上一篇，我们借助Sqlite分析了2000w条数据，分析结果不错，但有一个问题：造数据很耗时（花费了2个小时）、sql查询同样很耗时（分组汇总查询一次大概需要30秒）。
那么，我们可以尝试下直接在内存中分析，那么会不会更快一些呢？
上代码：
1package com.lnwazg.a; 2 3import java.util.HashMap; 4import java.util.Map; 5 6import org.apache.commons.lang3.RandomUtils; 7 8import com.lnwazg.kit.describe.DescribeUtils; 9 10public class Test 11{ 12 public static void main(String[] args) 13 { 14 long begin = System.currentTimeMillis(); 15 System.out.println("begin..."); 16 //构造2000w条数据 17 int[] data = new int[20000000]; 18 for (int i = 0; i < data.length; i++) 19 { 20 data[i] = RandomUtils.nextInt(0, 1000); 21 } 22 System.out.println("OK"); 23 24 //统计每个随机数的出现次数 25 Map<Integer, Integer> numMap = new HashMap<>(); 26 for (int i = 0; i < data.length; i++) 27 { 28 if (!numMap.containsKey(data[i])) 29 { 30 numMap.put(data[i], 0); 31 } 32 numMap.put(data[i], numMap.get(data[i]) + 1); 33 } 34 35 long end = System.currentTimeMillis(); 36 System.out.println("Cost " + (end - begin) + " millseconds"); 37 //打印结果 38 DescribeUtils.describeMap(numMap); 39 } 40 41}
结果是：
1begin... 2OK 3Cost 819 millseconds 4key:0 value:20039 5key:1 value:20375 6key:2 value:20048 7key:3 value:19975 8key:4 value:20132 9key:5 value:19932 10key:6 value:19964 11key:7 value:19919 12key:8 value:19974 13key:9 value:20067 14key:10 value:19889 15key:11 value:19912 16key:12 value:20047 17key:13 value:19891 18key:14 value:20000 19key:15 value:19896 20key:16 value:20011 21key:17 value:19838 22key:18 value:19971 23key:19 value:19802 24key:20 value:19934 25key:21 value:20113 26key:22 value:20015 27key:23 value:20069 28key:24 value:19960 29key:25 value:20066 30key:26 value:19835 31key:27 value:20011 32key:28 value:20022 33key:29 value:20176 34key:30 value:20083 35key:31 value:19962 36key:32 value:19981 37key:33 value:19954 38key:34 value:19918 39key:35 value:20013 40key:36 value:19889 41key:37 value:19942 42key:38 value:20043 43key:39 value:20258 44key:40 value:19986 45key:41 value:19999 46key:42 value:19896 47key:43 value:20058 48key:44 value:19892 49key:45 value:20049 50key:46 value:20021 51key:47 value:20241 52key:48 value:20099 53key:49 value:19935 54key:50 value:19857 55key:51 value:19952 56key:52 value:20126 57key:53 value:19913 58key:54 value:20002 59key:55 value:20163 60key:56 value:20041 61key:57 value:20170 62key:58 value:20142 63key:59 value:20001 64key:60 value:20004 65key:61 value:20002 66key:62 value:20015 67key:63 value:20070 68key:64 value:20213 69key:65 value:20057 70key:66 value:19993 71key:67 value:19978 72key:68 value:19901 73key:69 value:19916 74key:70 value:20367 75key:71 value:20225 76key:72 value:19949 77key:73 value:20058 78key:74 value:20151 79key:75 value:19630 80key:76 value:19916 81key:77 value:19941 82key:78 value:20147 83key:79 value:20172 84key:80 value:20063 85key:81 value:20033 86key:82 value:20199 87key:83 value:19686 88key:84 value:19985 89key:85 value:20014 90key:86 value:20119 91key:87 value:20121 92key:88 value:19944 93key:89 value:19918 94key:90 value:20061 95key:91 value:20048 96key:92 value:20079 97key:93 value:20125 98key:94 value:20254 99key:95 value:19979 100key:96 value:20003 101key:97 value:20152 102key:98 value:20083 103key:99 value:20092 104key:100 value:20039 105key:101 value:19810 106key:102 value:20057 107key:103 value:20064 108key:104 value:20263 109key:105 value:20081 110key:106 value:19828 111key:107 value:20030 112key:108 value:20056 113key:109 value:19998 114key:110 value:20008 115key:111 value:19757 116key:112 value:20008 117key:113 value:20133 