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pg_resetwal(1)           PostgreSQL 17.4 Documentation          pg_resetwal(1)


NAME

       pg_resetwal - reset the write-ahead log and other control information
       of a PostgreSQL database cluster


SYNOPSIS

       pg_resetwal [-f | --force] [-n | --dry-run] [option...] [-D |
                   --pgdata]datadir


DESCRIPTION

       pg_resetwal clears the write-ahead log (WAL) and optionally resets some
       other control information stored in the pg_control file. This function
       is sometimes needed if these files have become corrupted. It should be
       used only as a last resort, when the server will not start due to such
       corruption.

       Some options, such as --wal-segsize (see below), can also be used to
       modify certain global settings of a database cluster without the need
       to rerun initdb. This can be done safely on an otherwise sound database
       cluster, if none of the dangerous modes mentioned below are used.

       If pg_resetwal is used on a data directory where the server has been
       cleanly shut down and the control file is sound, then it will have no
       effect on the contents of the database system, except that no longer
       used WAL files are cleared away. Any other use is potentially dangerous
       and must be done with great care.  pg_resetwal will require the -f
       (force) option to be specified before working on a data directory in an
       unclean shutdown state or with a corrupted control file.

       After running this command on a data directory with corrupted WAL or a
       corrupted control file, it should be possible to start the server, but
       bear in mind that the database might contain inconsistent data due to
       partially-committed transactions. You should immediately dump your
       data, run initdb, and restore. After restore, check for inconsistencies
       and repair as needed.

       If pg_resetwal complains that it cannot determine valid data for
       pg_control, you can force it to proceed anyway by specifying the -f
       (force) option. In this case plausible values will be substituted for
       the missing data. Most of the fields can be expected to match, but
       manual assistance might be needed for the next OID, next transaction ID
       and epoch, next multitransaction ID and offset, and WAL starting
       location fields. These fields can be set using the options discussed
       below. If you are not able to determine correct values for all these
       fields, -f can still be used, but the recovered database must be
       treated with even more suspicion than usual: an immediate dump and
       restore is imperative.  Do not execute any data-modifying operations in
       the database before you dump, as any such action is likely to make the
       corruption worse.

       This utility can only be run by the user who installed the server,
       because it requires read/write access to the data directory.


OPTIONS

       datadir
       -D datadir
       --pgdata=datadir
           Specifies the location of the database directory. For safety
           reasons, you must specify the data directory on the command line.
           pg_resetwal does not use the environment variable PGDATA.

       -f
       --force
           Force pg_resetwal to proceed even in situations where it could be
           dangerous, as explained above. Specifically, this option is
           required to proceed if the server had not been cleanly shut down or
           if pg_resetwal cannot determine valid data for pg_control.

       -n
       --dry-run
           The -n/--dry-run option instructs pg_resetwal to print the values
           reconstructed from pg_control and values about to be changed, and
           then exit without modifying anything. This is mainly a debugging
           tool, but can be useful as a sanity check before allowing
           pg_resetwal to proceed for real.

       -V
       --version
           Display version information, then exit.

       -?
       --help
           Show help, then exit.

       The following options are only needed when pg_resetwal is unable to
       determine appropriate values by reading pg_control. Safe values can be
       determined as described below. For values that take numeric arguments,
       hexadecimal values can be specified by using the prefix 0x. Note that
       these instructions only apply with the standard block size of 8 kB.

       -c xid,xid
       --commit-timestamp-ids=xid,xid
           Manually set the oldest and newest transaction IDs for which the
           commit time can be retrieved.

           A safe value for the oldest transaction ID for which the commit
           time can be retrieved (first part) can be determined by looking for
           the numerically smallest file name in the directory pg_commit_ts
           under the data directory. Conversely, a safe value for the newest
           transaction ID for which the commit time can be retrieved (second
           part) can be determined by looking for the numerically greatest
           file name in the same directory. The file names are in hexadecimal.

       -e xid_epoch
       --epoch=xid_epoch
           Manually set the next transaction ID's epoch.

           The transaction ID epoch is not actually stored anywhere in the
           database except in the field that is set by pg_resetwal, so any
           value will work so far as the database itself is concerned. You
           might need to adjust this value to ensure that replication systems
           such as Slony-I and Skytools work correctly -- if so, an
           appropriate value should be obtainable from the state of the
           downstream replicated database.

