dianfu commented on a change in pull request #8681: [FLINK-12585][python] Align Stream/BatchTableEnvironment with JAVA Table API URL: https://github.com/apache/flink/pull/8681#discussion_r292254893
########## File path: flink-python/pyflink/common/checkpointing_mode.py ########## @@ -0,0 +1,105 @@ +################################################################################ +# Licensed to the Apache Software Foundation (ASF) under one +# or more contributor license agreements. See the NOTICE file +# distributed with this work for additional information +# regarding copyright ownership. The ASF licenses this file +# to you under the Apache License, Version 2.0 (the +# "License"); you may not use this file except in compliance +# with the License. You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. +################################################################################ +from pyflink.java_gateway import get_gateway + +__all__ = ['CheckpointingMode'] + + +class CheckpointingMode(object): + """ + The checkpointing mode defines what consistency guarantees the system gives in the presence of + failures. + + When checkpointing is activated, the data streams are replayed such that lost parts of the + processing are repeated. For stateful operations and functions, the checkpointing mode defines + whether the system draws checkpoints such that a recovery behaves as if the operators/functions + see each record "exactly once" (:data:`CheckpointingMode.EXACTLY_ONCE`), or whether the + checkpoints are drawn in a simpler fashion that typically encounters some duplicates upon + recovery (:data:`CheckpointingMode.AT_LEAST_ONCE`) + + :data:`EXACTLY_ONCE`: + + Sets the checkpointing mode to "exactly once". This mode means that the system will + checkpoint the operator and user function state in such a way that, upon recovery, + every record will be reflected exactly once in the operator state. + + For example, if a user function counts the number of elements in a stream, + this number will consistently be equal to the number of actual elements in the stream, + regardless of failures and recovery. + + Note that this does not mean that each record flows through the streaming data flow + only once. It means that upon recovery, the state of operators/functions is restored such + that the resumed data streams pick up exactly at after the last modification to the state. + + Note that this mode does not guarantee exactly-once behavior in the interaction with + external systems (only state in Flink's operators and user functions). The reason for that + is that a certain level of "collaboration" is required between two systems to achieve + exactly-once guarantees. However, for certain systems, connectors can be written that + facilitate this collaboration. + + This mode sustains high throughput. Depending on the data flow graph and operations, + this mode may increase the record latency, because operators need to align their input + streams, in order to create a consistent snapshot point. The latency increase for simple + dataflows (no repartitioning) is negligible. For simple dataflows with repartitioning, the + average latency remains small, but the slowest records typically have an increased latency. + + :data:`AT_LEAST_ONCE`: + + Sets the checkpointing mode to "at least once". This mode means that the system will + checkpoint the operator and user function state in a simpler way. Upon failure and recovery, + some records may be reflected multiple times in the operator state. + + For example, if a user function counts the number of elements in a stream, + this number will equal to, or larger, than the actual number of elements in the stream, + in the presence of failure and recovery. + + This mode has minimal impact on latency and may be preferable in very-low latency + scenarios, where a sustained very-low latency (such as few milliseconds) is needed, + and where occasional duplicate messages (on recovery) do not matter. + """ + + EXACTLY_ONCE = 0 + AT_LEAST_ONCE = 1 + + @classmethod + def _from_j_checkpointing_mode(cls, j_checkpointing_mode): + gateway = get_gateway() + JCheckpointingMode = \ + gateway.jvm.org.apache.flink.streaming.api.CheckpointingMode + if j_checkpointing_mode == JCheckpointingMode.EXACTLY_ONCE: + return CheckpointingMode.EXACTLY_ONCE + elif j_checkpointing_mode == JCheckpointingMode.AT_LEAST_ONCE: + return CheckpointingMode.AT_LEAST_ONCE + elif j_checkpointing_mode is None: Review comment: In which case j_checkpointing_mode will be None? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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