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PG_WALDUMP(1) PostgreSQL 16.1 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

If provided, 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.BLKNOFORK 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 30.6

2023 PostgreSQL 16.1