1 /* 2 * Copyright (c) 2007 The DragonFly Project. All rights reserved. 3 * 4 * This code is derived from software contributed to The DragonFly Project 5 * by Matthew Dillon <dillon@backplane.com> 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in 15 * the documentation and/or other materials provided with the 16 * distribution. 17 * 3. Neither the name of The DragonFly Project nor the names of its 18 * contributors may be used to endorse or promote products derived 19 * from this software without specific, prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 * 34 * $DragonFly: src/sys/vfs/hammer/hammer_btree.h,v 1.12 2008/02/10 09:51:01 dillon Exp $ 35 */ 36 37 /* 38 * HAMMER B-Tree index 39 * 40 * HAMMER implements a modified B+Tree. B+Trees store records only 41 * at their leaves and HAMMER's modification is to adjust the internal 42 * elements so there is a boundary element on each side instead of sub-tree 43 * pointers. 44 * 45 * We just call our modified B+Tree a 'B-Tree' in HAMMER documentation to 46 * reduce confusion. 47 * 48 * A B-Tree internal node looks like this: 49 * 50 * B N N N N N N B <-- boundary and internal elements 51 * S S S S S S S <-- subtree pointers 52 * 53 * A B-Tree leaf node looks like this: 54 * 55 * L L L L L L L L <-- leaf elemenets 56 * (there is also a previous and next-leaf pointer) 57 * 58 * The recursion radix of an internal node is reduced by 1 relative to 59 * a normal B-Tree in order to accomodate the right-hand boundary. 60 * 61 * The big benefit to using a B-Tree with built-in bounds information is 62 * that it makes it possible to cache pointers into the middle of the tree 63 * and not have to start searches, insertions, OR deletions at the root node. 64 * The boundary elements allow searches to progress in a definitive direction 65 * from any point in the tree without revisting nodes. It is also possible 66 * to terminate searches early and make minor adjustments to the boundaries 67 * (within the confines of the parent's boundaries) on the fly. This greatly 68 * improves the efficiency of many operations, most especially record appends. 69 * 70 * HAMMER B-Trees are per-cluster. The global multi-cluster B-Tree is 71 * constructed by allowing internal nodes to link to the roots of other 72 * clusters. Fields in the cluster header then reference back to its 73 * parent and use the cluster generation number to detect stale linkages. 74 * 75 * The B-Tree balancing code can operate within a cluster or across the 76 * filesystem's ENTIRE B-Tree super-structure. A cluster's B-Tree root 77 * can be a leaf node in the worse case. A cluster is guarenteed to have 78 * sufficient free space to hold a single completely full leaf in the 79 * degenerate case. 80 * 81 * All of the structures below are on-disk structures. 82 */ 83 84 /* 85 * Common base for all B-Tree element types (40 bytes) 86 * 87 * obj_type is set to the object type the record represents if an inode, 88 * directory entry, or an inter-cluster reference. A cluster range is 89 * special in that the B-Tree nodes represent a range within the B-Tree 90 * inclusive of rec_type field, so obj_type must be used to detect the 91 * cluster range entries. 92 * 93 * btype is only used by the elements making up an internal or leaf B-Tree 94 * node and applies to the node rather then to the key. This means that 95 * btype must be assigned/reassigned after any update to the base_elm making 96 * up a B-Tree element. 