qhb_waldump

qhb_waldump — display a human-readable rendering of the write-ahead log of a QHB database cluster

Synopsis

qhb_waldump [option...] [startseg [endseg]]

Description

qhb_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 qhb_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 qhb_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 qhb_waldump is terminated by signal SIGINT (Control+C), the summary of the statistics computed is displayed up to the termination point.

--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 qhb_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.

qhb_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.