def get_metric(self, metric_name):
"""See bg_accessor.Accessor."""
super(_CassandraAccessor, self).get_metric(metric_name)
metric_name = bg_accessor.encode_metric_name(metric_name)
result = list(self.__session.execute(
self.__select_metric_statement, (metric_name, )))
if not result:
return None
config = result[0][0]
return bg_accessor.Metric(
metric_name, bg_accessor.MetricMetadata.from_string_dict(config))
def _cache_set(self, metric_name, metric):
"""If metric is valid, add it to the cache.
The metric is stored in the cache as follows:
- its id, which is a UUID.
- vertical bar (pipe) separator.
- its metadata JSON representation.
"""
encoded_metric_name = bg_accessor.encode_metric_name(metric_name)
key = encoded_metric_name
value = self.__value_from_metric(metric)
with self.__env.begin(self.__metric_to_metadata_db, write=True) as txn:
txn.put(key, value, dupdata=False, overwrite=True)
def make_metric(name, metadata=None, **kwargs):
"""Create a bg_accessor.Metric with specified metadata."""
encoded_name = bg_accessor.encode_metric_name(name)
id = uuid.uuid5(_UUID_NAMESPACE, encoded_name)
retention = kwargs.get("retention")
if isinstance(retention, basestring):
kwargs["retention"] = bg_accessor.Retention.from_string(retention)
if metadata:
assert isinstance(metadata, bg_accessor.MetricMetadata)
assert not kwargs
else:
metadata = bg_accessor.MetricMetadata(**kwargs)
return bg_accessor.Metric(name, id, metadata)
def make_metric(name, metadata=None, accessor=None, **kwargs):
"""Create a bg_accessor.Metric with specified metadata."""
encoded_name = bg_accessor.encode_metric_name(name)
retention = kwargs.get("retention")
if isinstance(retention, basestring):
kwargs["retention"] = bg_accessor.Retention.from_string(retention)
if metadata:
assert isinstance(metadata, bg_accessor.MetricMetadata)
assert not kwargs
else:
metadata = bg_accessor.MetricMetadata(**kwargs)
if not accessor:
uid = uuid.uuid5(_UUID_NAMESPACE, encoded_name)
return bg_accessor.Metric(name, uid, metadata)
else:
return accessor.make_metric(name, metadata)
def _cache_get(self, metric_name):
"""Return a Metric from a the cache, None if no such metric."""
encoded_metric_name = bg_accessor.encode_metric_name(metric_name)
with self.__env.begin(self.__metric_to_metadata_db, write=False) as txn:
payload = txn.get(encoded_metric_name)
if payload == self._EMPTY:
return None, True
if not payload:
# cache miss
return None, False
# found something in the cache
split = self.__split_payload(payload)
if split is None:
# invalid string => evict from cache
with self.__env.begin(self.__metric_to_metadata_db, write=True) as txn:
txn.delete(key=encoded_metric_name)
return None, False
# valid value => get id and metadata string
# TODO: optimization: id is a UUID (known length)
id_str, metadata_str, timestamp = split
try:
id = uuid.UUID(id_str)
except Exception as e:
logging.debug(str(e))
with self.__env.begin(self.__metric_to_metadata_db, write=True) as txn:
txn.delete(key=encoded_metric_name)
return None, False
# if the timestamp expired evict it in order to force
# its recreation for the next time
if self.__expired_timestamp(timestamp):
with self.__env.begin(self.__metric_to_metadata_db, write=True) as txn:
txn.delete(key=encoded_metric_name)
metadata = self.metadata_from_str(metadata_str)
return bg_accessor.Metric(metric_name, id, metadata), True
def get_metric(self, metric_name):
"""Return a MetricMetadata for this metric_name, None if no such metric."""
metric_name = bg_accessor.encode_metric_name(metric_name)
with self.__env.begin(self.__metric_to_metadata_db, write=False) as txn:
metadata_str = txn.get(metric_name)
if metadata_str:
# on disk cache hit
self.hit_count += 1
with self.__json_cache_lock:
metadata = self.__json_cache.get(metadata_str)
if not metadata:
metadata = bg_accessor.MetricMetadata.from_json(metric_name, metadata_str)
self.__json_cache[metadata_str] = metadata
return metadata
else:
# on disk cache miss
self.miss_count += 1
with self.__accessor_lock:
metadata = self.__accessor.get_metric(metric_name)
self._cache(metadata)
return metadata
def _cache_has(self, metric_name):
"""Check if metric is cached."""
encoded_metric_name = bg_accessor.encode_metric_name(metric_name)
with self.__env.begin(self.__metric_to_metadata_db, write=False) as txn:
payload = txn.get(encoded_metric_name)
return payload is not None and payload != self._EMPTY