97 */ 98 struct hammer_base_elm { 99 int64_t obj_id; /* 00 object record is associated with */ 100 int64_t key; /* 08 indexing key (offset or namekey) */ 101 102 hammer_tid_t create_tid; /* 10 transaction id for record creation */ 103 hammer_tid_t delete_tid; /* 18 transaction id for record update/del */ 104 105 u_int16_t rec_type; /* 20 _RECTYPE_ */ 106 u_int8_t obj_type; /* 22 _OBJTYPE_ (restricted) */ 107 u_int8_t btype; /* 23 B-Tree element type */ 108 int32_t reserved07; /* 24 (future) */ 109 /* 28 */ 110 }; 111 112 typedef struct hammer_base_elm *hammer_base_elm_t; 113 114 /* 115 * Internal element (40 + 24 = 64 bytes). 116 * 117 * An internal element contains the left-hand boundary, right-hand boundary, 118 * and a recursion to another B-Tree node. 119 */ 120 struct hammer_btree_internal_elm { 121 struct hammer_base_elm base; 122 hammer_off_t unused00; 123 hammer_off_t subtree_offset; 124 int32_t unused02; 125 int32_t unused03; 126 }; 127 128 /* 129 * Leaf B-Tree element (40 + 24 = 64 bytes). 130 * 131 * A leaf element. 132 */ 133 struct hammer_btree_leaf_elm { 134 struct hammer_base_elm base; 135 hammer_off_t rec_offset; 136 hammer_off_t data_offset; 137 int32_t data_len; 138 u_int32_t data_crc; 139 }; 140 141 /* 142 * Rollup btree leaf element types - 64 byte structure 143 */ 144 union hammer_btree_elm { 145 struct hammer_base_elm base; 146 struct hammer_btree_leaf_elm leaf; 147 struct hammer_btree_internal_elm internal; 148 }; 149 150 typedef union hammer_btree_elm *hammer_btree_elm_t; 151 152 /* 153 * B-Tree node (normal or meta) (16x64 = 1K structure) 154 * 155 * Each node contains 15 elements. The last element for an internal node 156 * is the right-boundary so internal nodes have one fewer logical elements 157 * then leaf nodes. 158 * 159 * 'count' always refers to the number of elements and is non-inclusive of 160 * the right-hand boundary for an internal node. 161 * 162 * NOTE: The node head for an internal does not contain the subtype 163 * (The B-Tree node type for the nodes referenced by its elements). 164 * Instead, each element specifies the subtype (elm->base.subtype). 165 * This allows us to maintain an unbalanced B-Tree and to easily identify 166 * special inter-cluster link elements. 167 * 168 * NOTE: FUTURE EXPANSION: The reserved fields in hammer_node_ondisk are 169 * reserved for left/right leaf linkage fields, flags, and other future 170 * features. 171 */ 172 #define HAMMER_BTREE_LEAF_ELMS 15 173 #define HAMMER_BTREE_INT_ELMS (HAMMER_BTREE_LEAF_ELMS - 1) 174 175 /* 176 * It is safe to combine two adjacent nodes if the total number of elements 177 * is less then or equal to the *_FILL constant. 178 */ 179 #define HAMMER_BTREE_LEAF_FILL (HAMMER_BTREE_LEAF_ELMS - 3) 180 #define HAMMER_BTREE_INT_FILL (HAMMER_BTREE_INT_ELMS - 3) 181 182 #define HAMMER_BTREE_TYPE_INTERNAL ((u_int8_t)'I') 183 #define HAMMER_BTREE_TYPE_LEAF ((u_int8_t)'L') 184 #define HAMMER_BTREE_TYPE_RECORD ((u_int8_t)'R') 185 186 struct hammer_node_ondisk { 187 /* 188 * B-Tree node header (64 bytes) 189 */ 190 u_int32_t signature; 191 u_int32_t crc; 192 hammer_off_t parent; /* 0 if at root of cluster */ 193 int32_t count; 194 u_int8_t type; 195 u_int8_t reserved01; 196 u_int16_t reserved02; 197 hammer_off_t reserved03; /* future link_left */ 198 hammer_off_t reserved04; /* future link_right */ 199 hammer_off_t reserved05; 200 hammer_off_t reserved06; 201 hammer_off_t reserved07; 202 203 /* 204 * Element array. Internal nodes have one less logical element 205 * (meaning: the same number of physical elements) in order to 206 * accomodate the right-hand boundary. The left-hand boundary 207 * is integrated into the first element. Leaf nodes have no 208 * boundary elements. 209 */ 210 union hammer_btree_elm elms[HAMMER_BTREE_LEAF_ELMS]; 211 }; 212 213 typedef struct hammer_node_ondisk *hammer_node_ondisk_t; 214 215