patroni.dcs package

Submodules

Module contents

Abstract classes for Distributed Configuration Store.

class patroni.dcs. AbstractDCS ( config : Dict [ str , Any ] , mpp : AbstractMPP ) View on GitHub

Bases: ABC

Abstract representation of DCS modules.

Implementations of a concrete DCS class, using appropriate backend client interfaces, must include the following methods and properties.

Functional methods that are critical in their timing, required to complete within retry_timeout period in order to prevent the DCS considered inaccessible, each perform construction of complex data objects:

• _postgresql_cluster_loader() :

  method which processes the structure of data stored in the DCS used to build the Cluster object with all relevant associated data.

• _mpp_cluster_loader() :

  Similar to above but specifically representing MPP group and workers information.

• _load_cluster() :

  main method for calling specific loader method to build the Cluster object representing the state and topology of the cluster.

Functional methods that are critical in their timing and must be written with ACID transaction properties in mind:

• attempt_to_acquire_leader() :

  method used in the leader race to attempt to acquire the leader lock by creating the leader key in the DCS, if it does not exist.

• _update_leader() :

  method to update leader key in DCS. Relies on Compare-And-Set to ensure the Primary lock key is updated. If this fails to update within the retry_timeout window the Primary will be demoted.

Functional method that relies on Compare-And-Create to ensure only one member creates the relevant key:

• initialize() :

  method used in the race for cluster initialization which creates the initialize key in the DCS.

DCS backend getter and setter methods and properties:

• take_leader() : method to create a new leader key in the DCS.

• set_ttl() : method for setting TTL value in DCS.

• ttl() : property which returns the current TTL.

• set_retry_timeout() : method for setting retry_timeout in DCS backend.

• _write_leader_optime() : compatibility method to write WAL LSN to DCS.

• _write_status() : method to write WAL LSN for slots to the DCS.

• _write_failsafe() : method to write cluster topology to the DCS, used by failsafe mechanism.

• touch_member() : method to update individual member key in the DCS.

• set_history_value() : method to set the history key in the DCS.

DCS setter methods using Compare-And-Set which although important are less critical if they fail, attempts can be retried or may result in warning log messages:

• set_failover_value() : method to create and/or update the failover key in the DCS.

• set_config_value() : method to create and/or update the failover key in the DCS.

• set_sync_state_value() : method to set the synchronous state sync key in the DCS.

DCS data and key removal methods:

• delete_sync_state() :

  likewise, a method to remove synchronous state sync key from the DCS.

• delete_cluster() :

  method which will remove cluster information from the DCS. Used only from patronictl .

• _delete_leader() :

  method relies on CAS, used by a member that is the current leader, to remove the leader key in the DCS.

• cancel_initialization() :

  method to remove the initialize key for the cluster from the DCS.

If either of the sync_state set or delete methods fail, although not critical, this may result in Synchronous replication key updated by someone else messages being logged.

Care should be taken to consult each abstract method for any additional information and requirements such as expected exceptions that should be raised in certain conditions and the object types for arguments and return from methods and properties.

_CONFIG = 'config'

_FAILOVER = 'failover'

_FAILSAFE = 'failsafe'

_HISTORY = 'history'

_INITIALIZE = 'initialize'

_LEADER = 'leader'

_LEADER_OPTIME = 'optime/leader'

_MEMBERS = 'members/'

_OPTIME = 'optime'

_STATUS = 'status'

_SYNC = 'sync'

__get_postgresql_cluster ( path : str | None = None ) → Cluster

Low level method to load a Cluster object from DCS.

Parameters :

path – optional client path in DCS backend to load from.

Returns :

a loaded Cluster instance.

__init__ ( config : Dict [ str , Any ] , mpp : AbstractMPP ) → None View on GitHub

Prepare DCS paths, MPP object, initial values for state information and processing dependencies.

Parameters :

• config – dict , reference to config section of selected DCS. i.e.: zookeeper for zookeeper, etcd for etcd, etc…

• mpp – an object implementing AbstractMPP interface.

