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Created December 28, 2021 08:13
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【Patroni源码阅读】创建replicas副本
class Bootstrap(object):
def create_replica(self, clone_member):
"""
create the replica according to the replica_method
defined by the user. this is a list, so we need to
loop through all methods the user supplies
"""
self._postgresql.set_state('creating replica')
self._postgresql.schedule_sanity_checks_after_pause()
is_remote_master = isinstance(clone_member, RemoteMember)
# get list of replica methods either from clone member or from
# the config. If there is no configuration key, or no value is
# specified, use basebackup
#
# 查询配置文件中定义的:create_replica_methods,参考:配置文件https://patroni.readthedocs.io/en/latest/replica_bootstrap.html#custom-replica-creation
# 该配置是个列表,用户如果没有定义,那么默认使用pg_basebackup创建副本
replica_methods = (clone_member.create_replica_methods if is_remote_master
else self._postgresql.create_replica_methods) or ['basebackup']
if clone_member and clone_member.conn_url:
r = clone_member.conn_kwargs(self._postgresql.config.replication)
# add the credentials to connect to the replica origin to pgpass.
# clone对象的连接串信息被写入pgpass文件
env = self._postgresql.config.write_pgpass(r)
connstring = self._postgresql.config.format_dsn(r, True)
else:
# 没有上游配置时,通过何种方式clone,此时replica_methods方法中的定义
connstring = ''
env = os.environ.copy()
# if we don't have any source, leave only replica methods that work without it
replica_methods = [r for r in replica_methods
if self._postgresql.replica_method_can_work_without_replication_connection(r)]
# go through them in priority order
ret = 1
for replica_method in replica_methods:
if self._postgresql.cancellable.is_cancelled:
break
method_config = self._postgresql.replica_method_options(replica_method)
# if the method is basebackup, then use the built-in
# 默认配置
if replica_method == "basebackup":
ret = self.basebackup(connstring, env, method_config)
if ret == 0:
logger.info("replica has been created using basebackup")
# if basebackup succeeds, exit with success
break
else:
if not self._postgresql.data_directory_empty():
# 指定 keep_data 参数时保留数据目录数据
if method_config.get('keep_data', False):
logger.info('Leaving data directory uncleaned')
else:
self._postgresql.remove_data_directory()
cmd = replica_method
# user-defined method; check for configuration
# not required, actually
if method_config:
# look to see if the user has supplied a full command path
# if not, use the method name as the command
cmd = method_config.pop('command', cmd)
# add the default parameters
# 追加自定义配置
if not method_config.get('no_params', False):
method_config.update({"scope": self._postgresql.scope,
"role": "replica",
"datadir": self._postgresql.data_dir,
"connstring": connstring})
else:
for param in ('no_params', 'no_master', 'keep_data'):
method_config.pop(param, None)
params = ["--{0}={1}".format(arg, val) for arg, val in method_config.items()]
try:
# call script with the full set of parameters
ret = self._postgresql.cancellable.call(shlex.split(cmd) + params, env=env)
# if we succeeded, stop
if ret == 0:
logger.info('replica has been created using %s', replica_method)
break
else:
logger.error('Error creating replica using method %s: %s exited with code=%s',
replica_method, cmd, ret)
except Exception:
logger.exception('Error creating replica using method %s', replica_method)
ret = 1
self._postgresql.set_state('stopped')
return ret
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