xref: /titanic_44/usr/src/cmd/sendmail/db/log/log_findckp.c (revision 3f7d54a6b84904c8f4d8daa4c7b577bede7df8b9)
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	10.17 (Sleepycat) 9/17/98";
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, subject to the constraint that there must be at least two
32  * checkpoints.  The reason you need two checkpoints is that you might have
33  * crashed during the most recent one and may not have a copy of all the
34  * open files.  This is the point from which recovery can start and the
35  * point up to which archival/truncation can take place.  Checkpoints in
36  * the log look like:
37  *
38  * -------------------------------------------------------------------
39  *  | ckp A, ckplsn 100 |  .... record .... | ckp B, ckplsn 600 | ...
40  * -------------------------------------------------------------------
41  *         LSN 500                                 LSN 1000
42  *
43  * If we read what log returns from using the DB_CKP parameter to logput,
44  * we'll get the record at LSN 1000.  The checkpoint LSN there is 600.
45  * Now we have to scan backwards looking for a checkpoint before LSN 600.
46  * We find one at 500.  This means that we can truncate the log before
47  * 500 or run recovery beginning at 500.
48  *
49  * Returns 0 if we find a suitable checkpoint or we retrieved the
50  * first record in the log from which to start.
51  * Returns DB_NOTFOUND if there are no log records.
52  * Returns errno on error.
53  *
54  * PUBLIC: int __log_findckp __P((DB_LOG *, DB_LSN *));
55  */
56 int
57 __log_findckp(lp, lsnp)
58 	DB_LOG *lp;
59 	DB_LSN *lsnp;
60 {
61 	DBT data;
62 	DB_LSN ckp_lsn, final_ckp, last_ckp, next_lsn;
63 	__txn_ckp_args *ckp_args;
64 	int ret, verbose;
65 
66 	verbose = lp->dbenv != NULL && lp->dbenv->db_verbose != 0;
67 
68 	/*
69 	 * Need to find the appropriate point from which to begin
70 	 * recovery.
71 	 */
72 	memset(&data, 0, sizeof(data));
73 	if (F_ISSET(lp, DB_AM_THREAD))
74 		F_SET(&data, DB_DBT_MALLOC);
75 	ZERO_LSN(ckp_lsn);
76 	if ((ret = log_get(lp, &last_ckp, &data, DB_CHECKPOINT)) != 0)
77 		if (ret == ENOENT)
78 			goto get_first;
79 		else
80 			return (ret);
81 
82 	final_ckp = last_ckp;
83 	next_lsn = last_ckp;
84 	do {
85 		if (F_ISSET(lp, DB_AM_THREAD))
86 			__os_free(data.data, data.size);
87 
88 		if ((ret = log_get(lp, &next_lsn, &data, DB_SET)) != 0)
89 			return (ret);
90 		if ((ret = __txn_ckp_read(data.data, &ckp_args)) != 0) {
91 			if (F_ISSET(lp, DB_AM_THREAD))
92 				__os_free(data.data, data.size);
93 			return (ret);
94 		}
95 		if (IS_ZERO_LSN(ckp_lsn))
96 			ckp_lsn = ckp_args->ckp_lsn;
97 		if (verbose) {
98 			__db_err(lp->dbenv, "Checkpoint at: [%lu][%lu]",
99 			    (u_long)last_ckp.file, (u_long)last_ckp.offset);
100 			__db_err(lp->dbenv, "Checkpoint LSN: [%lu][%lu]",
101 			    (u_long)ckp_args->ckp_lsn.file,
102 			    (u_long)ckp_args->ckp_lsn.offset);
103 			__db_err(lp->dbenv, "Previous checkpoint: [%lu][%lu]",
104 			    (u_long)ckp_args->last_ckp.file,
105 			    (u_long)ckp_args->last_ckp.offset);
106 		}
107 		last_ckp = next_lsn;
108 		next_lsn = ckp_args->last_ckp;
109 		__os_free(ckp_args, sizeof(*ckp_args));
110 
111 		/*
112 		 * Keep looping until either you 1) run out of checkpoints,
113 		 * 2) you've found a checkpoint before the most recent
114 		 * checkpoint's LSN and you have at least 2 checkpoints.
115 		 */
116 	} while (!IS_ZERO_LSN(next_lsn) &&
117 	    (log_compare(&last_ckp, &ckp_lsn) > 0 ||
118 	    log_compare(&final_ckp, &last_ckp) == 0));
119 
120 	if (F_ISSET(lp, DB_AM_THREAD))
121 		__os_free(data.data, data.size);
122 
123 	/*
124 	 * At this point, either, next_lsn is ZERO or ckp_lsn is the
125 	 * checkpoint lsn and last_ckp is the LSN of the last checkpoint
126 	 * before ckp_lsn.  If the compare in the loop is still true, then
127 	 * next_lsn must be 0 and we need to roll forward from the
128 	 * beginning of the log.
129 	 */
130 	if (log_compare(&last_ckp, &ckp_lsn) > 0 ||
131 	    log_compare(&final_ckp, &last_ckp) == 0) {
132 get_first:	if ((ret = log_get(lp, &last_ckp, &data, DB_FIRST)) != 0)
133 			return (ret);
134 		if (F_ISSET(lp, DB_AM_THREAD))
135 			__os_free(data.data, data.size);
136 	}
137 	*lsnp = last_ckp;
138 
139 	return (IS_ZERO_LSN(last_ckp) ? DB_NOTFOUND : 0);
140 }
141