118key:114 value:19837 119key:115 value:20037 120key:116 value:19661 121key:117 value:19966 122key:118 value:20134 123key:119 value:19829 124key:120 value:19769 125key:121 value:20154 126key:122 value:19907 127key:123 value:20219 128key:124 value:20047 129key:125 value:20026 130key:126 value:19904 131key:127 value:19975 132key:128 value:19944 133key:129 value:19873 134key:130 value:20039 135key:131 value:19789 136key:132 value:19979 137key:133 value:19985 138key:134 value:19861 139key:135 value:20347 140key:136 value:19913 141key:137 value:19988 142key:138 value:20179 143key:139 value:20044 144key:140 value:19736 145key:141 value:19828 146key:142 value:19788 147key:143 value:19780 148key:144 value:20057 149key:145 value:19950 150key:146 value:19997 151key:147 value:19910 152key:148 value:20318 153key:149 value:20119 154key:150 value:20018 155key:151 value:20305 156key:152 value:19871 157key:153 value:20019 158key:154 value:19879 159key:155 value:20011 160key:156 value:19952 161key:157 value:19956 162key:158 value:20007 163key:159 value:19847 164key:160 value:20047 165key:161 value:20135 166key:162 value:19892 167key:163 value:20119 168key:164 value:20042 169key:165 value:20045 170key:166 value:19996 171key:167 value:19903 172key:168 value:20086 173key:169 value:19884 174key:170 value:19943 175key:171 value:20175 176key:172 value:20165 177key:173 value:19930 178key:174 value:19957 179key:175 value:19927 180key:176 value:19965 181key:177 value:19590 182key:178 value:20159 183key:179 value:19980 184key:180 value:20148 185key:181 value:19798 186key:182 value:20147 187key:183 value:19992 188key:184 value:19957 189key:185 value:20078 190key:186 value:20008 191key:187 value:20098 192key:188 value:20339 193key:189 value:19856 194key:190 value:19823 195key:191 value:20294 196key:192 value:20189 197key:193 value:20171 198key:194 value:20181 199key:195 value:20051 200key:196 value:19985 201key:197 value:20157 202key:198 value:19888 203key:199 value:19969 204key:200 value:19874 205key:201 value:19974 206key:202 value:20053 207key:203 value:20303 208key:204 value:20088 209key:205 value:20147 210key:206 value:19860 211key:207 value:20099 212key:208 value:19991 213key:209 value:19885 214key:210 value:19899 215key:211 value:20347 216key:212 value:19888 217key:213 value:20203 218key:214 value:20166 219key:215 value:19937 220key:216 value:19921 221key:217 value:20035 222key:218 value:20021 223key:219 value:20131 224key:220 value:20225 225key:221 value:20075 226key:222 value:19983 227key:223 value:19947 228key:224 value:19802 229key:225 value:20070 230key:226 value:19985 231key:227 value:19952 232key:228 value:19931 233key:229 value:20017 234key:230 value:20167 235key:231 value:20053 236key:232 value:20000 237key:233 value:20075 238key:234 value:19937 239key:235 value:20142 240key:236 value:19737 241key:237 value:19900 242key:238 value:20175 243key:239 value:19916 244key:240 value:20159 245key:241 value:20303 246key:242 value:19641 247key:243 value:20033 248key:244 value:19835 249key:245 value:19902 250key:246 value:20028 251key:247 value:19871 252key:248 value:20031 253key:249 value:19839 254key:250 value:19810 255key:251 value:20141 256key:252 value:19922 257key:253 value:19903 258key:254 value:20277 259key:255 value:20167 260key:256 value:20099 261key:257 value:20167 262key:258 value:19902 263key:259 value:20269 264key:260 value:20056 265key:261 value:20396 266key:262 value:19786 267key:263 value:20015 268key:264 value:19914 269key:265 