Btree Index storage internal

本文主要是介绍Btree Index storage internal，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

---------------- Btree Index 原理 ---------------- 1.Oracle中的Btree Index具有3大结构，root节点，branch节点，leaf节点.Root节点始终紧跟索引段头. 当索引比较小的时候，root节点，branch节点，leaf节点都存储在同一个block中.Branch节点主要存储了索引的键值,但是这个键值并不是完整的，它只是完整索引值的部分前缀.同时Branch节点还存储了指向 leaf节点的指针(DBA)，另外有个主意的是branch节点中还有个叫kdxbrlmc的指针.Leaf节点主要存储了完整的索引键值，以及相关索引键值的部分rowid(这个rowid去掉了data object number部分)，同时leaf 节点还存储了2个指针(DBA)，他们分别指向上一个leaf节点以及下一个leaf节点. 2.Btree Index 是始终平衡的，也就是说从Root节点到 Leaf 节点的任何一个路径都是等距离的. 3.Btree Index 默认是按照索引值升序排列的，当然了我们可以在创建/重建的时候设置它降序排列. 4.Index Scan 的时候，采用的是 sequential read,并且一次只能读一个block(INDEX FAST FULL SCAN 除外). 5.Btree Index Update的时候，先做的是 delete,然后进行insert. 6.Btree Index 不存储 Null值，但是如果组合索引其中一列是非Null的，那么组合索引也会存储Null值. --------------------------------- Btree Index 存储原理 --------------------------------- SQL> select * from v$version where rownum=1; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod SQL> show user User is "robinson" SQL> create table test as select * from dba_objects; Table created SQL> select count(*) from test; COUNT(*) ---------- 50352 SQL> insert into test select * from dba_objects; 50352 rows inserted SQL> commit; Commit complete SQL> select count(*) from test; COUNT(*) ---------- 100704 SQL> create index i_test_object_name on test(object_name); Index created ------------------------------------------------------------------------------ 我们现在来看一下索引的Blevel,什么是Blevel,Blevel可以通过DBA_INDEXES.Blevel获得 ------------------------------------------------------------------------------ B*-Tree level: depth of the index from its root block to its leaf blocks. A depth of 0 indicates that the root block and leaf block are the same. 从 root block 到 leaf block的深度. 如果root block 和 leaf block在同一个块中那么 Blevel=0 SQL> select index_name,blevel from dba_indexes where index_name='I_TEST_OBJECT_NAME'; INDEX_NAME BLEVEL ------------------------------ ---------- I_TEST_OBJECT_NAME 2 ----------------------------------------------------------------------------------- 我们现在来看一下索引的height，索引的高度等于Blevel+1，height可以通过INDEX_STATS获得 ----------------------------------------------------------------------------------- SQL> analyze index I_TEST_OBJECT_NAME validate structure; Index analyzed SQL> select name,height from index_stats where name='I_TEST_OBJECT_NAME'; ---查询index_stats之前需要 analyze ... validate structure，否则无数据 NAME HEIGHT ------------------------------ ---------- I_TEST_OBJECT_NAME 3 -------------------------------------------------------------------------------------------- Oracle 提供了分析 Btree index 结构的命令 treedump，在进行treedump之前需要获得索引的object_id -------------------------------------------------------------------------------------------- SQL> select object_id from dba_objects where object_name='I_TEST_OBJECT_NAME' and owner='ROBINSON'; OBJECT_ID ---------- 55178 SQL> ALTER SESSION SET EVENTS 'immediate trace name treedump level 55178'; Session altered ------------------------ treedump trace 文件 ------------------------ ----- begin tree dump branch: 0x1800014 25165844 (0: nrow: 2, level: 2) branch: 0x1800710 25167632 (-1: nrow: 247, level: 1) leaf: 