在 ORACLE 数据库提供的性能监督，问题考察的工具中，AWR 也是一个十分重要的机能。
AWR 和 STATSPACK 相似，都是定时取对于 DB 整体情况的 Snapshot，而后取指定的两个 Snapshot 算出差值，从而失去两个工夫点之间的 DB 情况。
然而，AWR 和 STATSPACK 又存在以下区别：
1. AWR 是免费的；STATSPACK 是收费的。2. AWR 只能在 EE 应用；STATSPACK 能够在 SE 应用。3. AWR 是用 C 语言写的，采纳 DMA（direct memory access）形式间接拜访内存；STATSPACK 是用 Pl/SQL 写的，须要走和一般 SQL 文的一样的 Parse --> Execute --> Fetch 解决形式。4. AWR 的 SnapShot 的采集，治理，删除是主动的；STATSPACK 是须要用户本人写 Job 实现的。因为 AWR 外面蕴含的数据是十分丰盛的，所以应用办法也是多种多样的，明天只举一个小例子。
客户报告：3 月份开始，AWR Report 的“Buffer Hit %”大幅降落。提供材料：2 月份和 3 月份的 AWR Report。请求事项：起因确认
首先，须要确认一下“Buffer Hit %”的计算方法。
参考 Note：AWR レポートに出力されるバッファ・キャッシュ・ヒット率の値が正しくない (KROWN:142990) (ドキュメント ID 1750026.1)
1 - (('physical reads cache') / ('consistent gets from cache' + 'db block gets from cache')
而后，依据下面的计算式，在 AWR Report 外面蕴含的以下 3 个待机的统计值：
physical reads cache
consistent gets from cache
db block gets from cache
应用一点小伎俩，把蕴含在客户提供的 AWR Report 里的待机值取出来。
◆2 月份
physical reads cache consistent gets from cache db block gets from cache Buffer Hit% 计算值
awrrpt_Node2_11117_11118.html 1,367,229 123,185,553 2,943,455 98.92 98.92
awrrpt_Node2_11118_11119.html 654,533 127,234,595 450,102 99.49 99.49
awrrpt_Node2_11119_11120.html 1,003,773 130,975,087 567,126 99.24 99.24
awrrpt_Node2_11120_11121.html 1,057,474 129,739,916 510,676 99.19 99.19
awrrpt_Node2_11121_11122.html 806,442 139,078,160 551,815 99.42 99.42
awrrpt_Node2_11122_11123.html 235,276 136,269,822 10,762,534 99.84 99.84
awrrpt_Node2_11123_11124.html 1,314,543 125,717,238 611,062 98.96 98.96
awrrpt_Node2_11124_11125.html 206,319 116,914,725 434,141 99.82 99.82
awrrpt_Node2_11125_11126.html 1,777,179 128,968,423 16,465,897 98.78 98.78
awrrpt_Node2_11126_11127.html 326,310 132,073,666 424,109 99.75 99.75
awrrpt_Node2_11127_11128.html 1,474,847 120,674,422 545,747 98.78 98.78
awrrpt_Node2_11128_11129.html 213,332 118,891,545 386,444 99.82 99.82
awrrpt_Node2_11129_11130.html 1,185,440 129,554,468 849,653 99.09 99.09
awrrpt_Node2_11130_11131.html 291,913 123,851,398 442,434 99.77 99.77
awrrpt_Node2_11131_11132.html 1,277,884 121,854,109 504,381 98.96 98.96
awrrpt_Node2_11132_11133.html 258,371 135,959,454 447,235 99.81 99.81
awrrpt_Node2_11133_11134.html 1,209,367 122,064,000 532,350 99.01 99.01
awrrpt_Node2_11134_11135.html 189,544 119,130,960 401,270 99.84 99.84
awrrpt_Node2_11135_11136.html 1,277,111 143,900,150 626,518 99.12 99.12
awrrpt_Node2_11136_11137.html 233,943 131,330,750 745,066 99.82 99.82
awrrpt_Node2_11137_11138.html 1,146,509 133,473,223 484,318 99.14 99.14
awrrpt_Node2_11138_11139.html 163,751 115,964,992 318,123 99.86 99.86
awrrpt_Node2_11139_11140.html 1,183,224 128,098,854 909,259 99.08 99.08
awrrpt_Node2_11140_11141.html 228,650 121,668,141 16,226,344 99.83 99.83
awrrpt_Node2_11141_11142.html 1,243,272 133,804,917 366,931 99.07 99.07
awrrpt_Node2_11142_11143.html 189,297 140,340,156 324,678 99.87 99.87
awrrpt_Node2_11143_11144.html 1,106,725 108,323,111 393,184 98.98 98.98