value:20038 270key:266 value:19709 271key:267 value:20070 272key:268 value:20063 273key:269 value:19979 274key:270 value:19467 275key:271 value:19841 276key:272 value:20010 277key:273 value:19741 278key:274 value:20113 279key:275 value:19928 280key:276 value:19889 281key:277 value:19986 282key:278 value:20011 283key:279 value:20022 284key:280 value:20143 285key:281 value:20154 286key:282 value:19998 287key:283 value:20090 288key:284 value:19935 289key:285 value:20267 290key:286 value:19585 291key:287 value:20143 292key:288 value:19790 293key:289 value:19818 294key:290 value:19982 295key:291 value:20014 296key:292 value:20191 297key:293 value:19800 298key:294 value:19839 299key:295 value:20077 300key:296 value:19961 301key:297 value:19763 302key:298 value:19862 303key:299 value:19643 304key:300 value:19899 305key:301 value:20108 306key:302 value:20114 307key:303 value:20119 308key:304 value:19890 309key:305 value:20007 310key:306 value:19986 311key:307 value:19861 312key:308 value:20244 313key:309 value:19835 314key:310 value:19900 315key:311 value:19847 316key:312 value:20085 317key:313 value:19872 318key:314 value:19840 319key:315 value:20044 320key:316 value:19848 321key:317 value:19909 322key:318 value:19688 323key:319 value:19824 324key:320 value:19903 325key:321 value:20026 326key:322 value:20192 327key:323 value:20023 328key:324 value:20049 329key:325 value:19958 330key:326 value:20061 331key:327 value:20009 332key:328 value:20051 333key:329 value:20063 334key:330 value:20122 335key:331 value:19901 336key:332 value:19844 337key:333 value:20074 338key:334 value:19987 339key:335 value:20178 340key:336 value:20036 341key:337 value:20088 342key:338 value:20137 343key:339 value:20014 344key:340 value:19900 345key:341 value:20147 346key:342 value:19950 347key:343 value:19873 348key:344 value:20064 349key:345 value:20136 350key:346 value:20171 351key:347 value:19935 352key:348 value:19955 353key:349 value:20078 354key:350 value:19862 355key:351 value:20072 356key:352 value:19946 357key:353 value:20013 358key:354 value:19912 359key:355 value:20051 360key:356 value:19734 361key:357 value:20121 362key:358 value:20062 363key:359 value:19994 364key:360 value:19934 365key:361 value:19824 366key:362 value:20164 367key:363 value:19855 368key:364 value:20113 369key:365 value:20049 370key:366 value:19971 371key:367 value:19938 372key:368 value:19909 373key:369 value:19784 374key:370 value:20167 375key:371 value:19724 376key:372 value:19945 377key:373 value:20003 378key:374 value:19789 379key:375 value:19832 380key:376 value:19796 381key:377 value:20277 382key:378 value:19945 383key:379 value:20202 384key:380 value:20050 385key:381 value:20066 386key:382 value:19979 387key:383 value:19937 388key:384 value:19936 389key:385 value:20171 390key:386 value:19969 391key:387 value:19806 392key:388 value:19964 393key:389 value:20143 394key:390 value:19947 395key:391 value:20204 396key:392 value:20131 397key:393 value:20164 398key:394 value:20009 399key:395 value:20142 400key:396 value:20257 401key:397 value:19899 402key:398 value:19996 403key:399 value:20025 404key:400 value:19861 405key:401 value:19937 406key:402 value:19932 407key:403 value:19873 408key:404 value:20147 409key:405 value:20190 410key:406 value:20264 411key:407 value:20155 412key:408 value:20043 413key:409 value:19866 414key:410 value:20036 415key:411 value:19799 416key:412 value:20112 417key:413 value:20179 418key:414 value:20015 419key:415 value:20215 420key:416 value:20274 421key:417 