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Move _node_hash to PgDistNode and call it as_tuple.

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And more work on docstrings
This commit is contained in:
Alexander Kukushkin
2023-08-24 12:09:06 +02:00
parent e96b77c7aa
commit c4f95200bc
1 changed files with 38 additions and 38 deletions
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patroni/postgresql/citus.py
+38 -38
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@@ -22,9 +22,9 @@ class PgDistNode:
.. note::
Unlike "noderole" possible values of ``role`` are 'primary', 'secondary', and 'demoted'.
Unlike "noderole" possible values of ``role`` are ``primary``, ``secondary``, and ``demoted``.
The last one is used to pause client connections on the coordinator to the worker by
appending '-demoted' suffix to the "nodename". The actual "noderole" in DB remains 'primary'.
appending ``-demoted`` suffix to the "nodename". The actual "noderole" in DB remains ``primary``.
:ivar host: "nodename" value
:ivar port: "nodeport" value
@@ -48,15 +48,16 @@ class PgDistNode:
def __hash__(self) -> int:
"""Defines a hash function to put :class:`PgDistNode` objects to :class:`PgDistGroup` set-like object.
We use (*host*, *port*) tuple here because it is one of the UNIQUE constraints on the "pg_dist_node" table.
The *role* value is irrelevant here because nodes may change their roles.
.. note::
We use (:attr:`host`, :attr:`port`) tuple here because it is one of the UNIQUE constraints on the
"pg_dist_node" table. The :attr:`role` value is irrelevant here because nodes may change their roles.
"""
return hash((self.host, self.port))
def __eq__(self, other: Any) -> bool:
"""Defines a comparison function.
:returns: ``True`` if *host* and *port* between two instances are the same.
:returns: ``True`` if :attr:`host` and :attr:`port` between two instances are the same.
"""
return isinstance(other, PgDistNode) and self.host == other.host and self.port == other.port
@@ -70,10 +71,23 @@ class PgDistNode:
def is_primary(self) -> bool:
"""Checks whether this object represents "primary" in a corresponding group.
:returns: ``True`` if this object represents "primary".
:returns: ``True`` if this object represents the ``primary``.
"""
return self.role in ('primary', 'demoted')
def as_tuple(self, include_nodeid: bool = False) -> Tuple[str, int, str, Optional[int]]:
"""Helper method to compare two :class:`PgDistGroup` objects.
.. note::
*include_nodeid* is set to ``True`` only in unit-tests.
:param include_nodeid: whether :attr:`nodeid` should be taken into account when comparison is performed.
:returns: :class:`tuple` object with :attr:`host`, :attr:`port`, :attr:`role`, and optionally :attr:`nodeid`.
"""
return self.host, self.port, self.role, (self.nodeid if include_nodeid else None)
class PgDistGroup(Set[PgDistNode]):
"""A :class:`set`-like object that represents a Citus group in "pg_dist_node" table.
@@ -104,48 +118,34 @@ class PgDistGroup(Set[PgDistNode]):
if nodes:
self.update(nodes)
@staticmethod
def _node_hash(node: PgDistNode, include_nodeid: bool = False) -> Tuple[str, int, str, Optional[int]]:
"""Helper function to compare two :class:`PgDistGroup` objects.
.. note::
*include_nodeid* is set to ``True`` only in unit-tests.
:param node: the PgDistNode we want to build hash for.
:param include_nodeid: whether *nodeid* should be taken into account when comparison is performed.
:returns: :class:`tuple` object with *host*, *port*, *role*, and optionally *nodeid*
"""
return node.host, node.port, node.role, (node.nodeid if include_nodeid else None)
def equals(self, other: 'PgDistGroup', check_nodeid: bool = False) -> bool:
"""Compares two :class:`PgDistGroup` objects.
.. note::
Normally only *host*, *port*, and *role* values are compared for all :class:`PgDistNode` objects.
But, optionally it can also compare *nodeid* if *check_nodeid* if set to ``True`` (used only in unit-tests).
:param other: what we want to compare with.
:param check_nodeid: whether *nodeid* should be compared in addition to *host*, *port*, and *role*.
:returns: ``True`` if all two objects are identical.
:param check_nodeid: whether :attr:`PgDistNode.nodeid` should be compared in addition to
:attr:`PgDistNode.host`, :attr:`PgDistNode.port`, and :attr:`PgDistNode.role`.
:returns: ``True`` if two :class:`PgDistGroup` objects are fully identical.
"""
return set(self._node_hash(v, check_nodeid) for v in self)\
== set(self._node_hash(v, check_nodeid) for v in other)
return self.groupid == other.groupid\
and set(v.as_tuple(check_nodeid) for v in self) == set(v.as_tuple(check_nodeid) for v in other)
def primary(self) -> Optional[PgDistNode]:
"""Finds and returns :class:`PgDistNode` object that represents "primary"."""
"""Finds and returns :class:`PgDistNode` object that represents the "primary".
:returns: :class:`PgDistNode` object which represents the "primary" or ``None`` if not found.
"""
return next(iter(v for v in self if v.is_primary()), None)
def get(self, value: PgDistNode) -> Optional[PgDistNode]:
"""Performs a lookup of the actual value in a given set.
"""Performs a lookup of the actual value in a set.
.. note::
It is necessary because :func:`__hash__` and :func:`__eq__` methods in :class:`PgDistNode`
are redefined and effectively they check only *host* and *port* attributes.
It is necessary because :func:`__hash__` and :func:`__eq__` methods in :class:`PgDistNode` are
redefined and effectively they check only :attr:`PgDistNode.host` and :attr:`PgDistNode.port` attributes.
:param value: the key we search for.
:returns: the actual :class:`PgDistNode`` value from this :class:`PgDistGroup` object or ``None``.
:returns: the actual :class:`PgDistNode` value from this :class:`PgDistGroup` object or ``None`` if not found.
"""
return next(iter(v for v in self if v == value), None)
@@ -156,7 +156,7 @@ class PgDistGroup(Set[PgDistNode]):
The actual yielded object is :class:`PgDistNode` that will be passed to
the :meth:`CitusHandler.update_node` to execute all transitions in a transaction.
In addition to the yielding transactions this method fills up *nodeid*
In addition to the yielding transactions this method fills up :attr:`PgDistNode.nodeid`
attribute for nodes that are presented in the old and in the new topology.
There are a few simple rules/constraints that are imposed by Citus and must be followed:
@@ -167,9 +167,9 @@ class PgDistGroup(Set[PgDistNode]):
- "nodename", "nodeport" must be unique across all rows in the "pg_dist_node". This means that
every time we want to change the nodeid of an existing node (i.e. to change it from secondary
to primary), we should first write some other "nodename"/"port" to the row it's currently in.
to primary), we should first write some other "nodename"/"nodeport" to the row it's currently in.
- updating "broken" nodes always works and metadata is synced asynchnonously after commit.
- updating "broken" nodes always works and metadata is synced asynchnonously after the commit.
Following these rules below is an example of the switchover between node1 (primary, nodeid=4)
and node2 (secondary, nodeid=5).
@@ -182,7 +182,7 @@ class PgDistGroup(Set[PgDistNode]):
SELECT citus_update_node(4, 'node2', 5432);
COMMIT;
:param old: the last known topology registered in "pg_dist_node" for a given *groupid*
:param old: the last known topology registered in "pg_dist_node" for a given :attr:`groupid`.
:yields: :class:`PgDistNode` objects that must be updated/added/removed in "pg_dist_node".
"""