0x1800015 25165845 (-1: nrow: 182 rrow: 182) leaf: 0x1800016 25165846 (0: nrow: 182 rrow: 182) leaf: 0x1800017 25165847 (1: nrow: 186 rrow: 186) leaf: 0x1800018 25165848 (2: nrow: 189 rrow: 189) leaf: 0x1800019 25165849 (3: nrow: 186 rrow: 186) leaf: 0x180001a 25165850 (4: nrow: 190 rrow: 190) leaf: 0x180001b 25165851 (5: nrow: 185 rrow: 185) leaf: 0x180001c 25165852 (6: nrow: 179 rrow: 179) leaf: 0x180001d 25165853 (7: nrow: 187 rrow: 187) leaf: 0x180001e 25165854 (8: nrow: 181 rrow: 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rrow: 249) leaf: 0x180071e 25167646 (13: nrow: 286 rrow: 286) leaf: 0x180071f 25167647 (14: nrow: 239 rrow: 239) leaf: 0x1800720 25167648 (15: nrow: 236 rrow: 236) leaf: 0x1800721 25167649 (16: nrow: 222 rrow: 222) leaf: 0x1800722 25167650 (17: nrow: 213 rrow: 213) leaf: 0x1800723 25167651 (18: nrow: 227 rrow: 227) leaf: 0x1800724 25167652 (19: nrow: 204 rrow: 204) leaf: 0x1800725 25167653 (20: nrow: 226 rrow: 226) leaf: 0x1800726 25167654 (21: nrow: 231 rrow: 231) leaf: 0x1800727 25167655 (22: nrow: 211 rrow: 211) leaf: 0x1800728 25167656 (23: nrow: 228 rrow: 228) leaf: 0x1800729 25167657 (24: nrow: 235 rrow: 235) leaf: 0x180072a 25167658 (25: nrow: 222 rrow: 222) leaf: 0x180072b 25167659 (26: nrow: 224 rrow: 224) leaf: 0x180072c 25167660 (27: nrow: 227 rrow: 227) leaf: 0x180072d 25167661 (28: nrow: 222 rrow: 222) leaf: 0x180072e 25167662 (29: nrow: 260 rrow: 260) leaf: 0x180072f 25167663 (30: nrow: 239 rrow: 239) leaf: 0x1800730 25167664 (31: nrow: 244 rrow: 244) leaf: 0x1800731 25167665 (32: nrow: 242 rrow: 242) leaf: 0x1800732 25167666 (33: nrow: 256 rrow: 256) leaf: 0x1800733 25167667 (34: nrow: 259 rrow: 259) leaf: 0x1800734 25167668 (35: nrow: 242 rrow: 242) leaf: 0x1800735 25167669 (36: nrow: 233 rrow: 233) leaf: 0x1800736 25167670 (37: nrow: 249 rrow: 249) leaf: 0x1800737 25167671 (38: nrow: 255 rrow: 255) leaf: 0x1800738 25167672 (39: nrow: 286 rrow: 286) leaf: 0x1800739 25167673 (40: nrow: 311 rrow: 311) leaf: 0x180073a 25167674 (41: nrow: 277 rrow: 277) leaf: 0x180073b 25167675 (42: nrow: 338 rrow: 338) leaf: 0x180073c 25167676 (43: nrow: 277 rrow: 277) leaf: 0x180073d 25167677 (44: nrow: 266 rrow: 266) leaf: 0x180073e 25167678 (45: nrow: 336 rrow: 336) leaf: 0x180073f 25167679 (46: nrow: 358 rrow: 358) leaf: 0x1800740 25167680 (47: nrow: 286 rrow: 286) leaf: 0x1800741 25167681 (48: nrow: 212 rrow: 212) leaf: 0x1800742 25167682 (49: nrow: 199 rrow: 199) leaf: 0x1800743 25167683 (50: nrow: 258 rrow: 258) leaf: 0x1800744 25167684 (51: nrow: 246 rrow: 246) leaf: 0x1800745 25167685 (52: nrow: 245 rrow: 245) leaf: 0x1800746 25167686 (53: nrow: 249 rrow: 249) leaf: 0x1800747 25167687 (54: nrow: 239 rrow: 239) leaf: 0x1800748 25167688 (55: nrow: 236 rrow: 236) leaf: 0x1800749 25167689 (56: nrow: 295 rrow: 295) leaf: 0x180074a 25167690 (57: nrow: 238 rrow: 238) leaf: 0x180074b 25167691 (58: nrow: 234 rrow: 234) leaf: 0x180074c 25167692 (59: nrow: 283 rrow: 283) leaf: 0x180074d 25167693 (60: nrow: 262 rrow: 262) leaf: 0x180074e 25167694 (61: nrow: 266 rrow: 266) leaf: 0x180074f 25167695 (62: nrow: 267 rrow: 267) leaf: 0x1800750 25167696 (63: nrow: 242 rrow: 242) leaf: 