value:19910 422key:418 value:20063 423key:419 value:19936 424key:420 value:19889 425key:421 value:19974 426key:422 value:19995 427key:423 value:19925 428key:424 value:20058 429key:425 value:20108 430key:426 value:20052 431key:427 value:19836 432key:428 value:20009 433key:429 value:20009 434key:430 value:19910 435key:431 value:20114 436key:432 value:19978 437key:433 value:19869 438key:434 value:19914 439key:435 value:19948 440key:436 value:19847 441key:437 value:20058 442key:438 value:19958 443key:439 value:20297 444key:440 value:20017 445key:441 value:20040 446key:442 value:20013 447key:443 value:19969 448key:444 value:19973 449key:445 value:19964 450key:446 value:20051 451key:447 value:19933 452key:448 value:19922 453key:449 value:20112 454key:450 value:19860 455key:451 value:20235 456key:452 value:20320 457key:453 value:19833 458key:454 value:19850 459key:455 value:20148 460key:456 value:19982 461key:457 value:19905 462key:458 value:20163 463key:459 value:19788 464key:460 value:20120 465key:461 value:20045 466key:462 value:20051 467key:463 value:20078 468key:464 value:20074 469key:465 value:20179 470key:466 value:19887 471key:467 value:19988 472key:468 value:19957 473key:469 value:19999 474key:470 value:20011 475key:471 value:20043 476key:472 value:20275 477key:473 value:19944 478key:474 value:20074 479key:475 value:19758 480key:476 value:20185 481key:477 value:20081 482key:478 value:20008 483key:479 value:19647 484key:480 value:20315 485key:481 value:20029 486key:482 value:20070 487key:483 value:19990 488key:484 value:19918 489key:485 value:20011 490key:486 value:20085 491key:487 value:19759 492key:488 value:20025 493key:489 value:20204 494key:490 value:19899 495key:491 value:20050 496key:492 value:19746 497key:493 value:19614 498key:494 value:19935 499key:495 value:20002 500key:496 value:19931 501key:497 value:20269 502key:498 value:19990 503key:499 value:20057 504key:500 value:19991 505key:501 value:20201 506key:502 value:19948 507key:503 value:19997 508key:504 value:20015 509key:505 value:19990 510key:506 value:19869 511key:507 value:19897 512key:508 value:20324 513key:509 value:20162 514key:510 value:19808 515key:511 value:20019 516key:512 value:19809 517key:513 value:20004 518key:514 value:20138 519key:515 value:19717 520key:516 value:20166 521key:517 value:20055 522key:518 value:20013 523key:519 value:20021 524key:520 value:19793 525key:521 value:19800 526key:522 value:19973 527key:523 value:19954 528key:524 value:19919 529key:525 value:19990 530key:526 value:19921 531key:527 value:20011 532key:528 value:19962 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value:19886 577key:573 value:19922 578key:574 value:19855 579key:575 value:19833 580key:576 value:19991 581key:577 value:20187 582key:578 value:20027 583key:579 value:20056 584key:580 value:19990 585key:581 value:20332 586key:582 value:20000 587key:583 value:19696 588key:584 value:19881 589key:585 value:19925 590key:586 value:19948 591key:587 value:20095 592key:588 value:20096 593key:589 value:19780 594key:590 value:19957 595key:591 value:19964 596key:592 value:20141 597key:593 value:19876 598key:594 value:20024 599key:595 value:20003 600key:596 value:20192 601key:597 value:20138 602key:598 value:19967 603key:599 value:20112 604key:600 value:19889 605key:601 value:19968 606key:602 value:20083 607key:603 value:19979 608key:604 value:19850 609key:605 value:20251 610key:606 value:19928 611key:607 value:19907 612key:608 value:19751 613key:609 value:19690 