Wiki / Command-line Tools / Server applications

pg_waldump

pg_waldump — display a human-readable rendering of the write-ahead log of a PostgreSQL database cluster

Reading PostgreSQL 18.6.

Description

pg_waldump — display a human-readable rendering of the write-ahead log of a PostgreSQL database cluster

Documented executable: pg_waldump
Executable version: 18.6
Reference inventory: Server applications
Option definition groups: 18

Usage

pg_waldump [ option ...] [ startseg [ endseg ]]

Documented options

Option and arguments	Description
-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.
-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.
--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.
-? --help	Show help about pg_waldump command line arguments, and exit.

Environment variables

Variable	Meaning
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 .

Manual definition

pg_waldump

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.

Documentation and source

Source build

Version: 18.6
Build: https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2
Source fingerprint: ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8

Compare versions

PostgreSQL 14 → 15: changed.

--- PostgreSQL 14
+++ PostgreSQL 15
@@ -19,6 +19,14 @@
       "signature": "-b --bkp-details"
     },
     {
+      "description": "Only display records that modify the given block. The relation must also be provided with --relation or -R .",
+      "names": [
+        "-B block",
+        "--block= block"
+      ],
+      "signature": "-B block --block= block"
+    },
+    {
       "description": "Stop reading at the specified WAL location, instead of reading to the end of the log stream.",
       "names": [
         "-e end",
@@ -33,6 +41,14 @@
         "--follow"
       ],
       "signature": "-f --follow"
+    },
+    {
+      "description": "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.",
+      "names": [
+        "-F fork",
+        "--fork= fork"
+      ],
+      "signature": "-F fork --fork= fork"
     },
     {
       "description": "Display the specified number of records, then stop.",
@@ -59,12 +75,20 @@
       "signature": "-q --quiet"
     },
     {
-      "description": "Only display records generated by the specified resource manager. If list is passed as name, print a list of valid resource manager names, and exit.",
+      "description": "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.",
       "names": [
         "-r rmgr",
         "--rmgr= rmgr"
       ],
       "signature": "-r rmgr --rmgr= rmgr"
+    },
+    {
+      "description": "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.",
+      "names": [
+        "-R tblspc / db / rel",
+        "--relation= tblspc / db / rel"
+      ],
+      "signature": "-R tblspc / db / rel --relation= tblspc / db / rel"
     },
     {
       "description": "WAL location at which to start reading. The default is to start reading the first valid log record found in the earliest file found.",
@@ -91,6 +115,14 @@
       "signature": "-V --version"
     },
     {
+      "description": "Only display records that include full page images.",
+      "names": [
+        "-w",
+        "--fullpage"
+      ],
+      "signature": "-w --fullpage"
+    },
+    {
       "description": "Only display records marked with the given transaction ID.",
       "names": [
         "-x xid",
@@ -99,7 +131,7 @@
       "signature": "-x xid --xid= xid"
     },
     {
-      "description": "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.",
+      "description": "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 .",
       "names": [
         "-z",
         "--stats[=record]"

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

Export JSON · Back to Command-line Tools · Recorded in PostgreSQL 10 through 20; the first sample is not necessarily its introduction.

Description

Usage

Documented options

Environment variables

Manual definition

pg_waldump

Synopsis

Description

Options

Environment

Notes

See Also

Documentation and source

Compare versions

Related entries