db2/log/log_findckp.c

   1 /*-
   2  * See the file LICENSE for redistribution information.
   3  *
   4  * Copyright (c) 1996, 1997, 1998
   5  *      Sleepycat Software.  All rights reserved.
   6  */
   7
   8 #include "config.h"
   9
  10 #ifndef lint
  11 static const char sccsid[] = "@(#)log_findckp.c 10.15 (Sleepycat) 4/26/98";
  12 #endif /* not lint */
  13
  14 #ifndef NO_SYSTEM_INCLUDES
  15 #include <sys/types.h>
  16
  17 #include <errno.h>
  18 #include <string.h>
  19 #endif
  20
  21 #include "db_int.h"
  22 #include "shqueue.h"
  23 #include "log.h"
  24 #include "txn.h"
  25 #include "common_ext.h"
  26
  27 /*
  28  * __log_findckp --
  29  *
  30  * Looks for the most recent checkpoint that occurs before the most recent
  31  * checkpoint LSN.  This is the point from which recovery can start and the
  32  * point up to which archival/truncation can take place.  Checkpoints in
  33  * the log look like:
  34  *
  35  * -------------------------------------------------------------------
  36  *  | ckp A, ckplsn 100 |  .... record .... | ckp B, ckplsn 600 | ...
  37  * -------------------------------------------------------------------
  38  *         LSN 500                                 LSN 1000
  39  *
  40  * If we read what log returns from using the DB_CKP parameter to logput,
  41  * we'll get the record at LSN 1000.  The checkpoint LSN there is 600.
  42  * Now we have to scan backwards looking for a checkpoint before LSN 600.
  43  * We find one at 500.  This means that we can truncate the log before
  44  * 500 or run recovery beginning at 500.
  45  *
  46  * Returns 0 if we find a suitable checkpoint or we retrieved the
  47  * first record in the log from which to start.
  48  * Returns DB_NOTFOUND if there are no log records.
  49  * Returns errno on error.
  50  *
  51  * PUBLIC: int __log_findckp __P((DB_LOG *, DB_LSN *));
  52  */
  53 int
  54 __log_findckp(lp, lsnp)
  55         DB_LOG *lp;
  56         DB_LSN *lsnp;
  57 {
  58         DBT data;
  59         DB_LSN ckp_lsn, last_ckp, next_lsn;
  60         __txn_ckp_args *ckp_args;
  61         int ret, verbose;
  62
  63         verbose = lp->dbenv != NULL && lp->dbenv->db_verbose != 0;
  64
  65         /*
  66          * Need to find the appropriate point from which to begin
  67          * recovery.
  68          */
  69         memset(&data, 0, sizeof(data));
  70         if (F_ISSET(lp, DB_AM_THREAD))
  71                 F_SET(&data, DB_DBT_MALLOC);
  72         ZERO_LSN(ckp_lsn);
  73         if ((ret = log_get(lp, &last_ckp, &data, DB_CHECKPOINT)) != 0) {
  74                 if (ret == ENOENT)
  75                         goto get_first;
  76                 else
  77                         return (ret);
  78         }
  79
  80         next_lsn = last_ckp;
  81         do {
  82                 if (F_ISSET(lp, DB_AM_THREAD))
  83                         __db_free(data.data);
  84
  85                 if ((ret = log_get(lp, &next_lsn, &data, DB_SET)) != 0)
  86                         return (ret);
  87                 if ((ret = __txn_ckp_read(data.data, &ckp_args)) != 0) {
  88                         if (F_ISSET(lp, DB_AM_THREAD))
  89                                 __db_free(data.data);
  90                         return (ret);
  91                 }
  92                 if (IS_ZERO_LSN(ckp_lsn))
  93                         ckp_lsn = ckp_args->ckp_lsn;
  94                 if (verbose) {
  95                         __db_err(lp->dbenv, "Checkpoint at: [%lu][%lu]",
  96                             (u_long)last_ckp.file, (u_long)last_ckp.offset);
  97                         __db_err(lp->dbenv, "Checkpoint LSN: [%lu][%lu]",
  98                             (u_long)ckp_args->ckp_lsn.file,
  99                             (u_long)ckp_args->ckp_lsn.offset);
 100                         __db_err(lp->dbenv, "Previous checkpoint: [%lu][%lu]",
 101                             (u_long)ckp_args->last_ckp.file,
 102                             (u_long)ckp_args->last_ckp.offset);
 103                 }
 104                 last_ckp = next_lsn;
 105                 next_lsn = ckp_args->last_ckp;
 106                 __db_free(ckp_args);
 107         } while (!IS_ZERO_LSN(next_lsn) &&
 108             log_compare(&last_ckp, &ckp_lsn) > 0);
 109
 110         if (F_ISSET(lp, DB_AM_THREAD))
 111                 __db_free(data.data);
 112
 113         /*
 114          * At this point, either, next_lsn is ZERO or ckp_lsn is the
 115          * checkpoint lsn and last_ckp is the LSN of the last checkpoint
 116          * before ckp_lsn.  If the compare in the loop is still true, then
 117          * next_lsn must be 0 and we need to roll forward from the
 118          * beginning of the log.
 119          */
 120         if (log_compare(&last_ckp, &ckp_lsn) > 0) {
 121 get_first:      if ((ret = log_get(lp, &last_ckp, &data, DB_FIRST)) != 0)
 122                         return (ret);
 123                 if (F_ISSET(lp, DB_AM_THREAD))
 124                         __db_free(data.data);
 125         }
 126         *lsnp = last_ckp;
 127
 128         return (IS_ZERO_LSN(last_ckp) ? DB_NOTFOUND : 0);
 129 }