Help Center/ GaussDB/ Centralized_2.x/ SQL Reference/ Functions and Operators/ System Administration Functions/ Undo System Functions

Updated on 2023-10-23 GMT+08:00

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Undo System Functions

gs_undo_meta(type, zoneId, location)

Description: Specifies metadata of each module in the undo system.

Parameter description:

type (metadata type)
The value 0 indicates the metadata corresponding to Undo Zone(Record).

The value 1 indicates the metadata corresponding to Undo Zone(Transaction Slot).

The value 2 indicates the metadata corresponding to Undo Space(Record).

The value 3 indicates the metadata corresponding to Undo Space(Transaction Slot).

zoneId (undo zone ID)
The value –1 indicates the metadata of all undo zones.

The value range 0–1024 x 1024 indicates the metadata of the corresponding zone ID.

location (read location)
The value 0 indicates that data is read from the current memory.

The value 1 indicates that data is read from a physical file.

Return type: record

**Table 1** Output example of gs_undo_meta(0,-1,0)
Category	Parameter	Type	Description
Output parameter	zoneId	oid	ID of the undo zone
Output parameter	persistType	oid	Persistence level
Output parameter	insert	text	Position of the next undo record to be inserted
Output parameter	discard	text	Position of the undo record that is recycled in common mode
Output parameter	end	text	Position of the undo record that is forcibly recycled. Values smaller than the value of this parameter indicate that the record has been recycled.
Output parameter	used	text	Used undo space
Output parameter	lsn	text	LSN to modify the zone
Output parameter	pid	oid	ID of the process bound to the zone

gs_undo_translot(location, zoneId)

Description: Specifies transaction slot information of the undo system.

Parameter description:

location (read location)
The value 0 indicates that data is read from the current memory.

The value 1 indicates that data is read from a physical file.

zoneId (undo zone ID)
The value –1 indicates the metadata of all undo zones.

The value range 0–1024 x 1024 indicates the metadata of the corresponding zone ID.

Return type: record

**Table 2** Output example of gs_undo_translot(0,-1)
Category	Parameter	Type	Description
Output parameter	groupId	oid	ID of the used undo zone
Output parameter	xactId	text	Transaction ID
Output parameter	startUndoPtr	text	Position where the undo record is inserted at the start of the transaction corresponding to a slot
Output parameter	endUndoPtr	text	Position where the undo record is inserted at the end of the transaction corresponding to a slot
Output parameter	lsn	text	Pointer to the corresponding slot
Output parameter	slot_states	oid	Transaction state. The options are as follows: 0: committed; 1: being executed; 2: being rolled back; 3: rolled back

gs_stat_undo()

Description: Undo statistics.

Return type: record

**Table 3** gs_stat_undo parameters
Category	Parameter	Type	Description
Output parameter	curr_used_zone_count	uint32	Number of used undo zones.
Output parameter	top_used_zones	text	Information about the first three undo zones with the maximum usage. The output format is as follows: (zoneId1:Used size; zoneId2:Used size; zoneId3:Used size).
Output parameter	curr_used_undo_size	uint32	Total size of the undo tablespace that is being used. The unit is MB.
Output parameter	undo_threshold	uint32	Calculation result of the value of the GUC parameter undo_space_limit_size x 80%. The unit is MB.
Output parameter	oldest_xid_in_undo	uint64	XID of the transaction recycled to the undo space. The undo records generated by the transaction whose XID is smaller than the value of XID are recycled.
Output parameter	oldest_xmin	uint64	Oldest active transaction.
Output parameter	total_undo_chain_len	int64	Total length of all accessed undo chains.
Output parameter	max_undo_chain_len	int64	Maximum length of the accessed undo chain.
Output parameter	create_undo_file_count	uint32	Number of created undo files.
Output parameter	discard_undo_file_count	uint32	Number of deleted undo files.

gs_undo_record(undoptr)
Description: Undo record resolution.

Parameter description:
- undoptr (undo record pointer)
Return type: record

gs_undo_dump_parsepage_mv(relpath text, blkno bigint, reltype text, rmem boolean)

Description: Parses the page header information of the disk page in the Ustore table, header information of each tuple, flag bit information, and all historical undo version information that can be queried.

Return type: text

Note: Only the system administrator or O&M administrator can execute this function.

Currently, this interface supports only Ustore tables.

