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db_dup.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *    Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)db_dup.c      10.35 (Sleepycat) 12/2/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <errno.h>
#include <string.h>
#endif

#include "db_int.h"
#include "db_page.h"
#include "btree.h"
#include "db_am.h"

static int __db_addpage __P((DBC *,
    PAGE **, db_indx_t *, int (*)(DBC *, u_int32_t, PAGE **)));
static int __db_dsplit __P((DBC *,
    PAGE **, db_indx_t *, u_int32_t, int (*)(DBC *, u_int32_t, PAGE **)));

/*
 * __db_dput --
 *    Put a duplicate item onto a duplicate page at the given index.
 *
 * PUBLIC: int __db_dput __P((DBC *, DBT *,
 * PUBLIC:    PAGE **, db_indx_t *, int (*)(DBC *, u_int32_t, PAGE **)));
 */
int
__db_dput(dbc, dbt, pp, indxp, newfunc)
      DBC *dbc;
      DBT *dbt;
      PAGE **pp;
      db_indx_t *indxp;
      int (*newfunc) __P((DBC *, u_int32_t, PAGE **));
{
      BOVERFLOW bo;
      DBT *data_dbtp, hdr_dbt, *hdr_dbtp;
      PAGE *pagep;
      db_indx_t size, isize;
      db_pgno_t pgno;
      int ret;

      /*
       * We need some access method independent threshold for when we put
       * a duplicate item onto an overflow page.
       */
      if (dbt->size > 0.25 * dbc->dbp->pgsize) {
            if ((ret = __db_poff(dbc, dbt, &pgno, newfunc)) != 0)
                  return (ret);
            UMRW(bo.unused1);
            B_TSET(bo.type, B_OVERFLOW, 0);
            UMRW(bo.unused2);
            bo.tlen = dbt->size;
            bo.pgno = pgno;
            hdr_dbt.data = &bo;
            hdr_dbt.size = isize = BOVERFLOW_SIZE;
            hdr_dbtp = &hdr_dbt;
            size = BOVERFLOW_PSIZE;
            data_dbtp = NULL;
      } else {
            size = BKEYDATA_PSIZE(dbt->size);
            isize = BKEYDATA_SIZE(dbt->size);
            hdr_dbtp = NULL;
            data_dbtp = dbt;
      }

      pagep = *pp;
      if (size > P_FREESPACE(pagep)) {
            if (*indxp == NUM_ENT(*pp) && NEXT_PGNO(*pp) == PGNO_INVALID)
                  ret = __db_addpage(dbc, pp, indxp, newfunc);
            else
                  ret = __db_dsplit(dbc, pp, indxp, isize, newfunc);
            if (ret != 0)
                  /*
                   * XXX
                   * Pages not returned to free list.
                   */
                  return (ret);
            pagep = *pp;
      }

      /*
       * Now, pagep references the page on which to insert and indx is the
       * the location to insert.
       */
      if ((ret = __db_pitem(dbc,
          pagep, (u_int32_t)*indxp, isize, hdr_dbtp, data_dbtp)) != 0)
            return (ret);

      (void)memp_fset(dbc->dbp->mpf, pagep, DB_MPOOL_DIRTY);
      return (0);
}

/*
 * __db_drem --
 *    Remove a duplicate at the given index on the given page.
 *
 * PUBLIC: int __db_drem __P((DBC *,
 * PUBLIC:    PAGE **, u_int32_t, int (*)(DBC *, PAGE *)));
 */
int
__db_drem(dbc, pp, indx, freefunc)
      DBC *dbc;
      PAGE **pp;
      u_int32_t indx;
      int (*freefunc) __P((DBC *, PAGE *));
{
      PAGE *pagep;
      int ret;

      pagep = *pp;