_abc_impl = <_abc._abc_data object>

_build_retain_slots ( cluster : Cluster , slots : Dict [ str , int ] | None ) → List [ str ] | None View on GitHub

Handle retention policy of physical replication slots for cluster members.

When the member key is missing we want to keep its replication slot for a while, so that WAL segments will not be already absent when it comes back online. It is being solved by storing the list of replication slots representing members in the retain_slots field of the /status key.

This method handles retention policy by keeping the list of such replication slots in memory and removing names when they were observed longer than member_slots_ttl ago.

Parameters :

• cluster – Cluster object with information about the current cluster state.

• slots – slot names with LSN values that exist on the leader node and consists of slots for cluster members and permanent replication slots.

Returns :

the list of replication slots to be written to /status key or None .

abstract _delete_leader ( leader : Leader ) → bool View on GitHub

Remove leader key from DCS.

This method should remove leader key if current instance is the leader.

Parameters :

leader – Leader object with information about the leader.

Returns :

True if successfully committed to DCS.

_get_mpp_cluster ( ) → Cluster View on GitHub

Load MPP cluster from DCS.

Returns :

A MPP Cluster instance for the coordinator with workers clusters in the Cluster.workers dict.

abstract _load_cluster ( path : str , loader : Callable [ [ Any ] , Cluster | Dict [ int , Cluster ] ] ) → Cluster | Dict [ int , Cluster ] View on GitHub

Main abstract method that implements the loading of Cluster instance.

Note

Internally this method should call the loader method that will build Cluster object which represents current state and topology of the cluster in DCS. This method supposed to be called only by the get_cluster() method.

Parameters :

• path – the path in DCS where to load Cluster(s) from.

• loader – one of _postgresql_cluster_loader() or _mpp_cluster_loader() .

Raise :

DCSError in case of communication problems with DCS. If the current node was running as a primary and exception raised, instance would be demoted.

abstract _mpp_cluster_loader ( path : Any ) → Dict [ int , Cluster ] View on GitHub

Load and build all PostgreSQL clusters from a single MPP cluster.

Parameters :

path – the path in DCS where to load Cluster(s) from.

Returns :

all MPP groups as dict , with group IDs as keys and Cluster objects as values.

abstract _postgresql_cluster_loader ( path : Any ) → Cluster View on GitHub

Load and build the Cluster object from DCS, which represents a single PostgreSQL cluster.

Parameters :

path – the path in DCS where to load Cluster from.

Returns :

Cluster instance.

_set_loop_wait ( loop_wait : int ) → None View on GitHub

Set new loop_wait value.

Parameters :

loop_wait – value to set.

abstract _update_leader ( leader : Leader ) → bool View on GitHub

Update leader key (or session) ttl.

Note

You have to use CAS (Compare And Swap) operation in order to update leader key, for example for etcd prevValue parameter must be used.

If update fails due to DCS not being accessible or because it is not able to process requests (hopefully temporary), the DCSError exception should be raised.

Parameters :

leader – a reference to a current leader object.

Returns :

True if leader key (or session) has been updated successfully.

abstract _write_failsafe ( value : str ) → bool View on GitHub

Write current cluster topology to DCS that will be used by failsafe mechanism (if enabled).

Parameters :

value – failsafe topology serialized in JSON format.

Returns :

True if successfully committed to DCS.

abstract _write_leader_optime ( last_lsn : str ) → bool View on GitHub

Write current WAL LSN into /optime/leader key in DCS.

Parameters :

last_lsn – absolute WAL LSN in bytes.

Returns :

True if successfully committed to DCS.

abstract _write_status ( value : str ) → bool View on GitHub

Write current WAL LSN and confirmed_flush_lsn of permanent slots into the /status key in DCS.

Parameters :

value – status serialized in JSON format.

Returns :

True if successfully committed to DCS.

abstract attempt_to_acquire_leader ( ) → bool View on GitHub

Attempt to acquire leader lock.

Note

This method should create /leader key with the value _name .

The key must be created atomically. In case the key already exists it should not be overwritten and False must be returned.

If key creation fails due to DCS not being accessible or because it is not able to process requests (hopefully temporary), the DCSError exception should be raised.