**Table 4** gs_undo_dump_parsepage_mv parameters
Category	Parameter	Type	Description
Input parameter	relpath	text	Relative path of the Ustore table data file, in the format of Tablespace name/Database OID/relfilenode. For example, base/16603/16384. You can run the pg_relation_filepath('tablename') command to query the relative path.
Input parameter	blkno	bigint	–1: All block pages are parsed. 0–MaxBlocNumber: A specified block page is parsed.
Input parameter	reltype	text	Table type. Currently, only the Ustore table is supported. The value is uheap.
Input parameter	rmem	boolean	false true Currently, the value can only be false, indicating that the corresponding page is parsed from the disk file.
Output parameter	output	text	Absolute path of the parsing result file.

gs_undo_meta_dump_zone(zone_id int, read_memory boolean)

Description: Parses zone metadata in the undo module.

Return type: record

**Table 5** gs_undo_meta_dump_zone parameters
Category	Parameter	Type	Description
Input parameter	zone_id	int	Undo zone ID –1: All undo zones are queried. 0–1048575: The undo zone metadata is queried based on the zone ID.
Input parameter	read_memory	boolean	true: Data is read from the current memory. false: Data is read from the physical file.
Output parameter	zone_id	int	Undo zone ID
Output parameter	persist_type	int	Persistence level 0: ordinary table 1: unlogged table 2: temporary table
Output parameter	insert	text	Position of the next undo record to be inserted
Output parameter	discard	text	Position of the undo record that is recycled in common mode
Output parameter	forcediscard	text	Position of the undo record that is forcibly recycled. Values smaller than the value of this parameter indicate that the record has been recycled.
Output parameter	lsn	text	LSN to modify the zone

gs_undo_meta_dump_spaces(zone_id int, read_memory boolean)

Description: Parses the metadata of the undo record space and undo slot space in the undo module.

Return type: record

**Table 6** gs_undo_meta_dump_spaces parameters
Category	Parameter	Type	Description
Input parameter	zone_id	int	Undo zone ID –1: All undo zones are queried. 0–1048575: The undo zone metadata is queried based on the zone ID.
Input parameter	read_memory	boolean	true: Data is read from the current memory. false: Data is read from the physical file.
Output parameter	zone_id	int	Undo zone ID
Output parameter	undorecord_space_tail	text	End position of the undo record space
Output parameter	undorecord_space_head	text	Start position of the undo record space
Output parameter	undorecord_space_lsn	text	LSN of the modified undo record space
Output parameter	undoslot_space_tail	text	End position of the undo slot space
Output parameter	undoslot_space_head	text	Start position of the undo slot space
Output parameter	undoreslot_space_lsn	text	LSN of the modified undo slot space

gs_undo_meta_dump_slot(zone_id int, read_memory boolean)

Description: Parses slot metadata in the undo module.

Return type: record

**Table 7** gs_undo_meta_dump_slot parameters
Category	Parameter	Type	Description
Input parameter	zone_id	int	Undo zone ID –1: All undo zones are queried. 0–1048575: The undo zone metadata is queried based on the zone ID.
Input parameter	read_memory	boolean	true: Data is read from the current memory. false: Data is read from the physical file.
Output parameter	zone_id	int	Undo zone ID
Output parameter	allocate	text	Allocation position of the undo transaction slot
Output parameter	recycle	text	Recycling position of the undo transaction slot
Output parameter	frozen_xid	text	Frozen XID, which is used to determine the visibility
Output parameter	global_frozen_xid	text	Minimum frozen XID in the system. Transactions whose XID is smaller than the value of this parameter are visible.
Output parameter	recycle_xid	text	Recycled XID. Transactions whose XID is smaller than the value of this parameter are recycled.
Output parameter	global_recycle_xid	text	Minimum recycled XID in the system. Transactions whose XID is smaller than the value of this parameter are recycled.

gs_undo_translot_dump_slot(zone_id int, read_memory boolean)

Description: Parses slots in a zone.

Return type: record

**Table 8** gs_undo_translot_dump_slot parameters
Category	Parameter	Type	Description
Input parameter	zone_id	oid	Undo zone ID –1: All undo zones are queried. 0–1048575: The undo zone metadata is queried based on the zone ID.
Input parameter	read_memory	boolean	true: Data is read from the current memory. false: Data is read from the physical file.
Output parameter	zone_id	text	Undo zone ID
Output parameter	slot_xid	text	Transaction ID
Output parameter	start_undoptr	text	Position where the undo record is inserted at the start of the transaction corresponding to a slot
Output parameter	end_undoptr	text	Position where the undo record is inserted at the end of the transaction corresponding to a slot
Output parameter	lsn	text	LSN of the modified slot
Output parameter	slot_states	oid	Transaction state 0: committed 1: being executed 2: being rolled back 3: rolled back

gs_undo_translot_dump_xid(slot_xid xid, read_memory boolean)

Description: Parses the slot in a zone based on the XID.

