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

+

return correct type of etcd client +

+

+

+

+

Load and set relevant values from configuration. + Sets loop_wait, ttl and retry_timeout properties. +

+

Set the new value for retry_timeout. +

+

Set the new ttl value for DCS keys. +

Get current ttl value.

+

+

+

Calculate a request timeout and number of retries per single etcd node. In case if the timeout per node is too small (less than one second) we will reduce the number of nodes. For the cluster with only one node we will try to do 2 retries. For clusters with 2 nodes we will try to do 1 retry for every node. No retries for clusters with 3 or more nodes. We better rely on switching to a different node. +

+

+

+

One host might be resolved into multiple ip addresses. We will make list out of it +

Fetch list of etcd-cluster member by resolving _etcd-server._tcp. SRV record. This record should contain list of host and peer ports which could be used to run ‘GET http://{host}:{port}/members’ request (peer protocol) +

Gets list of members from Etcd cluster using API +

returns: list of clientURLs +

This method should fill up _machines_cache from scratch. It could happen only in two cases: 1. During class initialization 2. When all etcd members failed +

+

returns: request parameters +

returns: request_executor +

Get etcd cluster topology using Etcd API and put it to self._machines_cache +

+

Executes the query. +

+

Original machines method(property) of etcd.Client class raise exception when it failed to get list of etcd cluster members. This method is being called only when request failed on one of the etcd members during api_execute call. For us it’s more important to execute original request rather then get new topology of etcd cluster. So we will catch this exception and return empty list of machines. Later, during next api_execute call we will forcefully update machines_cache.
Also this method implements the same timeout-retry logic as api_execute, because the original method was retrying 2 times with the read_timeout on each node.
After the next refactoring the whole logic was moved to the _get_machines_list() method. +

+

+

+

+

This constructor should always be called with keyword arguments. Arguments are:
group should be None; reserved for future extension when a ThreadGroup class is implemented.
target is the callable object to be invoked by the run() method. Defaults to None, meaning nothing is called.
name is the thread name. By default, a unique name is constructed of the form “Thread-N” where N is a small decimal number.
args is a list or tuple of arguments for the target invocation. Defaults to ().
kwargs is a dictionary of keyword arguments for the target invocation. Defaults to \{}.
If a subclass overrides the constructor, it must make sure to invoke the base class constructor (Thread.__init\\__()) before doing anything else to the thread. +

+

+

+

+

Method representing the thread’s activity. + You may override this method in a subclass. The standard run() method invokes the callable object passed to the object’s constructor as the target argument, if any, with sequential and keyword arguments taken from the args and kwargs arguments, respectively.

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

+

return correct type of etcd client +

+

Remove leader key from DCS. + This method should remove leader key if current instance is the leader. +

+

+

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:::
  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.
+

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

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

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.
+

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

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

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

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.
+

Removes the initialize key for a cluster. +

Delete cluster from DCS. +

Delete the synchronous state from DCS. +

Race for cluster initialization. + This method should atomically create initialize key and return True, otherwise it should return False. +

+

Create or update /config key in DCS. +

Create or update /failover key. +

Set value for history in DCS. +

Set synchronous state in DCS. +

Set the new ttl value for DCS keys. +

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.
+

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.
+

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

alias of EtcdError +

+

+

returns: list of clientURLs +

returns: request parameters +

returns: request_executor