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PG_RESETWAL(1)		 PostgreSQL 17.5 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 17.5			     2025			PG_RESETWAL(1)

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