/*-
 * 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[] = "@(#)log_findckp.c 10.17 (Sleepycat) 9/17/98";
#endif /* not lint */

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

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

#include "db_int.h"
#include "shqueue.h"
#include "log.h"
#include "txn.h"
#include "common_ext.h"

/*
 * __log_findckp --
 *
 * Looks for the most recent checkpoint that occurs before the most recent
 * checkpoint LSN, subject to the constraint that there must be at least two
 * checkpoints.  The reason you need two checkpoints is that you might have
 * crashed during the most recent one and may not have a copy of all the
 * open files.  This is the point from which recovery can start and the
 * point up to which archival/truncation can take place.  Checkpoints in
 * the log look like:
 *
 * -------------------------------------------------------------------
 *  | ckp A, ckplsn 100 |  .... record .... | ckp B, ckplsn 600 | ...
 * -------------------------------------------------------------------
 *         LSN 500                                 LSN 1000
 *
 * If we read what log returns from using the DB_CKP parameter to logput,
 * we'll get the record at LSN 1000.  The checkpoint LSN there is 600.
 * Now we have to scan backwards looking for a checkpoint before LSN 600.
 * We find one at 500.  This means that we can truncate the log before
 * 500 or run recovery beginning at 500.
 *
 * Returns 0 if we find a suitable checkpoint or we retrieved the
 * first record in the log from which to start.
 * Returns DB_NOTFOUND if there are no log records.
 * Returns errno on error.
 *
 * PUBLIC: int __log_findckp __P((DB_LOG *, DB_LSN *));
 */
int
__log_findckp(lp, lsnp)
        DB_LOG *lp;
        DB_LSN *lsnp;
{
        DBT data;
        DB_LSN ckp_lsn, final_ckp, last_ckp, next_lsn;
        __txn_ckp_args *ckp_args;
        int ret, verbose;

        verbose = lp->dbenv != NULL && lp->dbenv->db_verbose != 0;

        /*
         * Need to find the appropriate point from which to begin
         * recovery.
         */
        memset(&data, 0, sizeof(data));
        if (F_ISSET(lp, DB_AM_THREAD))
                F_SET(&data, DB_DBT_MALLOC);
        ZERO_LSN(ckp_lsn);
        if ((ret = log_get(lp, &last_ckp, &data, DB_CHECKPOINT)) != 0)
                if (ret == ENOENT)
                        goto get_first;
                else
                        return (ret);

        final_ckp = last_ckp;
        next_lsn = last_ckp;
        do {
                if (F_ISSET(lp, DB_AM_THREAD))
                        __os_free(data.data, data.size);

                if ((ret = log_get(lp, &next_lsn, &data, DB_SET)) != 0)
                        return (ret);
                if ((ret = __txn_ckp_read(data.data, &ckp_args)) != 0) {
                        if (F_ISSET(lp, DB_AM_THREAD))
                                __os_free(data.data, data.size);
                        return (ret);
                }
                if (IS_ZERO_LSN(ckp_lsn))
                        ckp_lsn = ckp_args->ckp_lsn;
                if (verbose) {
                        __db_err(lp->dbenv, "Checkpoint at: [%lu][%lu]",
                            (u_long)last_ckp.file, (u_long)last_ckp.offset);
                        __db_err(lp->dbenv, "Checkpoint LSN: [%lu][%lu]",
                            (u_long)ckp_args->ckp_lsn.file,
                            (u_long)ckp_args->ckp_lsn.offset);
                        __db_err(lp->dbenv, "Previous checkpoint: [%lu][%lu]",
                            (u_long)ckp_args->last_ckp.file,
                            (u_long)ckp_args->last_ckp.offset);
                }
                last_ckp = next_lsn;
                next_lsn = ckp_args->last_ckp;
                __os_free(ckp_args, sizeof(*ckp_args));

                /*
                 * Keep looping until either you 1) run out of checkpoints,
                 * 2) you've found a checkpoint before the most recent
                 * checkpoint's LSN and you have at least 2 checkpoints.
                 */
        } while (!IS_ZERO_LSN(next_lsn) &&
            (log_compare(&last_ckp, &ckp_lsn) > 0 ||
            log_compare(&final_ckp, &last_ckp) == 0));

        if (F_ISSET(lp, DB_AM_THREAD))
                __os_free(data.data, data.size);

        /*
         * At this point, either, next_lsn is ZERO or ckp_lsn is the
         * checkpoint lsn and last_ckp is the LSN of the last checkpoint
         * before ckp_lsn.  If the compare in the loop is still true, then
         * next_lsn must be 0 and we need to roll forward from the
         * beginning of the log.
         */
        if (log_compare(&last_ckp, &ckp_lsn) > 0 ||
            log_compare(&final_ckp, &last_ckp) == 0) {
get_first:      if ((ret = log_get(lp, &last_ckp, &data, DB_FIRST)) != 0)
                        return (ret);
                if (F_ISSET(lp, DB_AM_THREAD))
                        __os_free(data.data, data.size);
        }
        *lsnp = last_ckp;

        return (IS_ZERO_LSN(last_ckp) ? DB_NOTFOUND : 0);
}