Returns :

True if key has been created successfully.

abstract cancel_initialization ( ) → bool View on GitHub

Removes the initialize key for a cluster.

Returns :

True if successfully committed to DCS.

client_path ( path : str ) → str View on GitHub

Construct the absolute key name from appropriate parts for the DCS type.

Parameters :

path – The key name within the current Patroni cluster.

Returns :

absolute key name for the current Patroni cluster.

property cluster : Cluster | None View on GitHub

Cached DCS cluster information that has not yet expired.

property config_path : str View on GitHub

Get the client path for config .

abstract delete_cluster ( ) → bool View on GitHub

Delete cluster from DCS.

Returns :

True if successfully committed to DCS.

delete_leader ( leader : Leader | None , last_lsn : int | None = None ) → bool View on GitHub

Update optime/leader and voluntarily remove leader key from DCS.

This method should remove leader key if current instance is the leader.

Parameters :

• leader – Leader object with information about the leader.

• last_lsn – latest checkpoint location in bytes.

Returns :

boolean result of called abstract _delete_leader() .

abstract delete_sync_state ( version : Any | None = None ) → bool View on GitHub

Delete the synchronous state from DCS.

Parameters :

version – for conditional deletion of the key/object.

Returns :

True if delete successful.

property failover_path : str View on GitHub

Get the client path for failover .

property failsafe : Dict [ str , str ] | None View on GitHub

Stored value of _last_failsafe .

property failsafe_path : str View on GitHub

Get the client path for failsafe .

get_cluster ( ) → Cluster View on GitHub

Retrieve a fresh view of DCS.

Note

Stores copy of time, status and failsafe values for comparison in DCS update decisions. Caching is required to avoid overhead placed upon the REST API.

Returns either a PostgreSQL or MPP implementation of Cluster depending on availability.

Returns :

get_mpp_coordinator ( ) → Cluster | None View on GitHub

Load the PostgreSQL cluster for the MPP Coordinator.

Note

This method is only executed on the worker nodes to find the coordinator.

Returns :

Select Cluster instance associated with the MPP Coordinator group ID.

property history_path : str View on GitHub

Get the client path for history .

abstract initialize ( create_new : bool = True , sysid : str = '' ) → bool View on GitHub

Race for cluster initialization.

This method should atomically create initialize key and return True , otherwise it should return False .

Parameters :

• create_new – False if the key should already exist (in the case we are setting the system_id).

• sysid – PostgreSQL cluster system identifier, if specified, is written to the key.

Returns :

True if key has been created successfully.

property initialize_path : str View on GitHub

Get the client path for initialize .

is_mpp_coordinator ( ) → bool View on GitHub

Cluster instance has a Coordinator group ID.

Returns :

True if the given node is running as the MPP Coordinator.

property last_seen : int View on GitHub

The time recorded when the DCS was last reachable.

property leader_optime_path : str View on GitHub

Get the client path for optime/leader (legacy key, superseded by status ).

property leader_path : str View on GitHub

Get the client path for leader .

property loop_wait : int View on GitHub

The recorded value for cluster HA loop wait time in seconds.

manual_failover ( leader : str | None , candidate : str | None , scheduled_at : datetime | None = None , version : Any | None = None ) → bool View on GitHub

Prepare dictionary with given values and set /failover key in DCS.

Parameters :

• leader – value to set for leader .

• candidate – value to set for member .

• scheduled_at – value converted to ISO date format for scheduled_at .

• version – for conditional update of the key/object.

Returns :

True if successfully committed to DCS.

property member_path : str View on GitHub

Get the client path for member representing this node.

property members_path : str View on GitHub

Get the client path for members .

property mpp : AbstractMPP View on GitHub

Get the effective underlying MPP, if any has been configured.

reload_config ( config : Config | Dict [ str , Any ] ) → None View on GitHub

Load and set relevant values from configuration.

Sets loop_wait , ttl and retry_timeout properties.

Parameters :

config – Loaded configuration information object or dictionary of key value pairs.

reset_cluster ( ) → None View on GitHub

Clear cached state of DCS.

abstract set_config_value ( value : str , version : Any | None = None ) → bool View on GitHub

Create or update /config key in DCS.

