This time I am not changing LWLock semantics :) Consider the a hash table partitioned in two different ways.
1. having S partitions, guarded by LWLocks on the same cache line. 2. having a single LWLock. Which one will give better concurrency? Which one will cost more to lock/unlock? I argue that having S partitions is better in several different ways. a. Concurrency of LW_EXCLUSIVE b. Reduced contention on LWLockWaitListLock c. Reduced CAS iterations in LWLockAtttemptLock d. Reduced waits (that implies wait list access and sleeping) I included a (pointless) benchmark result. And you can find a longer discussion in 0002 patch.
Statistics for 20 samples per process, from 1 to 12 processes,
of execution time of
```C
for(int i = 0; i < 100; ++i)
{
int idx = (int) pg_prng_int64_range(&rng, 0, n_part
- 1);
LWLock *lock = locks[idx];
sink += LWLockAcquire(lock, LW_SHARED) ? 1 : 0;
LWLockRelease(lock);
}
```
n_proc | op | avg | med | std | min | max
--------+----+-------+-------+------+-------+-------
1 | 1 | 16.17 | 15.83 | 1.56 | 15.41 | 22.50
1 | 2 | 15.06 | 15.00 | 0.24 | 14.58 | 15.42
1 | 3 | 14.48 | 14.58 | 0.43 | 13.75 | 15.42
1 | 4 | 13.96 | 13.96 | 0.21 | 13.75 | 14.17
1 | 5 | 15.60 | 15.83 | 0.70 | 14.17 | 16.67
1 | 6 | 13.85 | 13.75 | 0.30 | 13.33 | 14.58
1 | 7 | 13.27 | 13.33 | 0.25 | 12.91 | 13.75
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+-------+-------+--------
2 | 1 | 110.95 | 112.29 | 10.26 | 91.25 | 122.08
2 | 2 | 114.23 | 119.79 | 12.25 | 89.17 | 126.66
2 | 3 | 105.54 | 108.34 | 9.45 | 89.17 | 117.09
2 | 4 | 103.17 | 106.04 | 10.06 | 84.59 | 116.67
2 | 5 | 83.83 | 86.67 | 10.88 | 56.25 | 95.83
2 | 6 | 74.69 | 78.96 | 7.97 | 59.17 | 84.58
2 | 7 | 70.84 | 72.50 | 7.47 | 53.33 | 84.17
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+-------+--------+--------
3 | 1 | 202.20 | 208.96 | 21.93 | 113.34 | 234.16
3 | 2 | 197.93 | 198.75 | 19.66 | 159.58 | 281.67
3 | 3 | 180.74 | 180.63 | 12.75 | 152.09 | 249.16
3 | 4 | 171.51 | 173.54 | 14.39 | 138.33 | 240.00
3 | 5 | 145.51 | 146.88 | 7.94 | 121.25 | 167.92
3 | 6 | 133.81 | 131.67 | 15.64 | 115.42 | 205.83
3 | 7 | 124.40 | 123.55 | 9.83 | 111.66 | 187.92
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+--------+--------+---------
4 | 1 | 328.77 | 301.25 | 262.05 | 166.66 | 2382.92
4 | 2 | 272.43 | 278.13 | 177.51 | 25.42 | 1661.25
4 | 3 | 270.32 | 268.13 | 314.53 | 18.33 | 2998.75
4 | 4 | 235.94 | 252.09 | 59.59 | 129.59 | 535.83
4 | 5 | 227.15 | 245.21 | 39.19 | 127.92 | 277.08
4 | 6 | 206.78 | 220.21 | 35.21 | 132.08 | 261.25
4 | 7 | 189.20 | 207.71 | 42.22 | 25.42 | 238.75
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+---------+--------+----------
5 | 1 | 505.15 | 521.46 | 104.74 | 181.67 | 956.66
5 | 2 | 448.70 | 455.42 | 83.08 | 292.09 | 1157.08
5 | 3 | 425.05 | 432.92 | 33.22 | 338.75 | 470.84
5 | 4 | 454.80 | 395.00 | 729.49 | 190.42 | 7654.58
5 | 5 | 581.73 | 344.17 | 2371.56 | 30.83 | 24020.00
5 | 6 | 318.73 | 319.38 | 27.74 | 251.25 | 363.34
5 | 7 | 304.48 | 307.29 | 29.92 | 242.50 | 404.17
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+--------+--------+---------
6 | 1 | 629.19 | 618.55 | 97.59 | 312.91 | 760.42