0x1800751 25167697 (64: nrow: 244 rrow: 244) leaf: 0x1800752 25167698 (65: nrow: 252 rrow: 252) leaf: 0x1800753 25167699 (66: nrow: 238 rrow: 238) leaf: 0x1800754 25167700 (67: nrow: 241 rrow: 241) leaf: 0x1800755 25167701 (68: nrow: 255 rrow: 255) leaf: 0x1800756 25167702 (69: nrow: 269 rrow: 269) leaf: 0x1800757 25167703 (70: nrow: 260 rrow: 260) leaf: 0x1800758 25167704 (71: nrow: 262 rrow: 262) leaf: 0x1800759 25167705 (72: nrow: 218 rrow: 218) leaf: 0x180075a 25167706 (73: nrow: 253 rrow: 253) leaf: 0x180075b 25167707 (74: nrow: 259 rrow: 259) leaf: 0x180075c 25167708 (75: nrow: 222 rrow: 222) leaf: 0x180075d 25167709 (76: nrow: 227 rrow: 227) leaf: 0x180075e 25167710 (77: nrow: 209 rrow: 209) leaf: 0x180075f 25167711 (78: nrow: 216 rrow: 216) leaf: 0x1800760 25167712 (79: nrow: 219 rrow: 219) leaf: 0x1800761 25167713 (80: nrow: 220 rrow: 220) leaf: 0x1800762 25167714 (81: nrow: 219 rrow: 219) leaf: 0x1800763 25167715 (82: nrow: 222 rrow: 222) leaf: 0x1800764 25167716 (83: nrow: 223 rrow: 223) leaf: 0x1800765 25167717 (84: nrow: 206 rrow: 206) leaf: 0x1800766 25167718 (85: nrow: 255 rrow: 255) leaf: 0x1800767 25167719 (86: nrow: 254 rrow: 254) leaf: 0x1800768 25167720 (87: nrow: 248 rrow: 248) leaf: 0x1800769 25167721 (88: nrow: 246 rrow: 246) leaf: 0x180076a 25167722 (89: nrow: 295 rrow: 295) leaf: 0x180076b 25167723 (90: nrow: 268 rrow: 268) leaf: 0x180076c 25167724 (91: nrow: 281 rrow: 281) leaf: 0x180076d 25167725 (92: nrow: 239 rrow: 239) leaf: 0x180076e 25167726 (93: nrow: 209 rrow: 209) leaf: 0x180076f 25167727 (94: nrow: 306 rrow: 306) leaf: 0x1800770 25167728 (95: nrow: 269 rrow: 269) leaf: 0x1800771 25167729 (96: nrow: 240 rrow: 240) leaf: 0x1800772 25167730 (97: nrow: 254 rrow: 254) leaf: 0x1800773 25167731 (98: nrow: 266 rrow: 266) leaf: 0x1800774 25167732 (99: nrow: 259 rrow: 259) leaf: 0x1800775 25167733 (100: nrow: 269 rrow: 269) leaf: 0x1800776 25167734 (101: nrow: 249 rrow: 249) leaf: 0x1800777 25167735 (102: nrow: 215 rrow: 215) leaf: 0x1800778 25167736 (103: nrow: 230 rrow: 230) leaf: 0x1800779 25167737 (104: nrow: 252 rrow: 252) leaf: 0x180077a 25167738 (105: nrow: 296 rrow: 296) leaf: 0x180077b 25167739 (106: nrow: 226 rrow: 226) leaf: 0x180077c 25167740 (107: nrow: 194 rrow: 194) leaf: 0x180077d 25167741 (108: nrow: 194 rrow: 194) leaf: 0x180077e 25167742 (109: nrow: 194 rrow: 194) leaf: 0x180077f 25167743 (110: nrow: 194 rrow: 194) leaf: 0x1800780 25167744 (111: nrow: 194 rrow: 194) leaf: 0x1800781 25167745 (112: nrow: 217 rrow: 217) leaf: 0x1800782 25167746 (113: nrow: 231 rrow: 231) leaf: 0x1800783 25167747 (114: nrow: 237 rrow: 237) leaf: 0x1800784 25167748 (115: nrow: 276 rrow: 276) leaf: 0x1800785 25167749 (116: nrow: 232 rrow: 232) leaf: 0x1800786 25167750 (117: nrow: 220 rrow: 220) leaf: 0x1800787 25167751 (118: nrow: 239 rrow: 239) leaf: 0x1800788 25167752 (119: nrow: 222 rrow: 222) leaf: 0x180078b 25167755 (120: nrow: 220 rrow: 220) leaf: 0x180078c 25167756 (121: nrow: 238 rrow: 238) leaf: 0x180078d 25167757 (122: nrow: 286 rrow: 286) leaf: 0x180078e 25167758 (123: nrow: 250 rrow: 250) leaf: 0x180078f 25167759 (124: nrow: 256 rrow: 256) leaf: 0x1800790 25167760 (125: nrow: 261 rrow: 261) leaf: 0x1800791 25167761 (126: nrow: 249 rrow: 249) leaf: 0x1800792 25167762 (127: nrow: 246 rrow: 246) leaf: 0x1800793 25167763 (128: nrow: 243 rrow: 243) leaf: 0x1800794 25167764 (129: nrow: 227 rrow: 227) leaf: 0x1800795 25167765 (130: nrow: 216 rrow: 216) leaf: 0x1800796 25167766 (131: nrow: 235 rrow: 235) leaf: 0x1800797 25167767 (132: nrow: 229 rrow: 229) leaf: 0x1800798 25167768 (133: nrow: 230 rrow: 230) leaf: 0x1800799 25167769 (134: nrow: 224 rrow: 224) leaf: 0x180079a 25167770 (135: nrow: 219 rrow: 219) leaf: 0x180079b 25167771 (136: nrow: 268 rrow: 268) leaf: 0x180079c 25167772 (137: nrow: 242 rrow: 242) leaf: 0x180079d 25167773 (138: nrow: 203 rrow: 203) leaf: 0x180079e 25167774 (139: nrow: 200 rrow: 200) leaf: 0x180079f 25167775 (140: nrow: 184 rrow: 184) leaf: 0x18007a0 25167776 (141: nrow: 177 rrow: 177) leaf: 0x18007a1 25167777 (142: nrow: 182 rrow: 182) leaf: 0x18007a2 25167778 (143: nrow: 214 rrow: 214) leaf: 0x18007a3 25167779 (144: nrow: 217 rrow: 217) leaf: 0x18007a4 25167780 (145: nrow: 222 rrow: 222) leaf: 0x18007a5 25167781 (146: nrow: 189 rrow: 189) leaf: 0x18007a6 25167782 (147: nrow: 190 rrow: 190) leaf: 0x18007a7 25167783 (148: nrow: 185 rrow: 185) leaf: 0x18007a8 25167784 (149: nrow: 197 rrow: 197) leaf: 0x18007a9 25167785 (150: nrow: 203 rrow: 203) leaf: 0x18007aa 25167786 (151: nrow: 197 rrow: 197) leaf: 0x18007ab 25167787 (152: nrow: 210 rrow: 210) leaf: 0x18007ac 25167788 (153: nrow: 211 rrow: 211) leaf: 0x18007ad 25167789 (154: nrow: 195 rrow: 195) leaf: 0x18007ae 25167790 (155: nrow: 209 rrow: 209) leaf: 0x18007af 25167791 (156: nrow: 192 rrow: 192) leaf: 0x18007b0 25167792 (157: nrow: 192 rrow: 192) leaf: 0x18007b1 25167793 (158: nrow: 193 rrow: 193) leaf: 0x18007b2 25167794 (159: nrow: 208 rrow: 208) leaf: 0x18007b3 25167795 (160: nrow: 200 rrow: 200) leaf: 0x18007b4 25167796 (161: nrow: 206 rrow: 206) leaf: 0x18007b5 25167797 (162: nrow: 216 rrow: 216) leaf: 0x18007b6 25167798 (163: nrow: 186 rrow: 186) leaf: 0x18007b7 25167799 (164: nrow: 183 rrow: 183) leaf: 0x18007b8 25167800 (165: nrow: 202 rrow: 202) leaf: 0x18007b9 25167801 (166: nrow: 200 rrow: 200) leaf: 0x18007ba 25167802 (167: nrow: 199 rrow: 199) leaf: 0x18007bb 25167803 (168: nrow: 184 rrow: 184) leaf: 0x18007bc 25167804 (169: nrow: 188 rrow: 188) leaf: 0x18007bd 25167805 (170: nrow: 188 rrow: 188) leaf: 0x18007be 25167806 (171: nrow: 182 rrow: 182) leaf: 0x18007bf 25167807 (172: nrow: 192 rrow: 192) leaf: 0x18007c0 25167808 (173: nrow: 198 rrow: 198) leaf: 0x18007c1 25167809 (174: nrow: 210 rrow: 210) leaf: 0x18007c2 25167810 (175: nrow: 195 rrow: 195) leaf: 0x18007c3 25167811 (176: nrow: 186 rrow: 186) leaf: 0x18007c4 25167812 (177: nrow: 183 rrow: 183) leaf: 0x18007c5 25167813 (178: nrow: 183 rrow: 183) leaf: 0x18007c6 25167814 (179: nrow: 209 rrow: 209) leaf: 0x18007c7 25167815 (180: nrow: 197 rrow: 197) leaf: 0x18007c8 25167816 (181: nrow: 201 rrow: 201) leaf: 0x18007c9 25167817 (182: nrow: 184 rrow: 184) leaf: 0x18007ca 25167818 (183: nrow: 184 rrow: 184) leaf: 0x18007cb 25167819 (184: nrow: 184 rrow: 184) leaf: 0x18007cc 25167820 (185: nrow: 180 rrow: 180) leaf: 0x18007cd 25167821 (186: nrow: 178 rrow: 178) leaf: 0x18007ce 25167822 (187: nrow: 179 rrow: 179) leaf: 0x18007cf 25167823 (188: nrow: 179 rrow: 179) leaf: 0x18007d0 25167824 (189: nrow: 179 rrow: 179) leaf: 0x18007d1 25167825 (190: nrow: 180 rrow: 180) leaf: 0x18007d2 25167826 (191: nrow: 183 rrow: 183) leaf: 0x18007d3 25167827 (192: nrow: 178 rrow: 178) leaf: 0x18007d4 25167828 (193: nrow: 179 rrow: 179) leaf: 0x18007d5 25167829 (194: nrow: 186 rrow: 186) leaf: 0x18007d6 25167830 (195: nrow: 191 rrow: 191) leaf: 0x18007d7 25167831 (196: nrow: 203 rrow: 203) leaf: 0x18007d8 25167832 (197: nrow: 190 rrow: 190) leaf: 0x18007d9 25167833 (198: nrow: 186 rrow: 186) leaf: 0x18007da 25167834 (199: nrow: 185 rrow: 185) leaf: 0x18007db 25167835 (200: nrow: 183 rrow: 183) leaf: 0x18007dc 25167836 (201: nrow: 198 rrow: 198) leaf: 0x18007dd 25167837 (202: nrow: 208 rrow: 208) leaf: 0x18007de 25167838 (203: nrow: 184 rrow: 184) leaf: 0x18007df 25167839 (204: nrow: 183 rrow: 183) leaf: 0x18007e0 25167840 (205: nrow: 186 rrow: 186) leaf: 0x18007e1 25167841 (206: nrow: 189 rrow: 189) leaf: 0x18007e2 25167842 (207: nrow: 181 rrow: 181) leaf: 0x18007e3 25167843 (208: nrow: 181 rrow: 181) leaf: 0x18007e4 25167844 (209: nrow: 193 rrow: 193) leaf: 0x18007e5 25167845 (210: nrow: 197 rrow: 197) leaf: 0x18007e6 25167846 (211: nrow: 186 rrow: 186) leaf: 0x18007e7 25167847 (212: nrow: 189 rrow: 189) leaf: 0x18007e8 25167848 (213: nrow: 201 rrow: 201) leaf: 0x18007e9 25167849 (214: nrow: 201 rrow: 201) leaf: 0x18007ea 25167850 (215: nrow: 183 rrow: 183) leaf: 0x18007eb 25167851 (216: nrow: 196 rrow: 196) leaf: 0x18007ec 25167852 (217: nrow: 178 rrow: 178) leaf: 0x18007ed 25167853 (218: nrow: 183 rrow: 183) leaf: 0x18007ee 25167854 (219: nrow: 180 rrow: 180) leaf: 0x18007ef 25167855 (220: nrow: 196 rrow: 196) leaf: 0x18007f0 25167856 (221: nrow: 197 rrow: 197) leaf: 0x18007f1 25167857 (222: nrow: 197 rrow: 197) leaf: 0x18007f2 25167858 (223: nrow: 194 rrow: 194) leaf: 0x18007f3 25167859 (224: nrow: 190 rrow: 190) leaf: 0x18007f4 25167860 (225: nrow: 193 rrow: 193) leaf: 0x18007f5 25167861 (226: nrow: 207 rrow: 207) leaf: 0x18007f6 25167862 (227: nrow: 202 rrow: 202) leaf: 0x18007f7 25167863 (228: nrow: 194 rrow: 194) leaf: 0x18007f8 25167864 (229: nrow: 207 rrow: 207) leaf: 0x18007f9 25167865 (230: nrow: 204 rrow: 204) leaf: 0x18007fa 25167866 (231: nrow: 194 rrow: 194) leaf: 0x18007fb 25167867 (232: nrow: 185 rrow: 185) leaf: 0x18007fc 25167868 (233: nrow: 208 rrow: 208) leaf: 0x18007fd 25167869 (234: nrow: 218 rrow: 218) leaf: 0x18007fe 25167870 (235: nrow: 194 rrow: 194) leaf: 0x18007ff 25167871 (236: nrow: 192 rrow: 192) leaf: 0x1800800 25167872 (237: nrow: 200 rrow: 200) leaf: 0x1800801 25167873 (238: nrow: 191 rrow: 191) leaf: 0x1800802 25167874 (239: nrow: 186 rrow: 186) leaf: 0x1800803 25167875 (240: nrow: 181 rrow: 181) leaf: 0x1800804 25167876 (241: nrow: 182 rrow: 182) leaf: 0x1800805 25167877 (242: nrow: 182 rrow: 182) leaf: 0x1800806 25167878 (243: nrow: 190 rrow: 190) leaf: 0x1800807 25167879 (244: nrow: 191 rrow: 191) leaf: 0x1800808 25167880 (245: nrow: 180 rrow: 180) leaf: 0x180080b 25167883 (246: nrow: 55 rrow: 55) ----- end tree dump ------------------ 解释 treedump 输出 ------------------ branch 表示的是 branch block ，它后面跟了一个十六进制表示的DBA(data block address)，以及用10进制表示的DBA DBA 之后表示在同一层次的相对位置(root 从0开始,branch 以及leaf从 -1开始) nrow 表示块中包含了多少条目(包括delete的条目) rrow 表示块中包含的实际条目(不包括delete的条目) level 表示从该block到leaf的深度(leaf没有 level) branch: 0x1800014 25165844 (0: nrow: 2, level: 2) 这个 branch block 的 level 为2，也就是说从这个branch block 到 leaf block 的深度为2,根据前面的查询，这个索引的Blevel为2,所以这个 branch其实是 root block. 