Parameters :

• value – new value to set in the config key.

• version – for conditional update of the key/object.

Returns :

True if successfully committed to DCS.

abstract set_failover_value ( value : str , version : Any | None = None ) → bool View on GitHub

Create or update /failover key.

Parameters :

• value – value to set.

• version – for conditional update of the key/object.

Returns :

True if successfully committed to DCS.

abstract set_history_value ( value : str ) → bool View on GitHub

Set value for history in DCS.

Parameters :

value – new value of history key/object.

Returns :

True if successfully committed to DCS.

abstract set_retry_timeout ( retry_timeout : int ) → None View on GitHub

Set the new value for retry_timeout .

abstract set_sync_state_value ( value : str , version : Any | None = None ) → Any | bool View on GitHub

Set synchronous state in DCS.

Parameters :

• value – the new value of /sync key.

• version – for conditional update of the key/object.

Returns :

version of the new object or False in case of error.

abstract set_ttl ( ttl : int ) → bool | None View on GitHub

Set the new ttl value for DCS keys.

property status_path : str View on GitHub

Get the client path for status .

property sync_path : str View on GitHub

Get the client path for sync .

static sync_state ( leader : str | None , sync_standby : Collection [ str ] | None , quorum : int | None ) → Dict [ str , Any ] View on GitHub

Build sync_state dictionary.

Parameters :

• leader – name of the leader node that manages /sync key.

• sync_standby – collection of currently known synchronous standby node names.

• quorum – if the node from sync_standby list is doing a leader race it should see at least quorum other nodes from the sync_standby + leader list

Returns :

dictionary that later could be serialized to JSON or saved directly to DCS.

abstract take_leader ( ) → bool View on GitHub

Establish a new leader in DCS.

Note

This method should create leader key with value of _name and ttl of ttl .

Since it could be called only on initial cluster bootstrap it could create this key regardless, overwriting the key if necessary.

Returns :

True if successfully committed to DCS.

abstract touch_member ( data : Dict [ str , Any ] ) → bool View on GitHub

Update member key in DCS.

Note

This method should create or update key with the name with /members/ + _name and the value of data in a given DCS.

Parameters :

data – information about an instance (including connection strings).

Returns :

True if successfully committed to DCS.

abstract property ttl : int View on GitHub

Get current ttl value.

update_leader ( cluster : Cluster , last_lsn : int | None , slots : Dict [ str , int ] | None = None , failsafe : Dict [ str , str ] | None = None ) → bool View on GitHub

Update leader key (or session) ttl, /status , and /failsafe keys.

Parameters :

• cluster – Cluster object with information about the current cluster state.

• last_lsn – absolute WAL LSN in bytes.

• slots – dictionary with permanent slots confirmed_flush_lsn .

• failsafe – if defined dictionary passed to write_failsafe() .

Returns :

True if leader key (or session) has been updated successfully.

watch ( leader_version : Any | None , timeout : float ) → bool View on GitHub

Sleep if the current node is a leader, otherwise, watch for changes of leader key with a given timeout .

Parameters :

• leader_version – version of a leader key.

• timeout – timeout in seconds.

Returns :

if True this will reschedule the next run of the HA cycle.

write_failsafe ( value : Dict [ str , str ] ) → None View on GitHub

Write the /failsafe key in DCS.

Parameters :

value – dictionary value to set, consisting of the name and api_url of members.

write_leader_optime ( last_lsn : int ) → None View on GitHub

Write value for WAL LSN to optime/leader key in DCS.

Note

This method abstracts away the required data structure of write_status() , so it is not needed in the caller. However, the optime/leader is only written in write_status() when the cluster has members with a Patroni version that is old enough to require it (i.e. the old Patroni version doesn’t understand the new format).

Parameters :

last_lsn – absolute WAL LSN in bytes.

write_status ( value : Dict [ str , Any ] ) → None View on GitHub

Write cluster status to DCS if changed.

