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36 * @(#)bt_overflow.c 8.5 (Berkeley) 7/16/94
39 #include <sys/param.h>
51 * Big key and data entries are stored on linked lists of pages. The initial
52 * reference is byte string stored with the key or data and is the page number
53 * and size. The actual record is stored in a chain of pages linked by the
54 * nextpg field of the PAGE header.
56 * The first page of the chain has a special property. If the record is used
57 * by an internal page, it cannot be deleted and the P_PRESERVE bit will be set
61 * A single DBT is written to each chain, so a lot of space on the last page
62 * is wasted. This is a fairly major bug for some data sets.
66 * __OVFL_GET -- Get an overflow key/data item.
70 * p: pointer to { pgno_t, u_int32_t }
71 * buf: storage address
75 * RET_ERROR, RET_SUCCESS
78 __ovfl_get(t, p, ssz, buf, bufsz)
90 memmove(&pg, p, sizeof(pgno_t));
91 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));
95 if (pg == P_INVALID || sz == 0)
98 /* Make the buffer bigger as necessary. */
100 *buf = (char *)(*buf == NULL ? malloc(sz) : reallocf(*buf, sz));
107 * Step through the linked list of pages, copying the data on each one
108 * into the buffer. Never copy more than the data's length.
110 plen = t->bt_psize - BTDATAOFF;
111 for (p = *buf;; p = (char *)p + nb, pg = h->nextpg) {
112 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
116 memmove(p, (char *)h + BTDATAOFF, nb);
117 mpool_put(t->bt_mp, h, 0);
122 return (RET_SUCCESS);
126 * __OVFL_PUT -- Store an overflow key/data item.
131 * pgno: storage page number
134 * RET_ERROR, RET_SUCCESS
137 __ovfl_put(t, dbt, pg)
149 * Allocate pages and copy the key/data record into them. Store the
150 * number of the first page in the chain.
152 plen = t->bt_psize - BTDATAOFF;
153 for (last = NULL, p = dbt->data, sz = dbt->size;;
154 p = (char *)p + plen, last = h) {
155 if ((h = __bt_new(t, &npg)) == NULL)
159 h->nextpg = h->prevpg = P_INVALID;
160 h->flags = P_OVERFLOW;
161 h->lower = h->upper = 0;
164 memmove((char *)h + BTDATAOFF, p, nb);
167 last->nextpg = h->pgno;
168 mpool_put(t->bt_mp, last, MPOOL_DIRTY);
172 if ((sz -= nb) == 0) {
173 mpool_put(t->bt_mp, h, MPOOL_DIRTY);
177 return (RET_SUCCESS);
181 * __OVFL_DELETE -- Delete an overflow chain.
185 * p: pointer to { pgno_t, u_int32_t }
188 * RET_ERROR, RET_SUCCESS
200 memmove(&pg, p, sizeof(pgno_t));
201 memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));
204 if (pg == P_INVALID || sz == 0)
207 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
210 /* Don't delete chains used by internal pages. */
211 if (h->flags & P_PRESERVE) {
212 mpool_put(t->bt_mp, h, 0);
213 return (RET_SUCCESS);
216 /* Step through the chain, calling the free routine for each page. */
217 for (plen = t->bt_psize - BTDATAOFF;; sz -= plen) {
222 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
225 return (RET_SUCCESS);