其实根据 nrow:2 也可以看出来它是root block，因为nrow:2 说明它只包含了2个条目，那么这2个条目其实就是dump 文件中的其他2个 branch block 的条目现在我来验证一下 branch: 0x1800014 25165844 (0: nrow: 2, level: 2) 是不是 root block , 我查询这个 branch 的 DBA SQL> select dbms_utility.data_block_address_file('25165844') FILE_ID, 2 dbms_utility.data_block_address_block('25165844') BLOCK_ID from dual; FILE_ID BLOCK_ID ---------- ---------- 6 20 Btree 索引的 root block总是segment header+1,所以我查询该索引的段头 SQL> select header_file,header_block from dba_segments where segment_name='I_TEST_OBJECT_NAME'; HEADER_FILE HEADER_BLOCK ----------- ------------ 6 19 那么现在已经证明了 branch: 0x1800014 25165844 (0: nrow: 2, level: 2) 是root block, 其实 treedump第一个 branch block 就是 root block branch: 0x1800710 25167632 (-1: nrow: 247, level: 1) 这个branch 的 DBA为0x1800710(十六进制)，25167632(十进制) -1 表示它是与它在同一个深度的 branch block中的第一个 branch block nrow: 247表示它有247个 leaf block. level: 1 表示这个 branch block 到 leaf block的深度为1 leaf: 0x1800015 25165845 (-1: nrow: 182 rrow: 182) leaf 表示它是一个 leaf block 0x1800015 25165845 分别是这个 leaf block 的十六进制/十进制的 DBA -1 表示它是 leaf block 中的第一个 block nrow: 182 表示它一共有182条记录 rrow: 182 表示它实际有182条记录 ----------------- branch block dump ----------------- 这里选择dump branch: 0x1800710 25167632 (-1: nrow: 247, level: 1) SQL> select dbms_utility.data_block_address_file('25167632') FILE_ID, 2 dbms_utility.data_block_address_block('25167632') BLOCK_ID from dual; FILE_ID BLOCK_ID ---------- ---------- 6 1808 SQL> alter system dump datafile 6 block 1808; System altered. 部分 DUMP 文件 Block header dump: 0x01800710 Object id on Block? Y seg/obj: 0xd78a csc: 0x00.17bbef0 itc: 1 flg: E typ: 2 - INDEX brn: 0 bdba: 0x1800709 ver: 0x01 opc: 0 inc: 0 exflg: 0 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0xffff.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.017bbef0 Branch block dump ================= header address 156329548=0x951664c kdxcolev 1 KDXCOLEV Flags = - - - kdxcolok 0 kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y kdxconco 2 kdxcosdc 0 kdxconro 246 kdxcofbo 520=0x208 kdxcofeo 549=0x225 kdxcoavs 29 kdxbrlmc 25165845=0x1800015 kdxbrsno 0 kdxbrbksz 8060 kdxbr2urrc 15 row#0[8027] dba: 25165846=0x1800016 col 0; len 24; (24): 2f 31 30 64 65 32 32 63 36 5f 43 6c 61 73 73 54 79 70 65 49 6d 70 6c 32 col 1; len 3; (3): 01 80 03 row#1[7988] dba: 25165847=0x1800017 col 0; len 30; (30): 2f 31 31 64 35 30 39 31 32 5f 44 61 74 65 46 6f 72 6d 61 74 5a 6f 6e 65 44 61 74 61 5f 7a col 1; len 3; (3): 01 80 04 row#2[7977] dba: 25165848=0x1800018 col 0; len 5; (5): 2f 31 32 61 32 col 1; TERM ..................................