Note

The DCS key /status was introduced in Patroni version 2.1.0. Previous to this the position of last known leader LSN was stored in optime/leader . This method has detection for backwards compatibility of members with a version older than this.

Parameters :

value – JSON serializable dictionary with current WAL LSN and confirmed_flush_lsn of permanent slots.

write_sync_state ( leader : str | None , sync_standby : Collection [ str ] | None , quorum : int | None , version : Any | None = None ) → SyncState | None View on GitHub

Write the new synchronous state to DCS.

Calls sync_state() to build a dictionary and then calls DCS specific set_sync_state_value() .

Parameters :

• leader – name of the leader node that manages /sync key.

• sync_standby – collection of currently known synchronous standby node names.

• version – for conditional update of the key/object.

• quorum – if the node from sync_standby list is doing a leader race it should see at least quorum other nodes from the sync_standby + leader list

Returns :

the new SyncState object or None .

class patroni.dcs. Cluster ( * args : Any , ** kwargs : Any ) View on GitHub

Bases: Cluster

Immutable object (namedtuple) which represents PostgreSQL or MPP cluster.

Note

We are using an old-style attribute declaration here because otherwise it is not possible to override __new__ method. Without it the workers by default gets always the same dict object that could be mutated.

Consists of the following fields:

Variables :

• initialize – shows whether this cluster has initialization key stored in DC or not.

• config – global dynamic configuration, reference to ClusterConfig object.

• leader – Leader object which represents current leader of the cluster.

• status – Status object which represents the /status key.

• members – list of:class:` Member` objects, all PostgreSQL cluster members including leader

• failover – reference to Failover object.

• sync – reference to SyncState object, last observed synchronous replication state.

• history – reference to TimelineHistory object.

• failsafe – failsafe topology. Node is allowed to become the leader only if its name is found in this list.

• workers – dictionary of workers of the MPP cluster, optional. Each key representing the group and the corresponding value is a Cluster instance.

property __permanent_logical_slots : Dict [ str , Any ]

Dictionary of permanent logical replication slots.

property __permanent_slots : Dict [ str , Dict [ str , Any ] | Any ]

Dictionary of permanent replication slots with their known LSN.

_get_members_slots ( name : str , role : str , nofailover : bool , can_advance_slots : bool ) → Dict [ str , Dict [ str , Any ] ] View on GitHub

Get physical replication slots configuration for a given member.

There are following situations possible:

• If the nostream tag is set on the member - we should not have the replication slot for it on the current primary or any other member even if replicatefrom is set, because nostream disables WAL streaming.

• PostgreSQL is 11 and newer and configuration allows retention of member replication slots. In this case we want to have replication slots for every member except the case when we have nofailover tag set.

• PostgreSQL is older than 11 or configuration doesn’t allow member slots retention. In this case we want:

  • On primary have replication slots for all members that don’t have replicatefrom tag pointing to the existing member.

  • On replica node have replication slots only for members which replicatefrom tag pointing to us.

Will log an error if:

• Conflicting slot names between members are found

Parameters :

• name – name of this node.

• role – role of this node, primary , standby_leader , or replica .

• nofailover – True if this node is tagged to not be a failover candidate, False otherwise.

• can_advance_slots – True if pg_replication_slot_advance() function is available, False otherwise.

Returns :

dictionary of physical replication slots that should exist on a given node.

_get_permanent_slots ( postgresql : Postgresql , tags : Tags , role : str ) → Dict [ str , Any ] View on GitHub

Get configured permanent replication slots.

Note

Permanent replication slots are only considered if use_slots configuration is enabled. A node that is not supposed to become a leader ( nofailover ) will not have permanent replication slots. Also node with disabled streaming ( nostream ) and its cascading followers must not have permanent logical slots due to lack of feedback from node to primary, which makes them unsafe to use.

In a standby cluster we only support physical replication slots.

The returned dictionary for a non-standby cluster always contains permanent logical replication slots in order to show a warning if they are not supported by PostgreSQL before v11.

Parameters :

• postgresql – reference to Postgresql object.

• tags – reference to an object implementing Tags interface.

• role – role of the node – primary , standby_leader or replica .

