patroni.postgresql.sync module
- class patroni.postgresql.sync.SyncHandler(postgresql: Postgresql)View on GitHub
Bases:
object
Class responsible for working with the synchronous_standby_names.
Sync standbys are chosen based on their state in pg_stat_replication. When synchronous_standby_names is changed we memorize the _primary_flush_lsn and the current_state() method will count newly added names as “sync” only when they reached memorized LSN and also reported as “sync” by pg_stat_replication
- __init__(postgresql: Postgresql) None View on GitHub
- _handle_synchronous_standby_names_change() None View on GitHub
Handles changes of “synchronous_standby_names” GUC.
If “synchronous_standby_names” was changed, we need to check that newly added replicas have reached self._primary_flush_lsn. Only after that they could be counted as synchronous.
- _process_replica_readiness(cluster: Cluster, replica_list: _ReplicaList) None View on GitHub
Flags replicas as truly “synchronous” when they have caught up with
_primary_flush_lsn
.- Parameters:
cluster – current cluster topology from DCS
replica_list – collection of replicas that we want to evaluate.
- current_state(cluster: Cluster) Tuple[CaseInsensitiveSet, CaseInsensitiveSet] View on GitHub
Find the best candidates to be the synchronous standbys.
Current synchronous standby is always preferred, unless it has disconnected or does not want to be a synchronous standby any longer.
Standbys are selected based on values from the global configuration:
maximum_lag_on_syncnode: would help swapping unhealthy sync replica in case if it stops responding (or hung). Please set the value high enough so it won’t unncessarily swap sync standbys during high loads. Any value less or equal of 0 keeps the behavior backward compatible. Please note that it will not also swap sync standbys in case where all replicas are hung.
synchronous_node_count: controlls how many nodes should be set as synchronous.
- Returns:
tuple of candidates
CaseInsensitiveSet
and synchronous standbysCaseInsensitiveSet
.
- set_synchronous_standby_names(sync: Collection[str]) None View on GitHub
Constructs and sets “synchronous_standby_names” GUC value.
- Parameters:
sync – set of nodes to sync to
- class patroni.postgresql.sync._Replica(pid: int, application_name: str, sync_state: str, lsn: int, nofailover: bool)View on GitHub
Bases:
NamedTuple
Class representing a single replica that is eligible to be synchronous.
Attributes are taken from
pg_stat_replication
view and respectiveCluster.members
.- Variables:
pid – PID of walsender process.
application_name – matches with the
Member.name
.sync_state – possible values are:
async
,potential
,quorum
, andsync
.lsn –
write_lsn
,flush_lsn
, orreplay_lsn
, depending on the value ofsynchronous_commit
GUC.nofailover – whether the corresponding member has
nofailover
tag set toTrue
.
- _asdict()View on GitHub
Return a new dict which maps field names to their values.
- _field_defaults = {}
- _fields = ('pid', 'application_name', 'sync_state', 'lsn', 'nofailover')
- classmethod _make(iterable)View on GitHub
Make a new _Replica object from a sequence or iterable
- _replace(**kwds)View on GitHub
Return a new _Replica object replacing specified fields with new values
- class patroni.postgresql.sync._ReplicaList(postgresql: Postgresql, cluster: Cluster)View on GitHub
-
A collection of :class:
_Replica
objects.Values are reverse ordered by
_Replica.sync_state
and_Replica.lsn
. That is, first there will be replicas that havesync_state
==sync
, even if they are not the most up-to-date in term of write/flush/replay LSN. It helps to keep the result of chosing new synchronous nodes consistent in case if a synchronous standby member is slowed down OR async node is receiving changes faster than the sync member. Such cases would trigger sync standby member swapping, but only if lag on this member is exceeding a threshold (maximum_lag_on_syncnode
).- Variables:
max_lsn – maximum value of
_Replica.lsn
among all values. In case if there is just one element in the list we take value ofpg_current_wal_flush_lsn()
.
- __init__(postgresql: Postgresql, cluster: Cluster) None View on GitHub
Create :class:
_ReplicaList
object.- Parameters:
postgresql – reference to :class:
Postgresql
object.cluster – currently known cluster state from DCS.
- class patroni.postgresql.sync._SSN(sync_type: str, has_star: bool, num: int, members: CaseInsensitiveSet)View on GitHub
Bases:
NamedTuple
class representing “synchronous_standby_names” value after parsing.
- Variables:
sync_type – possible values: ‘off’, ‘priority’, ‘quorum’
has_star – is set to True if “synchronous_standby_names” contains ‘*’
num – how many nodes are required to be synchronous
members – collection of standby names listed in “synchronous_standby_names”
- _asdict()View on GitHub
Return a new dict which maps field names to their values.
- _field_defaults = {}
- _fields = ('sync_type', 'has_star', 'num', 'members')
- classmethod _make(iterable)View on GitHub
Make a new _SSN object from a sequence or iterable
- _replace(**kwds)View on GitHub
Return a new _SSN object replacing specified fields with new values
- members: CaseInsensitiveSet
Alias for field number 3
- patroni.postgresql.sync.parse_sync_standby_names(value: str) _SSN View on GitHub
Parse postgresql synchronous_standby_names to constituent parts.
- Parameters:
value – the value of synchronous_standby_names
- Returns:
_SSN
object- Raises:
ValueError – if the configuration value can not be parsed
>>> parse_sync_standby_names('').sync_type 'off'
>>> parse_sync_standby_names('FiRsT').sync_type 'priority'
>>> 'first' in parse_sync_standby_names('FiRsT').members True
>>> set(parse_sync_standby_names('"1"').members) {'1'}
>>> parse_sync_standby_names(' a , b ').members == {'a', 'b'} True
>>> parse_sync_standby_names(' a , b ').num 1
>>> parse_sync_standby_names('ANY 4("a",*,b)').has_star True
>>> parse_sync_standby_names('ANY 4("a",*,b)').num 4
>>> parse_sync_standby_names('1') Traceback (most recent call last): ... ValueError: Unparseable synchronous_standby_names value
>>> parse_sync_standby_names('a,') Traceback (most recent call last): ... ValueError: Unparseable synchronous_standby_names value
>>> parse_sync_standby_names('ANY 4("a" b,"c c")') Traceback (most recent call last): ... ValueError: Unparseable synchronous_standby_names value
>>> parse_sync_standby_names('FIRST 4("a",)') Traceback (most recent call last): ... ValueError: Unparseable synchronous_standby_names value
>>> parse_sync_standby_names('2 (,)') Traceback (most recent call last): ... ValueError: Unparseable synchronous_standby_names value
- patroni.postgresql.sync.quote_ident(value: str) str View on GitHub
Very simplified version of psycopg
quote_ident()
function.