awrrpt_Node2_11144_11145.html 217,717 117,828,642 361,044 99.82 99.82
awrrpt_Node2_11145_11146.html 1,121,367 109,813,017 443,225 98.98 98.98
awrrpt_Node2_11146_11147.html 365,329 121,099,235 9,842,513 99.72 99.72
awrrpt_Node2_11147_11148.html 177,362 127,510,344 69,653,323 99.91 99.91
awrrpt_Node2_11148_11149.html 122,136 105,458,188 289,046 99.88 99.88
awrrpt_Node2_11149_11150.html 97,822 97,544,757 247,641 99.9 99.9
awrrpt_Node2_11150_11151.html 60,263 88,334,090 202,901 99.93 99.93
awrrpt_Node2_11151_11152.html 55,919 77,791,297 177,600 99.93 99.93
awrrpt_Node2_11152_11153.html 28,153 69,924,517 191,956 99.96 99.96
awrrpt_Node2_11153_11154.html 33,529 70,628,356 1,235,751 99.95 99.95
awrrpt_Node2_11154_11155.html 15,681 63,324,755 122,490 99.98 99.98
awrrpt_Node2_11155_11156.html 20,723 55,369,179 127,362 99.96 99.96
awrrpt_Node2_11156_11157.html 20,181 60,451,827 107,454 99.97 99.97
awrrpt_Node2_11157_11158.html 290,997 63,362,994 1,256,035 99.55 99.55
awrrpt_Node2_11158_11159.html 3,134,999 59,561,257 65,422,469 97.49 97.49
awrrpt_Node2_11159_11160.html 12,603,133 671,968,974 12,634,978 98.16 98.16
awrrpt_Node2_11160_11161.html 7,986,463 72,291,100 78,403,181 94.7 94.7
awrrpt_Node2_11161_11162.html 165,156 77,928,307 199,674 99.79 99.79
awrrpt_Node2_11162_11163.html 143,307 84,143,818 246,087 99.83 99.83
awrrpt_Node2_11163_11164.html 138,990 94,506,704 272,167 99.85 99.85
awrrpt_Node2_11164_11165.html 137,758 99,008,540 295,274 99.86 99.86
◆3 月份
physical reads cache consistent gets from cache db block gets from cache Buffer Hit% 计算值
awrrpt_Node2_22213_22214.html 18,833,127 87,719,557 11,547,532 81.03 81.03
awrrpt_Node2_22214_22215.html 19,293,314 84,003,101 777,801 77.24 77.24
awrrpt_Node2_22215_22216.html 19,055,550 97,849,548 901,390 80.7 80.7
awrrpt_Node2_22216_22217.html 19,263,835 88,958,016 787,016 78.53 78.53
awrrpt_Node2_22217_22218.html 19,156,451 85,629,731 817,799 77.84 77.84
awrrpt_Node2_22218_22219.html 19,339,294 90,498,771 11,164,125 80.98 80.98
awrrpt_Node2_22219_22220.html 19,394,785 85,818,970 998,442 77.66 77.66
awrrpt_Node2_22220_22221.html 19,298,334 83,376,226 838,372 77.08 77.08
awrrpt_Node2_22221_22222.html 19,334,326 92,402,004 909,433 79.28 79.28
awrrpt_Node2_22222_22223.html 19,590,098 117,188,196 27,331,324 86.44 86.44
awrrpt_Node2_22223_22224.html 19,756,886 79,694,538 783,825 75.45 75.45
awrrpt_Node2_22224_22225.html 20,142,492 69,985,919 637,065 71.48 71.48
awrrpt_Node2_22225_22226.html 19,284,672 68,688,658 1,062,320 72.35 72.35
awrrpt_Node2_22226_22227.html 18,973,492 78,436,829 602,573 75.99 75.99
awrrpt_Node2_22227_22228.html 19,295,820 83,930,250 754,265 77.21 77.21
awrrpt_Node2_22228_22229.html 19,299,273 95,240,240 710,249 79.89 79.89
awrrpt_Node2_22229_22230.html 19,282,703 86,314,357 765,538 77.86 77.86
awrrpt_Node2_22230_22231.html 19,471,142 92,579,836 675,708 79.12 79.12
awrrpt_Node2_22231_22232.html 19,456,272 87,360,635 922,862 77.96 77.96