Returns :

dictionary of permanent slot names mapped to attributes.

_has_permanent_logical_slots ( postgresql : Postgresql , member : Tags ) → bool View on GitHub

Check if the given member node has permanent logical replication slots configured.

Parameters :

• postgresql – reference to a Postgresql object.

• member – reference to an object implementing Tags interface for the node that we are checking permanent logical replication slots for.

Returns :

True if any detected replications slots are logical , otherwise False .

_merge_permanent_slots ( slots : Dict [ str , Dict [ str , Any ] ] , permanent_slots : Dict [ str , Any ] , name : str , role : str , can_advance_slots : bool ) → List [ str ] View on GitHub

Merge replication slots for members with permanent_slots .

Perform validation of configured permanent slot name, skipping invalid names.

Will update slots in-line based on type of slot, physical or logical , and name of node. Type is assumed to be physical if there are no attributes stored as the slot value.

Parameters :

• slots – Slot names with existing attributes if known.

• name – name of this node.

• role – role of the node – primary , standby_leader or replica .

• permanent_slots – dictionary containing slot name key and slot information values.

• can_advance_slots – True if pg_replication_slot_advance() function is available, False otherwise.

Returns :

List of disabled permanent, logical slot names, if postgresql version < 11.

static empty ( ) → Cluster View on GitHub

Produce an empty Cluster instance.

get_clone_member ( exclude_name : str ) → Member | Leader | None View on GitHub

Get member or leader object to use as clone source.

Parameters :

exclude_name – name of a member name to exclude.

Returns :

a randomly selected candidate member from available running members that are configured to as viable sources for cloning (has tag clonefrom in configuration). If no member is appropriate the current leader is used.

get_member ( member_name : str , fallback_to_leader : bool = True ) → Member | Leader | None View on GitHub

Get Member object by name or the Leader .

Parameters :

• member_name – name of the member to retrieve.

• fallback_to_leader – if True return the Leader instead if the member cannot be found.

Returns :

the Member if found or Leader object.

get_replication_slots ( postgresql : Postgresql , member : Tags , * , role : str | None = None , show_error : bool = False ) → Dict [ str , Dict [ str , Any ] ] View on GitHub

Lookup configured slot names in the DCS, report issues found and merge with permanent slots.

Will log an error if:

• Any logical slots are disabled, due to version compatibility, and show_error is True .

Parameters :

• postgresql – reference to Postgresql object.

• member – reference to an object implementing Tags interface.

• role – role of the node, if not set will be taken from postgresql .

• show_error – if True report error if any disabled logical slots or conflicting slot names are found.

Returns :

final dictionary of slot names, after merging with permanent slots and performing sanity checks.

get_slot_name_on_primary ( name : str , tags : Tags ) → str | None View on GitHub

Get the name of physical replication slot for this node on the primary.

Note

P <– I <– L

In case of cascading replication we have to check not our physical slot, but slot of the replica that connects us to the primary.

Parameters :

• name – name of the member node to check.

• tags – reference to an object implementing Tags interface.

Returns :

the slot name on the primary that is in use for physical replication on this node.

has_member ( member_name : str ) → bool View on GitHub

Check if the given member name is present in the cluster.

Parameters :

member_name – name to look up in the members .

Returns :

True if the member name is found.

has_permanent_slots ( postgresql : Postgresql , member : Tags ) → bool View on GitHub

Check if our node has permanent replication slots configured.

Parameters :

• postgresql – reference to Postgresql object.

• member – reference to an object implementing Tags interface for the node that we are checking permanent logical replication slots for.

Returns :

True if there are permanent replication slots configured, otherwise False .

is_empty ( ) View on GitHub

Validate definition of all attributes of this Cluster instance.

Returns :

True if all attributes of the current Cluster are unpopulated.

static is_logical_slot ( value : Any ) → bool View on GitHub

Check whether provided configuration is for permanent logical replication slot.

Parameters :

value – configuration of the permanent replication slot.

Returns :

True if value is a logical replication slot, otherwise False .

static is_physical_slot ( value : Any ) → bool View on GitHub

Check whether provided configuration is for permanent physical replication slot.

