Ubuntu Manpage: pg_waldump - display a human-readable rendering of the write-ahead log of a PostgreSQL

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