Return type: record

**Table 9** gs_undo_translot_dump_xid parameters
Category	Parameter	Type	Description
Input parameter	slot_xid	xid	XID to be queried
Input parameter	read_memory	boolean	true: Data is read from the current memory. false: Data is read from the physical file.
Output parameter	zone_id	text	Undo zone ID
Output parameter	slot_xid	text	Transaction ID
Output parameter	start_undoptr	text	Position where the undo record is inserted at the start of the transaction corresponding to a slot
Output parameter	end_undoptr	text	Position where the undo record is inserted at the end of the transaction corresponding to a slot
Output parameter	lsn	text	LSN of the modified slot
Output parameter	slot_states	oid	Transaction state 0: committed 1: being executed 2: being rolled back 3: rolled back

gs_undo_dump_record(undoptr bigint)

Description: Parses undo records.

Return type: record

**Table 10** gs_undo_dump_record parameters
Category	Parameter	Type	Description
Input parameter	undoptr	bigint	Start position of the undo record to be parsed
Output parameter	undoptr	bigint	Start position of the undo record to be parsed
Output parameter	xactid	text	Transaction ID
Output parameter	cid	text	command id
Output parameter	reloid	text	relation oid
Output parameter	relfilenode	text	Relfinode of the file
Output parameter	utype	text	Undo record type
Output parameter	blkprev	text	Position of the previous undo record in the same block
Output parameter	blockno	text	Block number
Output parameter	uoffset	text	Undo record offset
Output parameter	prevurp	text	Position of the previous undo record
Output parameter	payloadlen	text	Length of the undo record data
Output parameter	oldxactid	text	Previous XID
Output parameter	partitionoid	text	Partition OID
Output parameter	tablespace	text	Tablespace
Output parameter	alreadyread_bytes	text	Length of the read undo record
Output parameter	prev_undorec_len	text	Length of the previous undo record
Output parameter	td_id	text	ID of the transaction directory
Output parameter	reserved	text	Whether to reserve the record
Output parameter	flag	text	Flag 1
Output parameter	flag2	text	Flag 2
Output parameter	t_hoff	text	Length of the undo record data header

gs_undo_dump_xid(undo_xid xid)

Description: Parses undo records based on the XID.

Return type: record

**Table 11** gs_undo_dump_xid parameters
Category	Parameter	Type	Description
Input parameter	undo_xid	xid	XID
Output parameter	undoptr	xid	Start position of the undo record to be parsed
Output parameter	xactid	text	XID
Output parameter	cid	text	command id
Output parameter	reloid	text	relation oid
Output parameter	relfilenode	text	Relfinode of the file
Output parameter	utype	text	Undo record type
Output parameter	blkprev	text	Position of the previous undo record in the same block
Output parameter	blockno	text	Block number
Output parameter	uoffset	text	Undo record offset
Output parameter	prevurp	text	Position of the previous undo record
Output parameter	payloadlen	text	Length of the undo record data
Output parameter	oldxactid	text	Previous XID
Output parameter	partitionoid	text	Partition OID
Output parameter	tablespace	text	Tablespace
Output parameter	alreadyread_bytes	text	Length of the read undo record
Output parameter	prev_undorec_len	text	Length of the previous undo record
Output parameter	td_id	text	ID of the transaction directory
Output parameter	reserved	text	Whether to reserve the record
Output parameter	flag	text	Flag 1
Output parameter	flag2	text	Flag 2
Output parameter	t_hoff	text	Length of the undo record data header

gs_verify_undo_record(type, startIdx, endIdx, location)
Description: Verifies the Undo record.

Return type: record

This interface is reserved for expansion and cannot be used.

gs_verify_undo_translot(type, startIdx, endIdx, location)
Description: Verifies the Undo transaction slot.

Return type: record

This interface is reserved for expansion and cannot be used.

gs_verify_undo_meta(type, startIdx, endIdx, location)
Description: Verifies the Undo meta information.

Return type: record

This interface is reserved for expansion and cannot be used.