Parameters :

value – configuration of the permanent replication slot.

Returns :

True if value is a physical replication slot, otherwise False .

is_unlocked ( ) → bool View on GitHub

Check if the cluster does not have the leader.

Returns :

True if a leader name is not defined.

property leader_name : str | None View on GitHub

The name of the leader if defined otherwise None .

maybe_filter_permanent_slots ( postgresql : Postgresql , slots : Dict [ str , int ] ) → Dict [ str , int ] View on GitHub

Filter out all non-permanent slots from provided slots dict.

Note

In case if retention of replication slots for members is enabled we will not do any filtering, because we need to publish LSN values for members replication slots, so that other nodes can use them to advance LSN, like they do it for permanent slots.

Parameters :

• postgresql – reference to Postgresql object.

• slots – slot names with LSN values.

Returns :

a dict object that contains only slots that are known to be permanent.

property min_version : Tuple [ int , ... ] | None View on GitHub

Lowest Patroni software version found in known members of the cluster.

property permanent_physical_slots : Dict [ str , Any ] View on GitHub

Dictionary of permanent physical replication slots.

should_enforce_hot_standby_feedback ( postgresql : Postgresql , member : Tags ) → bool View on GitHub

Determine whether hot_standby_feedback should be enabled for the given member.

The hot_standby_feedback must be enabled if the current replica has logical slots, or it is working as a cascading replica for the other node that has logical slots.

Parameters :

• postgresql – reference to a Postgresql object.

• member – reference to an object implementing Tags interface for the node that we are checking permanent logical replication slots for.

Returns :

True if this node or any member replicating from this node has permanent logical slots, otherwise False .

property slots : Dict [ str , int ] View on GitHub

{"slot_name": int} .

Note

We are trying to be foolproof here and for values that can’t be parsed to int will return 0 .

Type :

State of permanent replication slots on the primary in the format

property timeline : int View on GitHub

Get the cluster history index from the history .

Returns :

If the recorded history is empty assume timeline is 1 , if it is not defined or the stored history is not formatted as expected 0 is returned and an error will be logged. Otherwise, the last number stored incremented by 1 is returned.

Example :

No history provided: >>> Cluster(0, 0, 0, Status.empty(), 0, 0, 0, 0, None, {}).timeline 0

Empty history assume timeline is 1 : >>> Cluster(0, 0, 0, Status.empty(), 0, 0, 0, TimelineHistory.from_node(1, ‘[]’), None, {}).timeline 1

Invalid history format, a string of a , returns 0 : >>> Cluster(0, 0, 0, Status.empty(), 0, 0, 0, TimelineHistory.from_node(1, ‘[["a"]]’), None, {}).timeline 0

History as a list of strings: >>> history = TimelineHistory.from_node(1, ‘[["3", "2", "1"]]’) >>> Cluster(0, 0, 0, Status.empty(), 0, 0, 0, history, None, {}).timeline 4

class patroni.dcs. ClusterConfig ( version : int | str , data : Dict [ str , Any ] , modify_version : int | str ) View on GitHub

Bases: NamedTuple

Immutable object (namedtuple) which represents cluster configuration.

Variables :

• version – version number for the object.

• data – dictionary of configuration information.

• modify_version – modified version number.

_asdict ( )

Return a new dict which maps field names to their values.

_field_defaults = {}

_fields = ('version', 'data', 'modify_version')

classmethod _make ( iterable )

Make a new ClusterConfig object from a sequence or iterable

_replace ( ** kwds )

Return a new ClusterConfig object replacing specified fields with new values

data : Dict [ str , Any ]

Alias for field number 1

static from_node ( version : int | str , value : str , modify_version : str | int | None = None ) → ClusterConfig View on GitHub

Factory method to parse value as configuration information.

Parameters :

• version – version number for object.

• value – raw JSON serialized data, if not parsable replaced with an empty dictionary.

• modify_version – optional modify version number, use version if not provided.

Returns :

constructed ClusterConfig instance.

