Help Center > > Developer Guide> SQL Reference> Functions and Operators> Replication Functions:

Replication Functions:

Updated at: Jul 15, 2020 GMT+08:00

A replication function synchronizes logs and data between instances. It is a statistics or operation method provided by the system to implement HA.

Replication functions except statistics queries are internal functions. You are not advised to use them directly.

  • pg_create_logical_replication_slot('slot_name', 'plugin_name')

    Description: Creates a logical replication slot.

    Parameter:

    • slot_name

      Indicates the name of the streaming replication slot.

      Value range: a string, supporting only letters, digits, and the following special characters: _?-.

    • plugin_name

      Indicates the name of the plugin.

      Value range: a string, supporting only mppdb_decoding

    Return type: name, text

    Note: The first return value is the slot name, and the second is the start LSN position for decoding in the logical replication slot.

  • pg_create_physical_replication_slot ('slot_name', isDummyStandby)

    Description: Creates a physical replication slot.

    Parameter:

    • slot_name

      Indicates the name of the streaming replication slot.

      Value range: a string, supporting only letters, digits, and the following special characters: _?.-

    • isDummyStandby

      Indicates whether the replication slot is the secondary one.

      Value range: a boolean value, true or false

    Return type: name, text

    Note: The first return value is the slot name, and the second is the start LSN position for decoding in the physical replication slot.

  • pg_get_replication_slots()

    Description: Displays information about all replication slots on the current DN.

    Return type: record

    The following information is returned:

    Table 1 pg_get_replication_slots() fields

    Field

    Type

    Description

    slot_name

    text

    Replication slot name

    plugin

    name

    Name of the output plug-in of the logical replication slot

    slot_type

    text

    Replication slot type

    datoid

    oid

    Replication slot's database OID

    active

    boolean

    Whether the replication slot is active

    xmin

    xid

    Transaction ID of the replication slot

    catalog_xmin

    restart_lsn

    dummy_standby

    text

    text

    boolean

    ID of the earliest-decoded transaction corresponding to the logical replication slot.

    Xlog file information on the replication slot.

    Indicates whether the replication slot is the secondary one.

  • pg_drop_replication_slot('slot_name')

    Description: Deletes a streaming replication slot.

    Parameter:

    • slot_name

      Indicates the name of the streaming replication slot.

      Value range: a string, supporting only letters, digits, and the following special characters: _?-.

    Return type: void

  • pg_logical_slot_peek_changes('slot_name', 'LSN', upto_nchanges, 'options_name', 'options_value')

    Description: Performs decoding but does not go to the next streaming replication slot. (The decoding result will be returned again on future calls.)

    Parameter:

    • slot_name

      Indicates the name of the streaming replication slot.

      Value range: a string, supporting only letters, digits, and the following special characters: _?-.

    • LSN

      Indicates a target LSN. Decoding is performed only when an LSN is less than or equal to this value.

      Value range: a string, in the format of xlogid/xrecoff, for example, '1/2AAFC60' (If this parameter is set to NULL, the target LSN indicating the end position of decoding is not specified.)

    • upto_nchanges

      Indicates the number of decoded records (including the begin and commit timestamps). Assume that there are three transactions, which involve 3, 5, and 7 records, respectively. If upto_nchanges is 4, 8 records of the first two transactions will be decoded. Specifically, decoding is stopped when the number of decoded records exceeds 4 after decoding in the first two transactions is finished.

      Value range: a non-negative integer

      If any of the LSN and upto_nchanges values are reached, decoding ends.

    • options (optional)
      • include-xids

        Indicates whether the decoded data column contains XID information.

        Valid value: 0 and 1. The default value is 1.

        • 0: The decoded data column does not contain XID information.
        • 1: The decoded data column contains XID information.
      • skip-empty-xacts

        Indicates whether to ignore empty transaction information during decoding.

        Valid value: 0 and 1. The default value is 0.

        • 0: The empty transaction information is not ignored during decoding.
        • 1: The empty transaction information is ignored during decoding.
      • include-timestamp

        Indicates whether decoding information contains the commit timestamp.

        Valid value: 0 and 1. The default value is 0.

        • 0: The decoding information does not contain the commit timestamp.
        • 1: The decoding information contains the commit timestamp.

    Return type: text, uint, text

    Note: The function returns the decoding result. Each decoding result contains three columns, corresponding to the above return types and indicating the LSN position, XID, and decoded content, respectively.

  • pg_logical_slot_get_changes('slot_name', 'LSN', upto_nchanges, 'options_name', 'options_value')

    Description: Performs decoding and goes to the next streaming replication slot.

