1PG_RESETWAL(1) PostgreSQL 13.4 Documentation PG_RESETWAL(1)
2
6 pg_resetwal - reset the write-ahead log and other control information
7 of a PostgreSQL database cluster
8
10 pg_resetwal [-f | --force] [-n | --dry-run] [option...] [-D |
11 --pgdata]datadir
12
14 pg_resetwal clears the write-ahead log (WAL) and optionally resets some
15 other control information stored in the pg_control file. This function
16 is sometimes needed if these files have become corrupted. It should be
17 used only as a last resort, when the server will not start due to such
18 corruption.
19 After running this command, it should be possible to start the server,
21 but bear in mind that the database might contain inconsistent data due
22 to partially-committed transactions. You should immediately dump your
23 data, run initdb, and reload. After reload, check for inconsistencies
24 and repair as needed.
25 This utility can only be run by the user who installed the server,
27 because it requires read/write access to the data directory. For safety
28 reasons, you must specify the data directory on the command line.
29 pg_resetwal does not use the environment variable PGDATA.
30 If pg_resetwal complains that it cannot determine valid data for
32 pg_control, you can force it to proceed anyway by specifying the -f
33 (force) option. In this case plausible values will be substituted for
34 the missing data. Most of the fields can be expected to match, but
35 manual assistance might be needed for the next OID, next transaction ID
36 and epoch, next multitransaction ID and offset, and WAL starting
37 location fields. These fields can be set using the options discussed
38 below. If you are not able to determine correct values for all these
39 fields, -f can still be used, but the recovered database must be
40 treated with even more suspicion than usual: an immediate dump and
41 reload is imperative. Do not execute any data-modifying operations in
42 the database before you dump, as any such action is likely to make the
43 corruption worse.
44
46 -f
47 --force
48 Force pg_resetwal to proceed even if it cannot determine valid data
49 for pg_control, as explained above.
50 -n
52 --dry-run
53 The -n/--dry-run option instructs pg_resetwal to print the values
54 reconstructed from pg_control and values about to be changed, and
55 then exit without modifying anything. This is mainly a debugging
56 tool, but can be useful as a sanity check before allowing
57 pg_resetwal to proceed for real.
58 -V
60 --version
61 Display version information, then exit.
62 -?
64 --help
65 Show help, then exit.
66 The following options are only needed when pg_resetwal is unable to
68 determine appropriate values by reading pg_control. Safe values can be
69 determined as described below. For values that take numeric arguments,
70 hexadecimal values can be specified by using the prefix 0x.
71 -c xid,xid
73 --commit-timestamp-ids=xid,xid
74 Manually set the oldest and newest transaction IDs for which the
75 commit time can be retrieved.
76 A safe value for the oldest transaction ID for which the commit
78 time can be retrieved (first part) can be determined by looking for
79 the numerically smallest file name in the directory pg_commit_ts
80 under the data directory. Conversely, a safe value for the newest
81 transaction ID for which the commit time can be retrieved (second
82 part) can be determined by looking for the numerically greatest
83 file name in the same directory. The file names are in hexadecimal.
84 -e xid_epoch
86 --epoch=xid_epoch
87 Manually set the next transaction ID's epoch.
88 The transaction ID epoch is not actually stored anywhere in the
90 database except in the field that is set by pg_resetwal, so any
91 value will work so far as the database itself is concerned. You
92 might need to adjust this value to ensure that replication systems
93 such as Slony-I and Skytools work correctly — if so, an appropriate
94 value should be obtainable from the state of the downstream
95 replicated database.
96 -l walfile
98 --next-wal-file=walfile
99 Manually set the WAL starting location by specifying the name of
100 the next WAL segment file.
101 The name of next WAL segment file should be larger than any WAL
103 segment file name currently existing in the directory pg_wal under
104 the data directory. These names are also in hexadecimal and have
105 three parts. The first part is the “timeline ID” and should usually
106 be kept the same. For example, if 00000001000000320000004A is the
107 largest entry in pg_wal, use -l 00000001000000320000004B or higher.