      /* Check if we are freeing a big item. */
      if (B_TYPE(GET_BKEYDATA(pagep, indx)->type) == B_OVERFLOW) {
            if ((ret = __db_doff(dbc,
                GET_BOVERFLOW(pagep, indx)->pgno, freefunc)) != 0)
                  return (ret);
            ret = __db_ditem(dbc, pagep, indx, BOVERFLOW_SIZE);
      } else
            ret = __db_ditem(dbc, pagep, indx,
                BKEYDATA_SIZE(GET_BKEYDATA(pagep, indx)->len));
      if (ret != 0)
            return (ret);

      if (NUM_ENT(pagep) == 0) {
            /*
             * If the page is emptied, then the page is freed and the pp
             * parameter is set to reference the next, locked page in the
             * duplicate chain, if one exists.  If there was no such page,
             * then it is set to NULL.
             *
             * !!!
             * __db_relink will set the dirty bit for us.
             */
            if ((ret = __db_relink(dbc, DB_REM_PAGE, pagep, pp, 0)) != 0)
                  return (ret);
            if ((ret = freefunc(dbc, pagep)) != 0)
                  return (ret);
      } else
            (void)memp_fset(dbc->dbp->mpf, pagep, DB_MPOOL_DIRTY);

      return (0);
}

/*
 * __db_dend --
 *    Find the last page in a set of offpage duplicates.
 *
 * PUBLIC: int __db_dend __P((DBC *, db_pgno_t, PAGE **));
 */
int
__db_dend(dbc, pgno, pp)
      DBC *dbc;
      db_pgno_t pgno;
      PAGE **pp;
{
      DB *dbp;
      PAGE *h;
      int ret;

      dbp = dbc->dbp;

      /*
       * This implements DB_KEYLAST.  The last page is returned in pp; pgno
       * should be the page number of the first page of the duplicate chain.
       *
       * *pp may be non-NULL -- if given a valid page use it.
       */
      if (*pp != NULL)
            goto started;
      for (;;) {
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, pp)) != 0) {
                  (void)__db_pgerr(dbp, pgno);
                  return (ret);
            }
started:    h = *pp;

            if ((pgno = NEXT_PGNO(h)) == PGNO_INVALID)
                  break;

            if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                  return (ret);
      }
      return (0);
}

/*
 * __db_dsplit --
 *    Split a page of duplicates, calculating the split point based
 *    on an element of size "size" being added at "*indxp".
 *    On entry hp contains a pointer to the page-pointer of the original
 *    page.  On exit, it returns a pointer to the page containing "*indxp"
 *    and "indxp" has been modified to reflect the index on the new page
 *    where the element should be added.  The function returns with
 *    the page on which the insert should happen, not yet put.
 */
static int
__db_dsplit(dbc, hp, indxp, size, newfunc)
      DBC *dbc;
      PAGE **hp;
      db_indx_t *indxp;
      u_int32_t size;
      int (*newfunc) __P((DBC *, u_int32_t, PAGE **));
{
      PAGE *h, *np, *tp;
      BKEYDATA *bk;
      DBT page_dbt;
      DB *dbp;
      size_t pgsize;
      db_indx_t halfbytes, i, indx, lastsum, nindex, oindex, s, sum;
      int did_indx, ret, t_ret;

      h = *hp;
      indx = *indxp;
      ret = 0;
      dbp = dbc->dbp;
      pgsize = dbp->pgsize;

      /* Create a temporary page to do compaction onto. */
      if ((ret = __os_malloc(pgsize, NULL, &tp)) != 0)
            return (ret);

      /* Create new page for the split. */
      if ((ret = newfunc(dbc, P_DUPLICATE, &np)) != 0) {
            __os_free(tp, pgsize);
            return (ret);
      }

      P_INIT(np, pgsize, PGNO(np), PGNO(h), NEXT_PGNO(h), 0,
          P_DUPLICATE);
      P_INIT(tp, pgsize, PGNO(h), PREV_PGNO(h), PGNO(np), 0,
          P_DUPLICATE);

