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

• 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

• gs_stat_undo()

  Description: Undo statistics.

  Return type: record

  Table 1 gs_stat_undo parameters

  Category	Parameter Name	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