pg_resetwal(1) PostgreSQL 14.5 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.
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 restore. After restore, 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 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.
OPTIONS
-f
--force
Force pg_resetwal to proceed even if it cannot determine valid data
for pg_control, as explained above.
-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.
-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.
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 14.5 2022 pg_resetwal(1)
postgresql 14.5 - Generated Tue Aug 30 07:51:20 CDT 2022