      /* Figure out the split point */
      halfbytes = (pgsize - HOFFSET(h)) / 2;
      did_indx = 0;
      for (sum = 0, lastsum = 0, i = 0; i < NUM_ENT(h); i++) {
            if (i == indx) {
                  sum += size;
                  did_indx = 1;
                  if (lastsum < halfbytes && sum >= halfbytes) {
                        /* We've crossed the halfway point. */
                        if ((db_indx_t)(halfbytes - lastsum) <
                            (db_indx_t)(sum - halfbytes)) {
                              *hp = np;
                              *indxp = 0;
                        } else
                              *indxp = i;
                        break;
                  }
                  *indxp = i;
                  lastsum = sum;
            }
            if (B_TYPE(GET_BKEYDATA(h, i)->type) == B_KEYDATA)
                  sum += BKEYDATA_SIZE(GET_BKEYDATA(h, i)->len);
            else
                  sum += BOVERFLOW_SIZE;

            if (lastsum < halfbytes && sum >= halfbytes) {
                  /* We've crossed the halfway point. */
                  if ((db_indx_t)(sum - halfbytes) <
                      (db_indx_t)(halfbytes - lastsum))
                        i++;
                  break;
            }
      }
      /*
       * Check if we have set the return values of the index pointer and
       * page pointer.
       */
      if (!did_indx) {
            *hp = np;
            *indxp = indx - i;
      }

      if (DB_LOGGING(dbc)) {
            page_dbt.size = dbp->pgsize;
            page_dbt.data = h;
            if ((ret = __db_split_log(dbp->dbenv->lg_info,
                dbc->txn, &LSN(h), 0, DB_SPLITOLD, dbp->log_fileid,
                PGNO(h), &page_dbt, &LSN(h))) != 0) {
                  __os_free(tp, pgsize);
                  return (ret);
            }
            LSN(tp) = LSN(h);
      }

      /*
       * If it's a btree, adjust the cursors.
       *
       * i is the index of the first element to move onto the new page.
       */
      if (dbp->type == DB_BTREE)
            __bam_ca_split(dbp, PGNO(h), PGNO(h), PGNO(np), i, 0);

      for (nindex = 0, oindex = i; oindex < NUM_ENT(h); oindex++) {
            bk = GET_BKEYDATA(h, oindex);
            if (B_TYPE(bk->type) == B_KEYDATA)
                  s = BKEYDATA_SIZE(bk->len);
            else
                  s = BOVERFLOW_SIZE;

            np->inp[nindex++] = HOFFSET(np) -= s;
            memcpy((u_int8_t *)np + HOFFSET(np), bk, s);
            NUM_ENT(np)++;
      }

      /*
       * Now do data compaction by copying the remaining stuff onto the
       * temporary page and then copying it back to the real page.
       */
      for (nindex = 0, oindex = 0; oindex < i; oindex++) {
            bk = GET_BKEYDATA(h, oindex);
            if (B_TYPE(bk->type) == B_KEYDATA)
                  s = BKEYDATA_SIZE(bk->len);
            else
                  s = BOVERFLOW_SIZE;

            tp->inp[nindex++] = HOFFSET(tp) -= s;
            memcpy((u_int8_t *)tp + HOFFSET(tp), bk, s);
            NUM_ENT(tp)++;
      }

      /*
       * This page (the temporary) should be only half full, so we do two
       * memcpy's, one for the top of the page and one for the bottom of
       * the page.  This way we avoid copying the middle which should be
       * about half a page.
       */
      memcpy(h, tp, LOFFSET(tp));
      memcpy((u_int8_t *)h + HOFFSET(tp),
          (u_int8_t *)tp + HOFFSET(tp), pgsize - HOFFSET(tp));
      __os_free(tp, pgsize);

      if (DB_LOGGING(dbc)) {
            /*
             * XXX
             * If either of these fails, are we leaving pages pinned?
             * Yes, but it seems like this happens in error case.
             */
            page_dbt.size = pgsize;
            page_dbt.data = h;
            if ((ret = __db_split_log(dbp->dbenv->lg_info,
                dbc->txn, &LSN(h), 0, DB_SPLITNEW, dbp->log_fileid,
                PGNO(h), &page_dbt, &LSN(h))) != 0)
                  return (ret);

            page_dbt.size = pgsize;
            page_dbt.data = np;
            if ((ret = __db_split_log(dbp->dbenv->lg_info,
                dbc->txn, &LSN(np), 0, DB_SPLITNEW, dbp->log_fileid,
                PGNO(np),  &page_dbt, &LSN(np))) != 0)
                  return (ret);
      }