省略.................................. row#245[549] dba: 25167630=0x180070e col 0; len 10; (10): 41 4c 4c 24 4f 4c 41 50 5f 44 col 1; TERM ----- end of branch block dump ----- End dump data blocks tsn: 7 file#: 6 minblk 1808 maxblk 1808 ---------------- 解释部分dump输出 ---------------- kdxcolev 1 --该block到leaf block的深度(leaf block 为0).这里branch block 的level 为1 与前面查询相吻合 KDXCOLEV Flags = - - - kdxcolok 0 --表示是否有事务lock了这个branch block，如果有有多少事务 kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y kdxconco 2 --索引值条目. 这里表示有2个条目 kdxcosdc 0 --这个block的结构被更改次数.这里0表示没有更改 kdxconro 246 --索引条目(不包含kdxbrlmc 指针) kdxcofbo 520=0x208 --空闲空间的起始偏移量 kdxcofeo 549=0x225 --空闲空间的末尾偏移量 kdxcoavs 29 --block中的空闲空间=kdxcofeo-kdxcofbo kdxbrlmc 25165845=0x1800015 --如果index value小于row#0，指向该 block 的地址 kdxbrsno 0 --最后被更改的索引条目 kdxbrbksz 8060 --块中的可用空间 kdxbr2urrc 15 row#2[7977] dba: 25165848=0x1800018 --row# 表示索引条目数，从0开始，紧接着就是十进制和十六进制的DBA，该DBA指向 leaf block col 0; len 5; (5): 2f 31 32 61 32 --列的行号，从0开始，紧接着的就是列的长度以及列的值，那么这个值称之为separator key，这个separator key 可以区分真实的索引值，所以从这里我们也知道 branch block不会存储完整的索引值，只要能区分就行 col 1; TERM --------------- leaf block DUMP --------------- 这里选择 dump row#2[7977] dba: 25165848=0x1800018 ，因为它包含的索引键很少 dump 之前先看一下 row#2[7977] 存储了什么索引键 2f 表示 / 31 表示 1 32 表示 2 61 表示 a 具体转换过程如下 SQL> declare n varchar2(2000); 2 begin 3 dbms_stats.convert_raw_value('2f',n); 4 dbms_output.put_line(n); 5 end; 6 / / PL/SQL procedure successfully completed. SQL> select dbms_utility.data_block_address_file('25165848') FILE_ID, 2 dbms_utility.data_block_address_block('25165848') BLOCK_ID from dual; FILE_ID BLOCK_ID ---------- ---------- 6 24 SQL> alter system dump datafile 6 block 24; System altered. 部分DUMP文件 Block header dump: 0x01800018 Object id on Block? Y seg/obj: 0xd78a csc: 0x00.17bbef0 itc: 2 flg: E typ: 2 - INDEX brn: 0 bdba: 0x1800011 ver: 0x01 opc: 0 inc: 0 exflg: 0 Itl Xid Uba Flag Lck Scn/Fsc 0x01 0x0000.000.00000000 0x00000000.0000.00 ---- 0 fsc 0x0000.00000000 0x02 0xffff.000.00000000 0x00000000.0000.00 C--- 0 scn 0x0000.017bbef0 Leaf block dump =============== header address 146564708=0x8bc6664 kdxcolev 0 KDXCOLEV Flags = - - - kdxcolok 0 kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y kdxconco 2 kdxcosdc 0 kdxconro 189 kdxcofbo 414=0x19e kdxcofeo 1248=0x4e0 kdxcoavs 834 kdxlespl 0 kdxlende 0 kdxlenxt 25165849=0x1800019 kdxleprv 25165847=0x1800017 kdxledsz 0 kdxlebksz 8036 row#0[7996] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 00 e2 00 16 row#1[7956] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 00 e2 00 17 row#2[7916] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 03 b5 00 25 row#3[7876] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 03 b5 00 26 row#4[7836] flag: ------, lock: 0, len=40 ..................................省略.................................. row#188[1248] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 33 38 35 32 32 37 66 5f 4d 61 70 52 65 67 69 6f 6e 43 6f 6e 74 61 69 6e 6d 65 6e 74 col 1; len 6; (6): 01 80 01 6a 00 00 ----- end of leaf block dump ----- End dump data blocks tsn: 7 file#: 6 minblk 24 maxblk 24 ---------------- 解释部分dump输出 ---------------- kdxcolev 0 --该block到leaf block的深度(leaf block 为0). KDXCOLEV Flags = - - - kdxcolok 0 --表示是否有事务lock了这个branch block，如果有有多少事务 kdxcoopc 0x80: opcode=0: iot flags=--- is converted=Y kdxconco 2 --索引值条目. 