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32 * @(#)bt_overflow.c 8.5 (Berkeley) 7/16/94
33 * $DragonFly: src/lib/libc/db/btree/bt_overflow.c,v 1.4 2005/11/12 23:01:54 swildner Exp $
36 #include <sys/param.h>
48 * Big key and data entries are stored on linked lists of pages. The initial
49 * reference is byte string stored with the key or data and is the page number
50 * and size. The actual record is stored in a chain of pages linked by the
51 * nextpg field of the PAGE header.
53 * The first page of the chain has a special property. If the record is used
54 * by an internal page, it cannot be deleted and the P_PRESERVE bit will be set
58 * A single DBT is written to each chain, so a lot of space on the last page
59 * is wasted. This is a fairly major bug for some data sets.
63 * __OVFL_GET -- Get an overflow key/data item.
67 * p: pointer to { pgno_t, u_int32_t }
68 * buf: storage address
72 * RET_ERROR, RET_SUCCESS
75 __ovfl_get(BTREE *t, void *p, size_t *ssz, void **buf, size_t *bufsz)
82 memmove(&pg, p, sizeof(pgno_t));
83 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));
87 if (pg == P_INVALID || sz == 0)
90 /* Make the buffer bigger as necessary. */
92 *buf = (char *)(*buf == NULL ? malloc(sz) : reallocf(*buf, sz));
99 * Step through the linked list of pages, copying the data on each one
100 * into the buffer. Never copy more than the data's length.
102 plen = t->bt_psize - BTDATAOFF;
103 for (p = *buf;; p = (char *)p + nb, pg = h->nextpg) {
104 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
108 memmove(p, (char *)h + BTDATAOFF, nb);
109 mpool_put(t->bt_mp, h, 0);
114 return (RET_SUCCESS);
118 * __OVFL_PUT -- Store an overflow key/data item.
123 * pgno: storage page number
126 * RET_ERROR, RET_SUCCESS
129 __ovfl_put(BTREE *t, const DBT *dbt, pgno_t *pg)
138 * Allocate pages and copy the key/data record into them. Store the
139 * number of the first page in the chain.
141 plen = t->bt_psize - BTDATAOFF;
142 for (last = NULL, p = dbt->data, sz = dbt->size;;
143 p = (char *)p + plen, last = h) {
144 if ((h = __bt_new(t, &npg)) == NULL)
148 h->nextpg = h->prevpg = P_INVALID;
149 h->flags = P_OVERFLOW;
150 h->lower = h->upper = 0;
153 memmove((char *)h + BTDATAOFF, p, nb);
156 last->nextpg = h->pgno;
157 mpool_put(t->bt_mp, last, MPOOL_DIRTY);
161 if ((sz -= nb) == 0) {
162 mpool_put(t->bt_mp, h, MPOOL_DIRTY);
166 return (RET_SUCCESS);
170 * __OVFL_DELETE -- Delete an overflow chain.
174 * p: pointer to { pgno_t, u_int32_t }
177 * RET_ERROR, RET_SUCCESS
180 __ovfl_delete(BTREE *t, void *p)
187 memmove(&pg, p, sizeof(pgno_t));
188 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));
191 if (pg == P_INVALID || sz == 0)
194 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
197 /* Don't delete chains used by internal pages. */
198 if (h->flags & P_PRESERVE) {
199 mpool_put(t->bt_mp, h, 0);
200 return (RET_SUCCESS);
203 /* Step through the chain, calling the free routine for each page. */
204 for (plen = t->bt_psize - BTDATAOFF;; sz -= plen) {
209 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
212 return (RET_SUCCESS);