108 Note that when using nondefault WAL segment sizes, the numbers in
110 the WAL file names are different from the LSNs that are reported by
111 system functions and system views. This option takes a WAL file
112 name, not an LSN.
113 Note
115 pg_resetwal itself looks at the files in pg_wal and chooses a
116 default -l setting beyond the last existing file name.
117 Therefore, manual adjustment of -l should only be needed if you
118 are aware of WAL segment files that are not currently present
119 in pg_wal, such as entries in an offline archive; or if the
120 contents of pg_wal have been lost entirely.
121 -m mxid,mxid
123 --multixact-ids=mxid,mxid
124 Manually set the next and oldest multitransaction ID.
125 A safe value for the next multitransaction ID (first part) can be
127 determined by looking for the numerically largest file name in the
128 directory pg_multixact/offsets under the data directory, adding
129 one, and then multiplying by 65536 (0x10000). Conversely, a safe
130 value for the oldest multitransaction ID (second part of -m) can be
131 determined by looking for the numerically smallest file name in the
132 same directory and multiplying by 65536. The file names are in
133 hexadecimal, so the easiest way to do this is to specify the option
134 value in hexadecimal and append four zeroes.
135 -o oid
137 --next-oid=oid
138 Manually set the next OID.
139 There is no comparably easy way to determine a next OID that's
141 beyond the largest one in the database, but fortunately it is not
142 critical to get the next-OID setting right.
143 -O mxoff
145 --multixact-offset=mxoff
146 Manually set the next multitransaction offset.
147 A safe value can be determined by looking for the numerically
149 largest file name in the directory pg_multixact/members under the
150 data directory, adding one, and then multiplying by 52352 (0xCC80).
151 The file names are in hexadecimal. There is no simple recipe such
152 as the ones for other options of appending zeroes.
153 --wal-segsize=wal_segment_size
155 Set the new WAL segment size, in megabytes. The value must be set
156 to a power of 2 between 1 and 1024 (megabytes). See the same option
157 of initdb(1) for more information.
158 Note
160 While pg_resetwal will set the WAL starting address beyond the
161 latest existing WAL segment file, some segment size changes can
162 cause previous WAL file names to be reused. It is recommended
163 to use -l together with this option to manually set the WAL
164 starting address if WAL file name overlap will cause problems
165 with your archiving strategy.
166 -u xid
168 --oldest-transaction-id=xid
169 Manually set the oldest unfrozen transaction ID.
170 A safe value can be determined by looking for the numerically
172 smallest file name in the directory pg_xact under the data
173 directory and then multiplying by 1048576 (0x100000). Note that the
174 file names are in hexadecimal. It is usually easiest to specify the
175 option value in hexadecimal too. For example, if 0007 is the
176 smallest entry in pg_xact, -u 0x700000 will work (five trailing
177 zeroes provide the proper multiplier).
178 -x xid
180 --next-transaction-id=xid
181 Manually set the next transaction ID.
182 A safe value can be determined by looking for the numerically
184 largest file name in the directory pg_xact under the data
185 directory, adding one, and then multiplying by 1048576 (0x100000).
186 Note that the file names are in hexadecimal. It is usually easiest
187 to specify the option value in hexadecimal too. For example, if
188 0011 is the largest entry in pg_xact, -x 0x1200000 will work (five
189 trailing zeroes provide the proper multiplier).
190
192 PG_COLOR
193 Specifies whether to use color in diagnostic messages. Possible
194 values are always, auto and never.
195
197 This command must not be used when the server is running. pg_resetwal
198 will refuse to start up if it finds a server lock file in the data
199 directory. If the server crashed then a lock file might have been left
200 behind; in that case you can remove the lock file to allow pg_resetwal
201 to run. But before you do so, make doubly certain that there is no
202 server process still alive.
203 pg_resetwal works only with servers of the same major version.
205
207 pg_controldata(1)
208PostgreSQL 13.4 2021 PG_RESETWAL(1)