6 | 2 | 573.93 | 567.09 | 115.77 | 299.16 | 1374.16
6 | 3 | 515.10 | 535.00 | 77.25 | 175.00 | 625.84
6 | 4 | 482.97 | 498.54 | 89.71 | 23.34 | 922.92
6 | 5 | 454.85 | 482.92 | 69.80 | 268.33 | 804.58
6 | 6 | 430.80 | 430.21 | 185.31 | 262.09 | 2369.17
6 | 7 | 391.96 | 412.92 | 55.61 | 233.75 | 450.42
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+--------+--------+---------
7 | 1 | 818.72 | 801.67 | 647.36 | 23.75 | 7978.33
7 | 2 | 689.89 | 720.21 | 128.47 | 15.00 | 835.42
7 | 3 | 651.53 | 676.04 | 72.80 | 335.84 | 725.42
7 | 4 | 649.07 | 621.67 | 681.96 | 210.00 | 8581.25
7 | 5 | 545.21 | 535.42 | 191.00 | 29.58 | 2657.50
7 | 6 | 496.41 | 495.00 | 52.38 | 373.33 | 667.50
7 | 7 | 472.23 | 477.71 | 49.74 | 320.42 | 550.00
n_proc | op | avg | med | std | min | max
--------+----+--------+--------+---------+-------+----------
8 | 1 | 808.78 | 897.29 | 245.17 | 12.08 | 1079.58
8 | 2 | 804.72 | 911.04 | 263.41 | 13.75 | 1455.41
8 | 3 | 725.86 | 789.79 | 209.63 | 14.58 | 1249.17
8 | 4 | 711.27 | 759.58 | 259.57 | 14.16 | 3036.67
8 | 5 | 670.01 | 763.34 | 227.69 | 13.75 | 1385.00
8 | 6 | 916.34 | 679.38 | 3069.38 | 12.91 | 35931.66
8 | 7 | 527.36 | 638.96 | 197.90 | 12.91 | 706.67
n_proc | op | avg | med | std | min | max
--------+----+---------+--------+---------+-------+----------
9 | 1 | 765.00 | 891.04 | 663.25 | 11.25 | 8188.33
9 | 2 | 820.31 | 881.46 | 991.92 | 13.33 | 13385.42
9 | 3 | 820.82 | 819.17 | 1492.09 | 12.91 | 17189.17
9 | 4 | 1077.87 | 753.96 | 3235.68 | 13.34 | 32688.33
9 | 5 | 805.22 | 732.08 | 2961.26 | 13.75 | 40145.00
9 | 6 | 642.98 | 645.42 | 1366.95 | 12.50 | 18573.33
9 | 7 | 701.65 | 579.79 | 2014.68 | 12.09 | 21728.33
n_proc | op | avg | med | std | min | max
--------+----+---------+--------+---------+-------+----------
10 | 1 | 1059.40 | 926.88 | 4698.34 | 12.08 | 66922.91
10 | 2 | 1166.22 | 938.75 | 3651.48 | 12.91 | 47069.17
10 | 3 | 1756.45 | 831.04 | 8438.07 | 12.09 | 83536.66
10 | 4 | 929.20 | 778.76 | 4466.06 | 12.09 | 63622.08
10 | 5 | 623.25 | 782.51 | 309.65 | 14.16 | 848.75
10 | 6 | 651.93 | 674.79 | 1212.02 | 12.92 | 13497.08
10 | 7 | 528.45 | 651.67 | 253.60 | 12.50 | 713.33
--------+----+---------+--------+----------+-------+-----------
11 | 1 | 678.42 | 912.09 | 417.84 | 10.83 | 1184.58
11 | 2 | 1654.62 | 780.00 | 10701.60 | 12.91 | 119140.00
11 | 3 | 1403.58 | 799.58 | 8454.71 | 12.50 | 90955.00
11 | 4 | 1046.45 | 721.25 | 5752.25 | 12.92 | 80720.84
11 | 5 | 495.42 | 663.54 | 329.99 | 12.92 | 1041.25
11 | 6 | 537.54 | 641.25 | 1020.01 | 11.66 | 14979.16
11 | 7 | 410.60 | 475.62 | 271.27 | 12.08 | 701.67
--------+----+---------+--------+----------+-------+-----------
12 | 1 | 1985.79 | 838.12 | 12980.48 | 12.08 | 172370.00
12 | 2 | 1637.70 | 912.50 | 9014.67 | 12.92 | 100103.75
12 | 3 | 1815.80 | 821.25 | 11141.96 | 12.50 | 101198.75
12 | 4 | 1352.02 | 757.71 | 9253.80 | 12.50 | 113313.75
12 | 5 | 998.03 | 768.96 | 7319.46 | 12.50 | 113783.33
12 | 6 | 468.17 | 668.75 | 316.41 | 11.67 | 828.33
12 | 7 | 698.87 | 641.88 | 3133.12 | 12.09 | 46641.25
v1-0002-introduce-LWLockAligned.patch
Description: Binary data
v1-0001-LWLock-struct-layout.patch
Description: Binary data