      /*
       * Finally, if there was a next page after the page being
       * split, fix its prev pointer.
       */
      if (np->next_pgno != PGNO_INVALID)
          ret = __db_relink(dbc, DB_ADD_PAGE, np, NULL, 1);

      /*
       * Figure out if the location we're interested in is on the new
       * page, and if so, reset the callers' pointer.  Push the other
       * page back to the store.
       */
      if (*hp == h)
            t_ret = memp_fput(dbp->mpf, np, DB_MPOOL_DIRTY);
      else
            t_ret = memp_fput(dbp->mpf, h, DB_MPOOL_DIRTY);

      return (ret != 0 ? ret : t_ret);
}

/*
 * __db_ditem --
 *    Remove an item from a page.
 *
 * PUBLIC:  int __db_ditem __P((DBC *, PAGE *, u_int32_t, u_int32_t));
 */
int
__db_ditem(dbc, pagep, indx, nbytes)
      DBC *dbc;
      PAGE *pagep;
      u_int32_t indx, nbytes;
{
      DB *dbp;
      DBT ldbt;
      db_indx_t cnt, offset;
      int ret;
      u_int8_t *from;

      dbp = dbc->dbp;
      if (DB_LOGGING(dbc)) {
            ldbt.data = P_ENTRY(pagep, indx);
            ldbt.size = nbytes;
            if ((ret = __db_addrem_log(dbp->dbenv->lg_info, dbc->txn,
                &LSN(pagep), 0, DB_REM_DUP, dbp->log_fileid, PGNO(pagep),
                (u_int32_t)indx, nbytes, &ldbt, NULL, &LSN(pagep))) != 0)
                  return (ret);
      }

      /*
       * If there's only a single item on the page, we don't have to
       * work hard.
       */
      if (NUM_ENT(pagep) == 1) {
            NUM_ENT(pagep) = 0;
            HOFFSET(pagep) = dbp->pgsize;
            return (0);
      }

      /*
       * Pack the remaining key/data items at the end of the page.  Use
       * memmove(3), the regions may overlap.
       */
      from = (u_int8_t *)pagep + HOFFSET(pagep);
      memmove(from + nbytes, from, pagep->inp[indx] - HOFFSET(pagep));
      HOFFSET(pagep) += nbytes;

      /* Adjust the indices' offsets. */
      offset = pagep->inp[indx];
      for (cnt = 0; cnt < NUM_ENT(pagep); ++cnt)
            if (pagep->inp[cnt] < offset)
                  pagep->inp[cnt] += nbytes;

      /* Shift the indices down. */
      --NUM_ENT(pagep);
      if (indx != NUM_ENT(pagep))
            memmove(&pagep->inp[indx], &pagep->inp[indx + 1],
                sizeof(db_indx_t) * (NUM_ENT(pagep) - indx));

      /* If it's a btree, adjust the cursors. */
      if (dbp->type == DB_BTREE)
            __bam_ca_di(dbp, PGNO(pagep), indx, -1);

      return (0);
}

/*
 * __db_pitem --
 *    Put an item on a page.
 *
 * PUBLIC: int __db_pitem
 * PUBLIC:     __P((DBC *, PAGE *, u_int32_t, u_int32_t, DBT *, DBT *));
 */
int
__db_pitem(dbc, pagep, indx, nbytes, hdr, data)
      DBC *dbc;
      PAGE *pagep;
      u_int32_t indx;
      u_int32_t nbytes;
      DBT *hdr, *data;
{
      DB *dbp;
      BKEYDATA bk;
      DBT thdr;
      int ret;
      u_int8_t *p;