这里表示有2个条目 kdxcosdc 0 --这个block的结构被更改次数.这里0表示没有更改 kdxconro 189 --索引条目 ,这里有189个索引条目它等于 row#188-row#0+1 kdxcofbo 414=0x19e --空闲空间的起始偏移量 kdxcofeo 1248=0x4e0 --空闲空间的末尾偏移量 kdxcoavs 834 --block中的空闲空间=kdxcofeo-kdxcofbo kdxlespl 0 --block split的时候没有commit的记录的大小(byte) kdxlende 0 --被删除的条目 kdxlenxt 25165849=0x1800019 --指向下一个 leaf block的指针(DBA) kdxleprv 25165847=0x1800017 --指向上一个 leaf block的指针(DBA) kdxledsz 0 --被删除的空间 kdxlebksz 8036 --可用空间 row#0[7996] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 00 e2 00 16 row# 表示索引值的条目，从0开始 lock: 0 表示ITL中的锁信息 0表示没有被锁 len=40 表示索引值长度 col 表示列号，从0开始那么接下来就是索引的键值以及 rowid中后12位值下面我们来看一下row#0存储的值是什么 SQL> declare n varchar2(2000); 2 begin 3 dbms_stats.convert_raw_value('2f31326132373365365f496e7465726e6174696f6e616c466f726d617474',n); 4 dbms_output.put_line(n); 5 end; 6 / /12a273e6_InternationalFormatt PL/SQL procedure successfully completed. ROWID一共用18位表示最前6位表示 data object number 之后后3位表示 datafile number 之后后6位表示 datablock number 最后3位表示 row number 所以这里的rowid其实只是除去了 data object number的一部分而已 SQL> select to_number('18000e2','xxxxxxxxxxxxxxxx') from dual; TO_NUMBER('18000E2','XXXXXXXXX ------------------------------ 25166050 SQL> select dbms_utility.data_block_address_file('25166050') FILE_ID,dbms_utility.data_block_address_block('25166050') BLOCK_ID from dual; FILE_ID BLOCK_ID ---------- ---------- 6 226 SQL> select dbms_rowid.rowid_relative_fno(rowid)file_id, dbms_rowid.rowid_block_number(rowid)block_id,dbms_rowid.rowid_row_number(rowid) row# 2 from test where object_name='/12a273e6_InternationalFormatt'; FILE_ID BLOCK_ID ROW# ---------- ---------- ---------- 6 226 22 6 226 23 6 949 37 6 949 38 根据这个还原的值我来查询一下 SQL> select owner,object_name,rowid from test where object_name='/12a273e6_InternationalFormatt'; OWNER OBJECT_NAME ROWID ------------------------------ ------------------------------ ------------------ SYS /12a273e6_InternationalFormatt AAANeJAAGAAAADiAAW PUBLIC /12a273e6_InternationalFormatt AAANeJAAGAAAADiAAX SYS /12a273e6_InternationalFormatt AAANeJAAGAAAAO1AAl PUBLIC /12a273e6_InternationalFormatt AAANeJAAGAAAAO1AAm SQL> select owner,object_name,dump(rowid,16) from test where object_name='/12a273e6_InternationalFormatt'; OWNER OBJECT_NAME DUMP(ROWID,16) ---------- ----------------------------------- -------------------------------------------------------------------------------- SYS /12a273e6_InternationalFormatt Typ=69 Len=10: 0,0,d7,89,1,80,0,e2,0,16 PUBLIC /12a273e6_InternationalFormatt Typ=69 Len=10: 0,0,d7,89,1,80,0,e2,0,17 SYS /12a273e6_InternationalFormatt Typ=69 Len=10: 0,0,d7,89,1,80,3,b5,0,25 PUBLIC /12a273e6_InternationalFormatt Typ=69 Len=10: 0,0,d7,89,1,80,3,b5,0,26 回忆一下 branch block row#2[7977] dba: 25165848=0x1800018 col 0; len 5; (5): 2f 31 32 61 32 -------它正是真正的索引键的前缀 col 1; TERM row#0[7996] flag: ------, lock: 0, len=40 col 0; len 30; (30): 2f 31 32 61 32 37 33 65 36 5f 49 6e 74 65 72 6e 61 74 69 6f 6e 61 6c 46 6f 72 6d 61 74 74 col 1; len 6; (6): 01 80 00 e2 00 16 之所以Oracle在 Branch block中只记录索引键值的前缀，而不是所有值，是因为这样可以节约空间，从而能够存储更多的索引条目同时，我们也能理解了为什么查询使用 like '%xxx' 这种方法不会走Btree 索引，因为Branch block 存储的是前缀.

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