Example :

>>> ClusterConfig.from_node(1, '{') is None
False

modify_version : int | str

Alias for field number 2

version : int | str

Alias for field number 0

class patroni.dcs. Failover ( version : int | str , leader : str | None , candidate : str | None , scheduled_at : datetime | None ) View on GitHub

Bases: NamedTuple

Immutable object (namedtuple) representing configuration information required for failover/switchover capability.

Variables :

• version – version of the object.

• leader – name of the leader. If value isn’t empty we treat it as a switchover from the specified node.

• candidate – the name of the member node to be considered as a failover candidate.

• scheduled_at – in the case of a switchover the datetime object to perform the scheduled switchover.

Example :

>>> 'Failover' in str(Failover.from_node(1, '{"leader": "cluster_leader"}'))
True

>>> 'Failover' in str(Failover.from_node(1, {"leader": "cluster_leader"}))
True

>>> 'Failover' in str(Failover.from_node(1, '{"leader": "cluster_leader", "member": "cluster_candidate"}'))
True

>>> Failover.from_node(1, 'null') is None
False

>>> n = '''{"leader": "cluster_leader", "member": "cluster_candidate",
...         "scheduled_at": "2016-01-14T10:09:57.1394Z"}'''

>>> 'tzinfo=' in str(Failover.from_node(1, n))
True

>>> Failover.from_node(1, None) is None
False

>>> Failover.from_node(1, '{}') is None
False

>>> 'abc' in Failover.from_node(1, 'abc:def')
True

_asdict ( )

Return a new dict which maps field names to their values.

_field_defaults = {}

_fields = ('version', 'leader', 'candidate', 'scheduled_at')

classmethod _make ( iterable )

Make a new Failover object from a sequence or iterable

_replace ( ** kwds )

Return a new Failover object replacing specified fields with new values

candidate : str | None

Alias for field number 2

static from_node ( version : int | str , value : str | Dict [ str , str ] ) → Failover View on GitHub

Factory method to parse value as failover configuration.

Parameters :

• version – version number for the object.

• value – JSON serialized data or a dictionary of configuration. Can also be a colon : delimited list of leader, followed by candidate name (legacy format). If scheduled_at key is defined the value will be parsed by dateutil.parser.parse() .

Returns :

constructed Failover information object

leader : str | None

Alias for field number 1

scheduled_at : datetime | None

Alias for field number 3

version : int | str

Alias for field number 0

class patroni.dcs. Leader ( version : int | str , session : int | float | str | None , member : Member ) View on GitHub

Bases: NamedTuple

Immutable object (namedtuple) which represents leader key.

Consists of the following fields:

Variables :

• version – modification version of a leader key in a Configuration Store

• session – either session id or just ttl in seconds

• member – reference to a Member object which represents current leader (see Cluster.members )

_asdict ( )

Return a new dict which maps field names to their values.

_field_defaults = {}

_fields = ('version', 'session', 'member')

classmethod _make ( iterable )

Make a new Leader object from a sequence or iterable

_replace ( ** kwds )

Return a new Leader object replacing specified fields with new values

property checkpoint_after_promote : bool | None View on GitHub

Determine whether a checkpoint has occurred for this leader after promotion.

Returns :

True if the role is master or primary and checkpoint_after_promote is not set, False if not a master or primary or if the checkpoint hasn’t occurred. If the version of Patroni is older than 1.5.6, return None .

Example :

>>> Leader(1, '', Member.from_node(1, '', '', '{"version":"z"}')).checkpoint_after_promote

conn_kwargs ( auth : Dict [ str , str ] | None = None ) → Dict [ str , str ] View on GitHub

Connection keyword arguments.

Parameters :

auth – an optional dictionary containing authentication information.

Returns :

the result of the called Member.conn_kwargs() method.

property conn_url : str | None View on GitHub

Connection URL value of the Member instance.

property data : Dict [ str , Any ] View on GitHub

Data value of the Member instance.

member : Member

Alias for field number 2

property name : str View on GitHub

The leader "member" name.

session : int | float | str | None

Alias for field number 1

property timeline : int | None View on GitHub

Timeline value of data .

version : int | str

Alias for field number 0