      /*
       * Put a single item onto a page.  The logic figuring out where to
       * insert and whether it fits is handled in the caller.  All we do
       * here is manage the page shuffling.  We cheat a little bit in that
       * we don't want to copy the dbt on a normal put twice.  If hdr is
       * NULL, we create a BKEYDATA structure on the page, otherwise, just
       * copy the caller's information onto the page.
       *
       * This routine is also used to put entries onto the page where the
       * entry is pre-built, e.g., during recovery.  In this case, the hdr
       * will point to the entry, and the data argument will be NULL.
       *
       * !!!
       * There's a tremendous potential for off-by-one errors here, since
       * the passed in header sizes must be adjusted for the structure's
       * placeholder for the trailing variable-length data field.
       */
      dbp = dbc->dbp;
      if (DB_LOGGING(dbc))
            if ((ret = __db_addrem_log(dbp->dbenv->lg_info, dbc->txn,
                &LSN(pagep), 0, DB_ADD_DUP, dbp->log_fileid, PGNO(pagep),
                (u_int32_t)indx, nbytes, hdr, data, &LSN(pagep))) != 0)
                  return (ret);

      if (hdr == NULL) {
            B_TSET(bk.type, B_KEYDATA, 0);
            bk.len = data == NULL ? 0 : data->size;

            thdr.data = &bk;
            thdr.size = SSZA(BKEYDATA, data);
            hdr = &thdr;
      }

      /* Adjust the index table, then put the item on the page. */
      if (indx != NUM_ENT(pagep))
            memmove(&pagep->inp[indx + 1], &pagep->inp[indx],
                sizeof(db_indx_t) * (NUM_ENT(pagep) - indx));
      HOFFSET(pagep) -= nbytes;
      pagep->inp[indx] = HOFFSET(pagep);
      ++NUM_ENT(pagep);

      p = P_ENTRY(pagep, indx);
      memcpy(p, hdr->data, hdr->size);
      if (data != NULL)
            memcpy(p + hdr->size, data->data, data->size);

      /* If it's a btree, adjust the cursors. */
      if (dbp->type == DB_BTREE)
            __bam_ca_di(dbp, PGNO(pagep), indx, 1);

      return (0);
}

/*
 * __db_relink --
 *    Relink around a deleted page.
 *
 * PUBLIC: int __db_relink __P((DBC *, u_int32_t, PAGE *, PAGE **, int));
 */
int
__db_relink(dbc, add_rem, pagep, new_next, needlock)
      DBC *dbc;
      u_int32_t add_rem;
      PAGE *pagep, **new_next;
      int needlock;
{
      DB *dbp;
      PAGE *np, *pp;
      DB_LOCK npl, ppl;
      DB_LSN *nlsnp, *plsnp;
      int ret;

      ret = 0;
      np = pp = NULL;
      npl = ppl = LOCK_INVALID;
      nlsnp = plsnp = NULL;
      dbp = dbc->dbp;

      /*
       * Retrieve and lock the one/two pages.  For a remove, we may need
       * two pages (the before and after).  For an add, we only need one
       * because, the split took care of the prev.
       */
      if (pagep->next_pgno != PGNO_INVALID) {
            if (needlock && (ret = __bam_lget(dbc,
                0, pagep->next_pgno, DB_LOCK_WRITE, &npl)) != 0)
                  goto err;
            if ((ret = memp_fget(dbp->mpf,
                &pagep->next_pgno, 0, &np)) != 0) {
                  (void)__db_pgerr(dbp, pagep->next_pgno);
                  goto err;
            }
            nlsnp = &np->lsn;
      }
      if (add_rem == DB_REM_PAGE && pagep->prev_pgno != PGNO_INVALID) {
            if (needlock && (ret = __bam_lget(dbc,
                0, pagep->prev_pgno, DB_LOCK_WRITE, &ppl)) != 0)
                  goto err;
            if ((ret = memp_fget(dbp->mpf,
                &pagep->prev_pgno, 0, &pp)) != 0) {
                  (void)__db_pgerr(dbp, pagep->next_pgno);
                  goto err;
            }
            plsnp = &pp->lsn;
      }

