Replication Functions

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:

Example:

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SELECT * FROM pg_get_replication_slots();
    slot_name    | plugin | slot_type | datoid | active | xmin | catalog_xmin |    restart_lsn    | dummy_standby
-----------------+--------+-----------+--------+--------+------+--------------+-------------------+---------------
 gs_roach_common |        | physical  |      0 | f      |      |    602861775 | FFFFFFFF/FFFFFFFF | f
(1 row)

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_changes('slot_name', 'LSN', upto_nchanges, 'options_name', 'options_value').

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:

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:

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:

pg_stat_get_stream_replications()

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

Return type: record

The following information is returned:

Example:

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SELECT * FROM pg_stat_get_stream_replications();
 local_role | static_connections | db_state | detail_information
------------+--------------------+----------+--------------------
 Normal     |                  0 | Normal   | Normal
(1 row)

pg_stat_xlog_space()

Description: Displays the Xlog space usage on the current DN.

Return type: record

The following information is returned:

Example:

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SELECT * FROM pg_stat_xlog_space();
 xlog_files | xlog_size | other_size
------------+-----------+------------
         79 |      1264 |          0
(1 row)

pgxc_stat_xlog_space()

Description: Displays the Xlog space usage on all active DNs.

Return type: record

The following information is returned:

Example:

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 SELECT * FROM  pgxc_stat_xlog_space();
  node_name   | xlog_files | xlog_size | other_size
--------------+------------+-----------+------------
 dn_6001_6002 |         73 |      1168 |          0
 dn_6003_6004 |         73 |      1168 |          0
 dn_6005_6006 |         73 |      1168 |          0
 cn_5003      |         79 |      1264 |          0
 cn_5001      |         72 |      1152 |          0
 cn_5002      |         73 |      1168 |          0
(6 rows)