    Parameter: This function has the same parameters as pg_logical_slot_peek_changes. For details, see pg_logical_slot_peek_ch....

  • pg_replication_slot_advance ('slot_name', 'LSN')

    Description: Directly goes to the streaming replication slot for a specified LSN, without outputting any decoding result.

    Parameter:

    • slot_name

      Indicates the name of the streaming replication slot.

      Value range: a string, supporting only letters, digits, and the following special characters: _?-.

    • LSN

      Indicates a target LSN. Next decoding will be performed only in transactions whose commission position is greater than this value. If an input LSN is smaller than the position recorded in the current streaming replication slot, the function directly returns. If the input LSN is greater than the LSN of the current physical log, the latter LSN will be directly used for decoding.

      Value range: a string, in the format of xlogid/xrecoff

    Return type: name, text

    Note: A return result contains the slot name and LSN that is actually used for decoding.

  • pg_stat_get_data_senders()

    Description: Displays statistics about replication sending threads on all data page on the current DN.

    Return type: record

    The following information is returned:

    Table 2 pg_stat_get_data_senders() fields

    Field

    Type

    Description

    pid

    bigint

    Thread PID

    sender_pid

    integer

    Current sender PID

    local_role

    text

    Local role

    peer_role

    text

    Peer role

    state

    text

    Current sender's replication status

    catchup_start

    timestamp with time zone

    Startup time of a catchup task

  • pg_stat_get_wal_senders()

    Description: Displays statistics about replication sending threads on all WALs on the current DN.

    Return type: record

    The following information is returned:

    Table 3 pg_stat_get_wal_senders() fields

    Field

    Type

    Description

    pid

    bigint

    Thread PID

    sender_pid

    integer

    Current sender PID

    local_role

    text

    Local role

    peer_role

    text

    Peer role

    peer_state

    text

    Peer status

    state

    text

    Current sender's replication status

    catchup_start

    timestamp with time zone

    Startup time of a catchup task

    catchup_end

    timestamp with time zone

    End time of a catchup task

    sender_sent_location

    text

    Location where the sender sends LSNs

    sender_write_location

    text

    Location where the sender writes LSNs

    sender_flush_location

    text

    Location where the sender flushes LSNs

    sender_replay_location

    text

    Location where the sender replays LSNs

    receiver_received_location

    text

    Location where the receiver receives LSNs

    receiver_write_location

    text

    Location where the receiver writes LSNs

    receiver_flush_location

    text

    Location where the receiver flushes LSNs

    receiver_replay_location

    text

    Location where the receiver replays LSNs

    sync_percent

    text

    Specifies the synchronization percentage.

    sync_state

    text

    Synchronization state (asynchronous duplication, synchronous duplication, or potential synchronization)

    sync_priority

    integer

    Priority of synchronous duplication (0 indicates asynchronization)

    sync_most_available

    text

    Whether to block the active node when the synchronization on the standby node fails

    channel

    text

    WALSender channel information

  • pg_stat_get_wal_receiver()

    Description: Displays statistics about replication receiving threads on all WALs on the current DN.

    Return type: record

    The following information is returned:

    Table 4 pg_stat_get_wal_receiver()

    Field

    Type

    Description

    receiver_pid

    integer

    Current receiver PID

    local_role

    text

    Local role

    peer_role

    text

    Peer role

    peer_state

    text

    Peer status

    state

    text

    Current receiver's replication status

    sender_sent_location

    text

    Location where the sender sends LSNs

    sender_write_location

    text

    Location where the sender writes LSNs

    sender_flush_location

    text

    Location where the sender flushes LSNs

    sender_replay_location

    text

    Location where the sender replays LSNs

    receiver_received_location

    text

    Location where the receiver receives LSNs

    receiver_write_location

    text

    Location where the receiver writes LSNs

    receiver_flush_location

    text

    Location where the receiver flushes LSNs

    receiver_replay_location

    text

    Location where the receiver replays LSNs

    sync_percent

    text

    Specifies the synchronization percentage.

    channel

    text

    WALReceiver channel information

  • pg_stat_get_stream_replications()

    Description: Displays information about all replication statistics on the current DN.

    Return type: record

    The following information is returned:

    Table 5 pg_stat_get_stream_replications()

    Field

    Type

    Description

    local_role

    text

    Local role

    static_connections

    integer

    Connection statistics

    db_state

    text

    Database status

    detail_information

    text

    Detail information

Did you find this page helpful?

Submit successfully!

Thank you for your feedback. Your feedback helps make our documentation better.

Failed to submit the feedback. Please try again later.

Which of the following issues have you encountered?







Please complete at least one feedback item.

Content most length 200 character

Content is empty.

OK Cancel