      /* Log the change. */
      if (DB_LOGGING(dbc)) {
            if ((ret = __db_relink_log(dbp->dbenv->lg_info, dbc->txn,
                &pagep->lsn, 0, add_rem, dbp->log_fileid,
                pagep->pgno, &pagep->lsn,
                pagep->prev_pgno, plsnp, pagep->next_pgno, nlsnp)) != 0)
                  goto err;
            if (np != NULL)
                  np->lsn = pagep->lsn;
            if (pp != NULL)
                  pp->lsn = pagep->lsn;
      }

      /*
       * Modify and release the two pages.
       *
       * !!!
       * The parameter new_next gets set to the page following the page we
       * are removing.  If there is no following page, then new_next gets
       * set to NULL.
       */
      if (np != NULL) {
            if (add_rem == DB_ADD_PAGE)
                  np->prev_pgno = pagep->pgno;
            else
                  np->prev_pgno = pagep->prev_pgno;
            if (new_next == NULL)
                  ret = memp_fput(dbp->mpf, np, DB_MPOOL_DIRTY);
            else {
                  *new_next = np;
                  ret = memp_fset(dbp->mpf, np, DB_MPOOL_DIRTY);
            }
            if (ret != 0)
                  goto err;
            if (needlock)
                  (void)__bam_lput(dbc, npl);
      } else if (new_next != NULL)
            *new_next = NULL;

      if (pp != NULL) {
            pp->next_pgno = pagep->next_pgno;
            if ((ret = memp_fput(dbp->mpf, pp, DB_MPOOL_DIRTY)) != 0)
                  goto err;
            if (needlock)
                  (void)__bam_lput(dbc, ppl);
      }
      return (0);

err:  if (np != NULL)
            (void)memp_fput(dbp->mpf, np, 0);
      if (needlock && npl != LOCK_INVALID)
            (void)__bam_lput(dbc, npl);
      if (pp != NULL)
            (void)memp_fput(dbp->mpf, pp, 0);
      if (needlock && ppl != LOCK_INVALID)
            (void)__bam_lput(dbc, ppl);
      return (ret);
}

/*
 * __db_ddup --
 *    Delete an offpage chain of duplicates.
 *
 * PUBLIC: int __db_ddup __P((DBC *, db_pgno_t, int (*)(DBC *, PAGE *)));
 */
int
__db_ddup(dbc, pgno, freefunc)
      DBC *dbc;
      db_pgno_t pgno;
      int (*freefunc) __P((DBC *, PAGE *));
{
      DB *dbp;
      PAGE *pagep;
      DBT tmp_dbt;
      int ret;

      dbp = dbc->dbp;
      do {
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, &pagep)) != 0) {
                  (void)__db_pgerr(dbp, pgno);
                  return (ret);
            }

            if (DB_LOGGING(dbc)) {
                  tmp_dbt.data = pagep;
                  tmp_dbt.size = dbp->pgsize;
                  if ((ret = __db_split_log(dbp->dbenv->lg_info,
                      dbc->txn, &LSN(pagep), 0, DB_SPLITOLD,
                      dbp->log_fileid, PGNO(pagep), &tmp_dbt,
                      &LSN(pagep))) != 0)
                        return (ret);
            }
            pgno = pagep->next_pgno;
            if ((ret = freefunc(dbc, pagep)) != 0)
                  return (ret);
      } while (pgno != PGNO_INVALID);

      return (0);
}

/*
 * __db_addpage --
 *    Create a new page and link it onto the next_pgno field of the
 *    current page.
 */
static int
__db_addpage(dbc, hp, indxp, newfunc)
      DBC *dbc;
      PAGE **hp;
      db_indx_t *indxp;
      int (*newfunc) __P((DBC *, u_int32_t, PAGE **));
{
      DB *dbp;
      PAGE *newpage;
      int ret;

      dbp = dbc->dbp;
      if ((ret = newfunc(dbc, P_DUPLICATE, &newpage)) != 0)
            return (ret);

      if (DB_LOGGING(dbc)) {
            if ((ret = __db_addpage_log(dbp->dbenv->lg_info,
                dbc->txn, &LSN(*hp), 0, dbp->log_fileid,
                PGNO(*hp), &LSN(*hp), PGNO(newpage), &LSN(newpage))) != 0) {
                  return (ret);
            }
            LSN(newpage) = LSN(*hp);
      }