awrrpt_Node2_22232_22233.html 19,426,444 78,029,665 775,880 75.35 75.35
awrrpt_Node2_22233_22234.html 19,134,299 107,192,096 689,028 82.26 82.26
awrrpt_Node2_22234_22235.html 19,539,297 88,922,077 603,820 78.17 78.17
awrrpt_Node2_22235_22236.html 19,548,117 74,524,524 10,886,459 77.11 77.11
awrrpt_Node2_22236_22237.html 19,571,235 69,991,952 6,898,460 74.55 74.55
awrrpt_Node2_22237_22238.html 19,535,153 68,002,826 669,415 71.55 71.55
awrrpt_Node2_22238_22239.html 19,743,665 69,208,411 676,517 71.75 71.75
awrrpt_Node2_22239_22240.html 19,315,599 70,517,718 603,436 72.84 72.84
awrrpt_Node2_22240_22241.html 19,702,422 85,042,101 730,447 77.03 77.03
awrrpt_Node2_22241_22242.html 29,386,292 78,899,276 780,642 63.12 63.12
awrrpt_Node2_22242_22243.html 20,363,303 76,394,697 5,406,729 75.11 75.11
awrrpt_Node2_22243_22244.html 20,493,153 85,604,990 75,059,277 87.24 87.24
awrrpt_Node2_22244_22245.html 20,606,911 67,653,183 578,796 69.8 69.8
awrrpt_Node2_22245_22246.html 20,644,327 59,512,101 553,342 65.63 65.63
awrrpt_Node2_22246_22247.html 20,236,428 50,540,686 491,729 60.35 60.35
awrrpt_Node2_22247_22248.html 20,401,296 46,971,705 442,071 56.97 56.97
awrrpt_Node2_22248_22249.html 20,507,154 43,251,247 457,559 53.08 53.08
awrrpt_Node2_22249_22250.html 19,866,674 40,809,028 402,312 51.79 51.79
awrrpt_Node2_22250_22251.html 20,011,908 38,691,219 413,919 48.83 48.83
awrrpt_Node2_22251_22252.html 18,834,446 36,228,742 318,118 48.46 48.46
awrrpt_Node2_22252_22253.html 19,089,954 37,053,290 409,520 49.04 49.04
awrrpt_Node2_22253_22254.html 19,515,077 37,761,037 354,648 48.8 48.8
awrrpt_Node2_22254_22255.html 22,171,394 40,008,660 10,777,153 56.34 56.34
awrrpt_Node2_22255_22256.html 25,519,651 586,686,934 68,644,322 96.11 96.11
awrrpt_Node2_22256_22257.html 35,365,336 119,680,111 11,297,447 73 73
awrrpt_Node2_22257_22258.html 22,012,146 58,094,571 68,177,156 82.57 82.57
awrrpt_Node2_22258_22259.html 21,263,614 65,416,659 575,772 67.78 67.78
awrrpt_Node2_22259_22260.html 21,357,383 68,498,396 821,252 69.19 69.19
awrrpt_Node2_22260_22261.html 21,006,076 74,916,494 16,673,221 77.07 77.07
通过比拟 AWR Report 里获得的”Buffer Hit%“和计算出来的”Buffer Hit%“，咱们发现两个值是相等的，这就证实了咱们后面考察到的计算方法是正确的。
而后应用 Excel 做几个简略的曲线图：
◆Buffer Hit% 曲线图
◆physical reads cache 曲线图
◆consistent gets from cache 曲线图
◆db block gets from cache 曲线图
通过下面的曲线图，能够直观的看到以下两个特点：
1. Buffer Hit% 和 physical reads cache 的变化趋势相同。2. consistent gets from cache 和 db block gets from cache 的变化趋势雷同。再联合 Buffer Hit% 的计算式，就能够得出这个问题的起因是 3 月份的”physical reads cache“减少造成的论断了。
Buffer Hit% = 1 – ((‘physical reads cache’) / (‘consistent gets from cache’ + ‘db block gets from cache’)
那么，还有以下两个问题须要明确：
1. 那些解决（SQL 文）造成了物理读。2. 物理读的对象（Segment）是那些。这两个问题能够通过 AWR Report 里的”SQL ordered by Reads“和”Segments by Physical Reads“进行确认。
因为这部分数据蕴含客户信息，就不在这里展现了。
最初，再罗嗦一句，剖析 AWR Report 和 ASH 数据一样，都要无意识的先确定考察方向，不能胡子眉毛一把抓，没有重点。
当前有好的例子再和大家分享。
2021/03/26 @ Dalian