       -l walfile
       --next-wal-file=walfile
           Manually set the WAL starting location by specifying the name of
           the next WAL segment file.

           The name of next WAL segment file should be larger than any WAL
           segment file name currently existing in the directory pg_wal under
           the data directory. These names are also in hexadecimal and have
           three parts. The first part is the "timeline ID" and should usually
           be kept the same. For example, if 00000001000000320000004A is the
           largest entry in pg_wal, use -l 00000001000000320000004B or higher.

           Note that when using nondefault WAL segment sizes, the numbers in
           the WAL file names are different from the LSNs that are reported by
           system functions and system views. This option takes a WAL file
           name, not an LSN.

               Note
               pg_resetwal itself looks at the files in pg_wal and chooses a
               default -l setting beyond the last existing file name.
               Therefore, manual adjustment of -l should only be needed if you
               are aware of WAL segment files that are not currently present
               in pg_wal, such as entries in an offline archive; or if the
               contents of pg_wal have been lost entirely.

       -m mxid,mxid
       --multixact-ids=mxid,mxid
           Manually set the next and oldest multitransaction ID.

           A safe value for the next multitransaction ID (first part) can be
           determined by looking for the numerically largest file name in the
           directory pg_multixact/offsets under the data directory, adding
           one, and then multiplying by 65536 (0x10000). Conversely, a safe
           value for the oldest multitransaction ID (second part of -m) can be
           determined by looking for the numerically smallest file name in the
           same directory and multiplying by 65536. The file names are in
           hexadecimal, so the easiest way to do this is to specify the option
           value in hexadecimal and append four zeroes.

       -o oid
       --next-oid=oid
           Manually set the next OID.

           There is no comparably easy way to determine a next OID that's
           beyond the largest one in the database, but fortunately it is not
           critical to get the next-OID setting right.

       -O mxoff
       --multixact-offset=mxoff
           Manually set the next multitransaction offset.

           A safe value can be determined by looking for the numerically
           largest file name in the directory pg_multixact/members under the
           data directory, adding one, and then multiplying by 52352 (0xCC80).
           The file names are in hexadecimal. There is no simple recipe such
           as the ones for other options of appending zeroes.

       --wal-segsize=wal_segment_size
           Set the new WAL segment size, in megabytes. The value must be set
           to a power of 2 between 1 and 1024 (megabytes). See the same option
           of initdb(1) for more information.

           This option can also be used to change the WAL segment size of an
           existing database cluster, avoiding the need to re-initdb.

               Note
               While pg_resetwal will set the WAL starting address beyond the
               latest existing WAL segment file, some segment size changes can
               cause previous WAL file names to be reused. It is recommended
               to use -l together with this option to manually set the WAL
               starting address if WAL file name overlap will cause problems
               with your archiving strategy.

       -u xid
       --oldest-transaction-id=xid
           Manually set the oldest unfrozen transaction ID.

           A safe value can be determined by looking for the numerically
           smallest file name in the directory pg_xact under the data
           directory and then multiplying by 1048576 (0x100000). Note that the
           file names are in hexadecimal. It is usually easiest to specify the
           option value in hexadecimal too. For example, if 0007 is the
           smallest entry in pg_xact, -u 0x700000 will work (five trailing
           zeroes provide the proper multiplier).

       -x xid
       --next-transaction-id=xid
           Manually set the next transaction ID.

           A safe value can be determined by looking for the numerically
           largest file name in the directory pg_xact under the data
           directory, adding one, and then multiplying by 1048576 (0x100000).
           Note that the file names are in hexadecimal. It is usually easiest
           to specify the option value in hexadecimal too. For example, if
           0011 is the largest entry in pg_xact, -x 0x1200000 will work (five
           trailing zeroes provide the proper multiplier).


ENVIRONMENT

       PG_COLOR
           Specifies whether to use color in diagnostic messages. Possible
           values are always, auto and never.


NOTES

       This command must not be used when the server is running.  pg_resetwal
       will refuse to start up if it finds a server lock file in the data
       directory. If the server crashed then a lock file might have been left
       behind; in that case you can remove the lock file to allow pg_resetwal
       to run. But before you do so, make doubly certain that there is no
       server process still alive.

       pg_resetwal works only with servers of the same major version.


SEE ALSO

       pg_controldata(1)

PostgreSQL 17.4                      2025                       pg_resetwal(1)

postgresql 17.4 - Generated Sat Mar 22 11:49:59 CDT 2025
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