      PREV_PGNO(newpage) = PGNO(*hp);
      NEXT_PGNO(*hp) = PGNO(newpage);

      if ((ret = memp_fput(dbp->mpf, *hp, DB_MPOOL_DIRTY)) != 0)
            return (ret);
      *hp = newpage;
      *indxp = 0;
      return (0);
}

/*
 * __db_dsearch --
 *    Search a set of duplicates for the proper position for a new duplicate.
 *
 *    + pgno is the page number of the page on which to begin searching.
 *      Since we can continue duplicate searches, it might not be the first
 *      page.
 *
 *    + If we are continuing a search, then *pp may be non-NULL in which
 *      case we do not have to retrieve the page.
 *
 *    + If we are continuing a search, then *indxp contains the first
 *      on pgno of where we should begin the search.
 *
 *    NOTE: if there is no comparison function, then continuing is
 *    meaningless, and *pp should always be NULL and *indxp will be
 *    ignored.
 *
 *    3 return values::
 *
 *    + pp is the returned page pointer of where this element should go.
 *    + indxp is the returned index on that page
 *    + cmpp is the returned final comparison result.
 *
 * PUBLIC: int __db_dsearch __P((DBC *,
 * PUBLIC:     int, DBT *, db_pgno_t, db_indx_t *, PAGE **, int *));
 */
int
__db_dsearch(dbc, is_insert, dbt, pgno, indxp, pp, cmpp)
      DBC *dbc;
      int is_insert, *cmpp;
      DBT *dbt;
      db_pgno_t pgno;
      db_indx_t *indxp;
      PAGE **pp;
{
      DB *dbp;
      PAGE *h;
      db_indx_t base, indx, lim, save_indx;
      db_pgno_t save_pgno;
      int ret;

      dbp = dbc->dbp;

      if (dbp->dup_compare == NULL) {
            /*
             * We may have been given a valid page, but we may not be
             * able to use it.  The problem is that the application is
             * doing a join and we're trying to continue the search,
             * but since the items aren't sorted, we can't.  Discard
             * the page if it's not the one we're going to start with
             * anyway.
             */
            if (*pp != NULL && (*pp)->pgno != pgno) {
                  if ((ret = memp_fput(dbp->mpf, *pp, 0)) != 0)
                        return (ret);
                  *pp = NULL;
            }

            /*
             * If no duplicate function is specified, just go to the end
             * of the duplicate set.
             */
            if (is_insert) {
                  if ((ret = __db_dend(dbc, pgno, pp)) != 0)
                        return (ret);
                  *indxp = NUM_ENT(*pp);
                  return (0);
            }

            /*
             * We are looking for a specific duplicate, so do a linear
             * search.
             */
            if (*pp != NULL)
                  goto nocmp_started;
            for (;;) {
                  if ((ret = memp_fget(dbp->mpf, &pgno, 0, pp)) != 0)
                        goto pg_err;
nocmp_started:          h = *pp;

                  for (*indxp = 0; *indxp < NUM_ENT(h); ++*indxp) {
                        if ((*cmpp = __bam_cmp(dbp,
                            dbt, h, *indxp, __bam_defcmp)) != 0)
                              continue;
                        /*
                         * The duplicate may have already been deleted,
                         * if it's a btree page, in which case we skip
                         * it.
                         */
                        if (dbp->type == DB_BTREE &&
                            B_DISSET(GET_BKEYDATA(h, *indxp)->type))
                              continue;

                        return (0);
                  }

                  if ((pgno = h->next_pgno) == PGNO_INVALID)
                        break;

                  if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                        return (ret);
            }
            *cmpp = 1;              /* We didn't succeed... */
            return (0);
      }

