Replication Functions
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.
- slot_name
- 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.
- slot_name
- 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
- slot_name
- 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.
- include-xids
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.
- slot_name
- 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.
- slot_name
- 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
catchup_end
timestamp with time zone
End time of a catchup task
queue_size
text
Data queue size
queue_lower_tail
text
Position of data queue tail 1
queue_header
text
Position of data queue header
queue_upper_tail
text
Position of data queue tail 2
send_position
text
Sending position of the sender
receive_position
text
Receiving position of the receiver
catchup_type
text
Catchup task type, full or incremental
catchup_bcm_filename
text
BCM file executed by the current catchup task
catchup_bcm_finished
integer
Number of BCM files completed by a catchup task
catchup_bcm_total
integer
Total number of BCM files to be operated by a catchup task
catchup_percent
text
Completion percentage of a catchup task
catchup_remaining_time
text
Estimated remaining 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
- pg_stat_xlog_space()
Description: Displays the Xlog space usage on the current DN.
Return type: record
The following information is returned:
Table 6 pg_stat_xlog_space() Column
Type
Description
xlog_files
bigint
Number of all identified xlog files in the pg_xlog directory, excluding the backup and archive_status subdirectories.
xlog_size
bigint
Total size (MB) of all identified xlog files in the pg_xlog directory, excluding the backup and archive_status subdirectories.
other_size
bigint
Total size (MB) of files in the backup and archive_status subdirectories of the pg_xlog directory.
- pgxc_stat_xlog_space()
Description: Displays the Xlog space usage on all active DNs.
Return type: record
The following information is returned:
Table 7 pgxc_stat_xlog_space() Column
Type
Description
node_name
name
Node name
xlog_files
bigint
Number of all identified xlog files in the pg_xlog directory, excluding the backup and archive_status subdirectories.
xlog_size
bigint
Total size (MB) of all identified xlog files in the pg_xlog directory, excluding the backup and archive_status subdirectories.
other_size
bigint
Total size (MB) of files in the backup and archive_status subdirectories of the pg_xlog directory.
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