614key:610 value:20004 615key:611 value:20184 616key:612 value:20214 617key:613 value:19817 618key:614 value:20176 619key:615 value:20090 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value:20031 664key:660 value:20030 665key:661 value:20236 666key:662 value:20110 667key:663 value:20112 668key:664 value:20039 669key:665 value:19791 670key:666 value:19945 671key:667 value:20085 672key:668 value:19971 673key:669 value:19856 674key:670 value:20060 675key:671 value:20304 676key:672 value:19969 677key:673 value:19680 678key:674 value:20185 679key:675 value:20030 680key:676 value:20184 681key:677 value:19935 682key:678 value:19879 683key:679 value:20057 684key:680 value:20155 685key:681 value:20107 686key:682 value:19833 687key:683 value:20139 688key:684 value:20254 689key:685 value:20122 690key:686 value:20142 691key:687 value:20231 692key:688 value:20110 693key:689 value:20094 694key:690 value:19778 695key:691 value:20143 696key:692 value:19854 697key:693 value:19907 698key:694 value:19898 699key:695 value:19893 700key:696 value:19993 701key:697 value:20080 702key:698 value:20114 703key:699 value:20063 704key:700 value:20045 705key:701 value:19874 706key:702 value:19957 707key:703 value:19834 708key:704 value:20035 709key:705 value:19904 710key:706 value:20217 711key:707 value:19913 712key:708 value:19744 713key:709 value:20038 714key:710 value:20022 715key:711 value:20141 716key:712 value:19845 717key:713 value:19994 718key:714 value:19900 719key:715 value:20244 720key:716 value:19785 721key:717 value:20241 722key:718 value:19921 723key:719 value:19949 724key:720 value:19714 725key:721 value:19773 726key:722 value:19994 727key:723 value:20020 728key:724 value:19913 729key:725 value:20036 730key:726 value:19977 731key:727 value:20006 732key:728 value:20190 733key:729 value:19828 734key:730 value:20107 735key:731 value:19977 736key:732 value:19801 737key:733 value:19937 738key:734 value:20029 739key:735 value:19942 740key:736 value:19893 741key:737 value:19989 742key:738 value:19903 743key:739 value:20062 744key:740 value:19886 745key:741 value:20189 746key:742 value:20006 747key:743 value:20090 748key:744 value:20014 749key:745 value:19983 750key:746 value:19906 751key:747 value:19838 752key:748 value:20029 753key:749 value:19923 754key:750 value:20028 755key:751 value:19838 756key:752 value:19870 757key:753 value:19907 758key:754 value:19972 759key:755 value:19989 760key:756 value:20068 761key:757 value:20033 762key:758 value:20110 763key:759 value:19737 764key:760 value:20056 765key:761 value:19843 766key:762 value:19949 767key:763 value:19917 768key:764 value:19808 769key:765 value:20162 770key:766 value:19942 771key:767 value:19953 772key:768 value:19893 773key:769 value:19850 774key:770 value:20188 775key:771 value:19999 776key:772 value:20288 777key:773 value:20017 778key:774 value:19948 779key:775 value:19806 780key:776 value:19960 781key:777 value:19893 782key:778 value:19789 783key:779 value:19921 784key:780 value:20013 785key:781 value:20064 786key:782 value:20074 787key:783 value:19779 788key:784 value:19931 789key:785 value:20013 790key:786 value:19978 791key:787 value:19893 792key:788 value:20000 793key:789 value:19944 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结论：
内存计算因为少了网络传输、数据库操作、sql查询等时间的消耗，纯内存计算的效率惊人的高。
从构造数据，到分类汇总，仅消耗819毫秒时间！相比前篇的做法接近2小时的时间，快了将近10000倍有余！
内存计算胜在其算法可以高度定制优化，缺点则是通用性比较差。
传统的关系数据库的方式虽然查询速度较慢，但是数据可以持久化保存，并且除了统计次数之外还可以做很多其他的事情！
但是总体来说，内存计算的效率之高，着实给我留下了深刻的印象。由此，我对Spark在大数据分析领域的表现充满了期待！