pg_waldump

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

Synopsis

pg_waldump [option...] [timestamp-option...] [startseg [endseg] ]

Description

pg_waldump displays the write-ahead log (WAL) and prints timestamps for WAL records. This utility 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 log 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 log segment file.

-b
--bkp-details

Output detailed information about backup blocks.

-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.

-n limit
--limit=limit

Display the specified number of records, then stop.

-p path
--path=path

Specifies a directory to search for log 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.

-r rmgr
--rmgr=rmgr

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.

-s start
--start=start

WAL location at which to start reading. The default is to start reading the first valid log record found in the earliest file found.

-t timeline
--timeline=timeline

Timeline from which to read log records. The default is to use the value in startseg, if that is specified; otherwise, the default is 1.

-V
--version

Print the pg_waldump version and exit.

-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.

-?
--help

Show help about pg_waldump command line arguments, and exit.

The following command-line options enable printing timestamps for various types of WAL records. You can use these options together with startseg, endseg, -s, and -e options.

-E

Print the timestamp of the last WAL record of the specified type found in the log segment file. When using this option, you must also specify the -S option.

By default, pg_waldump prints timestamps only for COMMIT records. You can specify other record types using the -F option.

-F [argument1,argument2,...]

Specify WAL record types for which to print timestamps. When using this option, you must also specify the -S option.

The -F option can take the following arguments, in the comma-separated format:

  • XLOG_RESTORE_POINT — named restore points created with the pg_create_restore_point() function.

  • XLOG_XACT_COMMIT — commit records for transactions. These records are caused by the COMMIT command.

  • XLOG_XACT_COMMIT_PREPARED — commit records for transactions that were earlier prepared for a two-phase commit. These records are caused by the COMMIT PREPARED command.

  • XLOG_XACT_ABORT — abort records for transactions. These records are caused by the ROLLBACK command.

  • XLOG_XACT_ABORT_PREPARED — abort records for transactions that were earlier prepared for a two-phase commit. These records are caused by the ROLLBACK PREPARED command.

By default, pg_waldump prints timestamps only for COMMIT records.

-S

Print the timestamp of the first WAL record of the specified type found in the log segment file. This option is required if you are going to use -E or -F options.

By default, pg_waldump prints timestamps only for COMMIT records. You can specify other record types using the -F option.

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.