 6416 153: 6415 154: 6416 155: 5988 156: 5988 157: 6416 158: 6416 159: 6416 160: 6416 161: 6415 162: 6416 163: 6416 164: 6416 165: 6416 166: 5988 167: 5988 168: 5988 169: 6416 170: 6416 171: 6416 172: 5988 173: 5988 174: 6844 175: 5988 176: 6416 177: 6416 178: 6844 179: 6416 180: 6415 181: 6416 182: 5988 183: 5989 184: 6416 185: 6416 186: 6416 187: 6416 188: 5989 189: 5560 190: 5988 191: 6416 192: 6415 193: 6416 194: 18820 195: 1711 196: 1284 197: 2139 198: 1711 199: 1711 </code></pre> <p>If you observe, there are spikes in the times at 32, 99, 149, 194.<BR></p> <p>After 194, the time taken to run is comparitively less. Please explain this behaviour. Thanks.</p>
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