1PG_RESETXLOG(1) PostgreSQL 9.2.24 Documentation PG_RESETXLOG(1)
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6 pg_resetxlog - reset the write-ahead log and other control information
7 of a PostgreSQL database cluster
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10 pg_resetxlog [-f] [-n] [-o oid] [-x xid] [-e xid_epoch] [-m mxid]
11 [-O mxoff] [-l timelineid,fileid,seg] datadir
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14 pg_resetxlog clears the write-ahead log (WAL) and optionally resets
15 some other control information stored in the pg_control file. This
16 function is sometimes needed if these files have become corrupted. It
17 should be used only as a last resort, when the server will not start
18 due to such 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_resetxlog does not use the environment variable PGDATA.
30 If pg_resetxlog 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 address 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 The -o, -x, -e, -m, -O, and -l options allow the next OID, next
46 transaction ID, next transaction ID's epoch, next multitransaction ID,
47 next multitransaction offset, and WAL starting address values to be set
48 manually. These are only needed when pg_resetxlog is unable to
49 determine appropriate values by reading pg_control. Safe values can be
50 determined as follows:
51 · A safe value for the next transaction ID (-x) can be determined by
53 looking for the numerically largest file name in the directory
54 pg_clog under the data directory, adding one, and then multiplying
55 by 1048576. Note that the file names are in hexadecimal. It is
56 usually easiest to specify the option value in hexadecimal too. For
57 example, if 0011 is the largest entry in pg_clog, -x 0x1200000 will
58 work (five trailing zeroes provide the proper multiplier).
59 · A safe value for the next multitransaction ID (-m) can be
61 determined by looking for the numerically largest file name in the
62 directory pg_multixact/offsets under the data directory, adding
63 one, and then multiplying by 65536. As above, the file names are in
64 hexadecimal, so the easiest way to do this is to specify the option
65 value in hexadecimal and add four zeroes.
66 · A safe value for the next multitransaction offset (-O) can be
68 determined by looking for the numerically largest file name in the
69 directory pg_multixact/members under the data directory, adding
70 one, and then multiplying by 65536. As above, the file names are in
71 hexadecimal, so the easiest way to do this is to specify the option
72 value in hexadecimal and add four zeroes.
73 · The WAL starting address (-l) should be larger than any WAL segment
75 file name currently existing in the directory pg_xlog under the
76 data directory. These names are also in hexadecimal and have three
77 parts. The first part is the “timeline ID” and should usually be
78 kept the same. Do not choose a value larger than 255 (0xFF) for the
79 third part; instead increment the second part and reset the third
80 part to 0. For example, if 00000001000000320000004A is the largest
81 entry in pg_xlog, -l 0x1,0x32,0x4B will work; but if the largest
82 entry is 000000010000003A000000FF, choose -l 0x1,0x3B,0x0 or more.
83 Note
85 pg_resetxlog itself looks at the files in pg_xlog and chooses a
86 default -l setting beyond the last existing file name.
87 Therefore, manual adjustment of -l should only be needed if you
88 are aware of WAL segment files that are not currently present
89 in pg_xlog, such as entries in an offline archive; or if the
90 contents of pg_xlog have been lost entirely.
91 · There is no comparably easy way to determine a next OID that's
93 beyond the largest one in the database, but fortunately it is not
94 critical to get the next-OID setting right.
95 · The transaction ID epoch is not actually stored anywhere in the
97 database except in the field that is set by pg_resetxlog, so any
98 value will work so far as the database itself is concerned. You
99 might need to adjust this value to ensure that replication systems
100 such as Slony-I work correctly — if so, an appropriate value should
101 be obtainable from the state of the downstream replicated database.
102 The -n (no operation) option instructs pg_resetxlog to print the values
104 reconstructed from pg_control and then exit without modifying anything.
105 This is mainly a debugging tool, but can be useful as a sanity check
106 before allowing pg_resetxlog to proceed for real.
107 The -V and --version options print the pg_resetxlog version and exit.
109 The options -? and --help show supported arguments, and exit.
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112 This command must not be used when the server is running. pg_resetxlog
113 will refuse to start up if it finds a server lock file in the data
114 directory. If the server crashed then a lock file might have been left
115 behind; in that case you can remove the lock file to allow pg_resetxlog
116 to run. But before you do so, make doubly certain that there is no
117 server process still alive.
118 pg_resetxlog works only with servers of the same major version.
120PostgreSQL 9.2.24 2017-11-06 PG_RESETXLOG(1)