NAME

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

SYNOPSIS

       pg_resetwal [-f] [-n] [option...] {[-D] 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.

       After running this command, 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 reload. After reload, check for
       inconsistencies and repair as needed.

       This utility can only be run by the user who installed the server, because it requires
       read/write access to the data directory. For safety reasons, you must specify the data
       directory on the command line.  pg_resetwal does not use the environment variable PGDATA.

       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 address 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 reload 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.

OPTIONS

       -f
           Force pg_resetwal to proceed even if it cannot determine valid data for pg_control, as
           explained above.

       -n
           The -n (no operation) 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.

       -c 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
           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
           Manually set the WAL starting address.

           The WAL starting address 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
               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
           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
           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
           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.

       -u 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
           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).

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)