1 /*-
2 * Copyright (c) 1990, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Mike Olson.
7 *
8 * %sccs.include.redist.c%
9 */
10
11 #if defined(LIBC_SCCS) && !defined(lint)
12 static char sccsid[] = "@(#)bt_overflow.c 8.2 (Berkeley) 02/21/94";
13 #endif /* LIBC_SCCS and not lint */
14
15 #include <sys/param.h>
16
17 #include <stdio.h>
18 #include <stdlib.h>
19 #include <string.h>
20
21 #include <db.h>
22 #include "btree.h"
23
24 /*
25 * Big key/data code.
26 *
27 * Big key and data entries are stored on linked lists of pages. The initial
28 * reference is byte string stored with the key or data and is the page number
29 * and size. The actual record is stored in a chain of pages linked by the
30 * nextpg field of the PAGE header.
31 *
32 * The first page of the chain has a special property. If the record is used
33 * by an internal page, it cannot be deleted and the P_PRESERVE bit will be set
34 * in the header.
35 *
36 * XXX
37 * A single DBT is written to each chain, so a lot of space on the last page
38 * is wasted. This is a fairly major bug for some data sets.
39 */
40
41 /*
42 * __OVFL_GET -- Get an overflow key/data item.
43 *
44 * Parameters:
45 * t: tree
46 * p: pointer to { pgno_t, size_t }
47 * buf: storage address
48 * bufsz: storage size
49 *
50 * Returns:
51 * RET_ERROR, RET_SUCCESS
52 */
53 int
__ovfl_get(t,p,ssz,buf,bufsz)54 __ovfl_get(t, p, ssz, buf, bufsz)
55 BTREE *t;
56 void *p;
57 size_t *ssz;
58 char **buf;
59 size_t *bufsz;
60 {
61 PAGE *h;
62 pgno_t pg;
63 size_t nb, plen, sz;
64
65 memmove(&pg, p, sizeof(pgno_t));
66 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(size_t));
67 *ssz = sz;
68
69 #ifdef DEBUG
70 if (pg == P_INVALID || sz == 0)
71 abort();
72 #endif
73 /* Make the buffer bigger as necessary. */
74 if (*bufsz < sz) {
75 if ((*buf = (char *)realloc(*buf, sz)) == NULL)
76 return (RET_ERROR);
77 *bufsz = sz;
78 }
79
80 /*
81 * Step through the linked list of pages, copying the data on each one
82 * into the buffer. Never copy more than the data's length.
83 */
84 plen = t->bt_psize - BTDATAOFF;
85 for (p = *buf;; p = (char *)p + nb, pg = h->nextpg) {
86 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
87 return (RET_ERROR);
88
89 nb = MIN(sz, plen);
90 memmove(p, (char *)h + BTDATAOFF, nb);
91 mpool_put(t->bt_mp, h, 0);
92
93 if ((sz -= nb) == 0)
94 break;
95 }
96 return (RET_SUCCESS);
97 }
98
99 /*
100 * __OVFL_PUT -- Store an overflow key/data item.
101 *
102 * Parameters:
103 * t: tree
104 * data: DBT to store
105 * pgno: storage page number
106 *
107 * Returns:
108 * RET_ERROR, RET_SUCCESS
109 */
110 int
__ovfl_put(t,dbt,pg)111 __ovfl_put(t, dbt, pg)
112 BTREE *t;
113 const DBT *dbt;
114 pgno_t *pg;
115 {
116 PAGE *h, *last;
117 void *p;
118 pgno_t npg;
119 size_t nb, plen, sz;
120
121 /*
122 * Allocate pages and copy the key/data record into them. Store the
123 * number of the first page in the chain.
124 */
125 plen = t->bt_psize - BTDATAOFF;
126 for (last = NULL, p = dbt->data, sz = dbt->size;;
127 p = (char *)p + plen, last = h) {
128 if ((h = __bt_new(t, &npg)) == NULL)
129 return (RET_ERROR);
130
131 h->pgno = npg;
132 h->nextpg = h->prevpg = P_INVALID;
133 h->flags = P_OVERFLOW;
134 h->lower = h->upper = 0;
135
136 nb = MIN(sz, plen);
137 memmove((char *)h + BTDATAOFF, p, nb);
138
139 if (last) {
140 last->nextpg = h->pgno;
141 mpool_put(t->bt_mp, last, MPOOL_DIRTY);
142 } else
143 *pg = h->pgno;
144
145 if ((sz -= nb) == 0) {
146 mpool_put(t->bt_mp, h, MPOOL_DIRTY);
147 break;
148 }
149 }
150 return (RET_SUCCESS);
151 }
152
153 /*
154 * __OVFL_DELETE -- Delete an overflow chain.
155 *
156 * Parameters:
157 * t: tree
158 * p: pointer to { pgno_t, size_t }
159 *
160 * Returns:
161 * RET_ERROR, RET_SUCCESS
162 */
163 int
__ovfl_delete(t,p)164 __ovfl_delete(t, p)
165 BTREE *t;
166 void *p;
167 {
168 PAGE *h;
169 pgno_t pg;
170 size_t plen, sz;
171
172 memmove(&pg, p, sizeof(pgno_t));
173 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(size_t));
174
175 #ifdef DEBUG
176 if (pg == P_INVALID || sz == 0)
177 abort();
178 #endif
179 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
180 return (RET_ERROR);
181
182 /* Don't delete chains used by internal pages. */
183 if (h->flags & P_PRESERVE) {
184 mpool_put(t->bt_mp, h, 0);
185 return (RET_SUCCESS);
186 }
187
188 /* Step through the chain, calling the free routine for each page. */
189 for (plen = t->bt_psize - BTDATAOFF;; sz -= plen) {
190 pg = h->nextpg;
191 __bt_free(t, h);
192 if (sz <= plen)
193 break;
194 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
195 return (RET_ERROR);
196 }
197 return (RET_SUCCESS);
198 }
199