pg_waldump(1) PostgreSQL 17.4 Documentation pg_waldump(1)
NAME
pg_waldump - display a human-readable rendering of the write-ahead log
of a PostgreSQL database cluster
SYNOPSIS
pg_waldump [option...] [startseg [endseg]]
DESCRIPTION
pg_waldump displays the write-ahead log (WAL) and is mainly useful for
debugging or educational purposes.
This utility can only be run by the user who installed the server,
because it requires read-only access to the data directory.
OPTIONS
The following command-line options control the location and format of
the output:
startseg
Start reading at the specified WAL segment file. This implicitly
determines the path in which files will be searched for, and the
timeline to use.
endseg
Stop after reading the specified WAL segment file.
-b
--bkp-details
Output detailed information about backup blocks.
-B block
--block=block
Only display records that modify the given block. The relation must
also be provided with --relation or -R.
-e end
--end=end
Stop reading at the specified WAL location, instead of reading to
the end of the log stream.
-f
--follow
After reaching the end of valid WAL, keep polling once per second
for new WAL to appear.
-F fork
--fork=fork
Only display records that modify blocks in the given fork. The
valid values are main for the main fork, fsm for the free space
map, vm for the visibility map, and init for the init fork.
-n limit
--limit=limit
Display the specified number of records, then stop.
-p path
--path=path
Specifies a directory to search for WAL segment files or a
directory with a pg_wal subdirectory that contains such files. The
default is to search in the current directory, the pg_wal
subdirectory of the current directory, and the pg_wal subdirectory
of PGDATA.
-q
--quiet
Do not print any output, except for errors. This option can be
useful when you want to know whether a range of WAL records can be
successfully parsed but don't care about the record contents.
-r rmgr
--rmgr=rmgr
Only display records generated by the specified resource manager.
You can specify the option multiple times to select multiple
resource managers. If list is passed as name, print a list of valid
resource manager names, and exit.
Extensions may define custom resource managers, but pg_waldump does
not load the extension module and therefore does not recognize
custom resource managers by name. Instead, you can specify the
custom resource managers as custom### where ### is the three-digit
resource manager ID. Names of this form will always be considered
valid.
-R tblspc/db/rel
--relation=tblspc/db/rel
Only display records that modify blocks in the given relation. The
relation is specified with tablespace OID, database OID, and
relfilenode separated by slashes, for example 1234/12345/12345.
This is the same format used for relations in the program's output.
-s start
--start=start
WAL location at which to start reading. The default is to start
reading the first valid WAL record found in the earliest file
found.
-t timeline
--timeline=timeline
Timeline from which to read WAL records. The default is to use the
value in startseg, if that is specified; otherwise, the default is
1. The value can be specified in decimal or hexadecimal, for
example 17 or 0x11.
-V
--version
Print the pg_waldump version and exit.
-w
--fullpage
Only display records that include full page images.
-x xid
--xid=xid
Only display records marked with the given transaction ID.
-z
--stats[=record]
Display summary statistics (number and size of records and
full-page images) instead of individual records. Optionally
generate statistics per-record instead of per-rmgr.
If pg_waldump is terminated by signal SIGINT (Control+C), the
summary of the statistics computed is displayed up to the
termination point. This operation is not supported on Windows.
--save-fullpage=save_path
Save full page images found in the WAL records to the save_path
directory. The images saved are subject to the same filtering and
limiting criteria as the records displayed.
The full page images are saved with the following file name format:
TIMELINE-LSN.RELTABLESPACE.DATOID.RELNODE.BLKNO_FORK The file names
are composed of the following parts:
+--------------+----------------------------+
|Component | Description |
+--------------+----------------------------+
|TIMELINE | The timeline of the WAL |
| | segment file where the |
| | record is |
| | located formatted as one |
| | 8-character hexadecimal |
| | number %08X |
+--------------+----------------------------+
|LSN | The LSN of the record with |
| | this image, |
| | formatted as two |
| | 8-character hexadecimal |
| | numbers |
| | %08X-%08X |
+--------------+----------------------------+
|RELTABLESPACE | tablespace OID of the |
| | block |
+--------------+----------------------------+
|DATOID | database OID of the block |
+--------------+----------------------------+
|RELNODE | filenode of the block |
+--------------+----------------------------+
|BLKNO | block number of the block |
+--------------+----------------------------+
|FORK | The name of the fork the |
| | full page image came from, |
| | such as main, |
| | fsm, vm, or |
| | init. |
+--------------+----------------------------+
-?
--help
Show help about pg_waldump command line arguments, and exit.
ENVIRONMENT
PGDATA
Data directory; see also the -p option.
PG_COLOR
Specifies whether to use color in diagnostic messages. Possible
values are always, auto and never.
NOTES
Can give wrong results when the server is running.
Only the specified timeline is displayed (or the default, if none is
specified). Records in other timelines are ignored.
pg_waldump cannot read WAL files with suffix .partial. If those files
need to be read, .partial suffix needs to be removed from the file
name.
SEE ALSO
Section 28.6
PostgreSQL 17.4 2025 pg_waldump(1)
postgresql 17.4 - Generated Sat Mar 22 11:54:00 CDT 2025