      /*
       * We have a comparison routine, i.e., the duplicates are sorted.
       * Walk through the chain of duplicates, checking the last entry
       * on each page to decide if it's the page we want to search.
       *
       * *pp may be non-NULL -- if we were given a valid page (e.g., are
       * in mid-search), then use the provided page.
       */
      if (*pp != NULL)
            goto cmp_started;
      for (;;) {
            if ((ret = memp_fget(dbp->mpf, &pgno, 0, pp)) != 0)
                  goto pg_err;
cmp_started:      h = *pp;

            if ((pgno = h->next_pgno) == PGNO_INVALID || __bam_cmp(dbp,
                dbt, h, h->entries - 1, dbp->dup_compare) <= 0)
                  break;
            /*
             * Even when continuing a search, make sure we don't skip
             * entries on a new page
             */
            *indxp = 0;

            if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                  return (ret);
      }

      /* Next, do a binary search on the page. */
      base = F_ISSET(dbc, DBC_CONTINUE) ? *indxp : 0;
      for (lim = NUM_ENT(h) - base; lim != 0; lim >>= 1) {
            indx = base + (lim >> 1);
            if ((*cmpp = __bam_cmp(dbp,
                dbt, h, indx, dbp->dup_compare)) == 0) {
                  *indxp = indx;

                  if (dbp->type != DB_BTREE ||
                      !B_DISSET(GET_BKEYDATA(h, *indxp)->type))
                        return (0);
                  goto check_delete;
            }
            if (*cmpp > 0) {
                  base = indx + 1;
                  lim--;
            }
      }

      /*
       * Base references the smallest index larger than the supplied DBT's
       * data item, potentially both 0 and NUM_ENT.
       */
      *indxp = base;
      return (0);

check_delete:
      /*
       * The duplicate may have already been deleted, if it's a btree page,
       * in which case we wander around, hoping to find an entry that hasn't
       * been deleted.  First, wander in a forwardly direction.
       */
      save_pgno = (*pp)->pgno;
      save_indx = *indxp;
      for (++*indxp;;) {
            for (; *indxp < NUM_ENT(h); ++*indxp) {
                  if ((*cmpp = __bam_cmp(dbp,
                      dbt, h, *indxp, dbp->dup_compare)) != 0)
                        goto check_delete_rev;

                  if (!B_DISSET(GET_BKEYDATA(h, *indxp)->type))
                        return (0);
            }
            if ((pgno = h->next_pgno) == PGNO_INVALID)
                  break;

            if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                  return (ret);

            if ((ret = memp_fget(dbp->mpf, &pgno, 0, pp)) != 0)
                  goto pg_err;
            h = *pp;

            *indxp = 0;
      }

check_delete_rev:
      /* Go back to where we started, and wander in a backwardly direction. */
      if (h->pgno != save_pgno) {
            if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                  return (ret);
            if ((ret = memp_fget(dbp->mpf, &save_pgno, 0, pp)) != 0)
                  goto pg_err;
            h = *pp;
      }

      for (;;) {
            while (*indxp > 0) {
                  --*indxp;
                  if ((*cmpp = __bam_cmp(dbp,
                      dbt, h, *indxp, dbp->dup_compare)) != 0)
                        goto check_delete_fail;

                  if (!B_DISSET(GET_BKEYDATA(h, *indxp)->type))
                        return (0);
            }
            if ((pgno = h->prev_pgno) == PGNO_INVALID)
                  break;

            if ((ret = memp_fput(dbp->mpf, h, 0)) != 0)
                  return (ret);

            if ((ret = memp_fget(dbp->mpf, &pgno, 0, pp)) != 0)
                  goto pg_err;
            h = *pp;

            *indxp = NUM_ENT(h);
      }

check_delete_fail:
      *cmpp = 1;              /* We didn't succeed... */
      return (0);

pg_err:     __db_pgerr(dbp, pgno);
      return (ret);
}

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