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Undo System Functions

Updated on 2023-10-23 GMT+08:00
  • 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.

    NOTE:

    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.
    • 0MaxBlocNumber: 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.
    • 01048575: 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.
    • 01048575: 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.
    • 01048575: 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.
    • 01048575: 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

    NOTE:

    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

    NOTE:

    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

    NOTE:

    This interface is reserved for expansion and cannot be used.

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