ASF GitHub Bot logged work on BEAM-8537:

                Author: ASF GitHub Bot
            Created on: 14/Feb/20 02:44
            Start Date: 14/Feb/20 02:44
    Worklog Time Spent: 10m 
      Work Description: boyuanzz commented on pull request #10375: [BEAM-8537] 
Provide WatermarkEstimator to track watermark
URL: https://github.com/apache/beam/pull/10375#discussion_r379226640

 File path: sdks/python/apache_beam/io/watermark_estimators.py
 @@ -0,0 +1,101 @@
+# 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,
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""A collection of WatermarkEstimator implementations that SplittableDoFns
+can use."""
+# pytype: skip-file
+from __future__ import absolute_import
+from apache_beam.io.iobase import WatermarkEstimator
+from apache_beam.utils.timestamp import Timestamp
+class MonotonicWatermarkEstimator(WatermarkEstimator):
+  """A WatermarkEstimator which assumes that timestamps of all ouput records
+  are increasing monotonically.
+  """
+  def __init__(self, timestamp):
+    """For a new <element, restriction> pair, the initial value is None. When
+    resuming processing, the initial timestamp will be the last reported
+    watermark.
+    """
+    self._watermark = timestamp
+  def observe_timestamp(self, timestamp):
+    if self._watermark is None:
+      self._watermark = timestamp
+    else:
+      if timestamp < self._watermark:
+        raise ValueError('A MonotonicWatermarkEstimator expects output '
+                         'timestamp to be increasing monotonically.')
+      self._watermark = timestamp
+  def current_watermark(self):
+    return self._watermark
+  def get_estimator_state(self):
+    return self._watermark
+class WalltimeWatermarkEstimator(WatermarkEstimator):
+  """A WatermarkEstimator which uses processing time as the estimated 
+  """
+  def __init__(self, timestamp=None):
+    if timestamp:
 Review comment:
   Done. Thanks!
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Issue Time Tracking

    Worklog Id:     (was: 387068)
    Time Spent: 15h 40m  (was: 15.5h)

> Provide WatermarkEstimatorProvider for different types of WatermarkEstimator
> ----------------------------------------------------------------------------
>                 Key: BEAM-8537
>                 URL: https://issues.apache.org/jira/browse/BEAM-8537
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-py-core, sdk-py-harness
>            Reporter: Boyuan Zhang
>            Assignee: Boyuan Zhang
>            Priority: Major
>          Time Spent: 15h 40m
>  Remaining Estimate: 0h
> This is a follow up for in-progress PR:  
> https://github.com/apache/beam/pull/9794.
> Current implementation in PR9794 provides a default implementation of 
> WatermarkEstimator. For further work, we want to let WatermarkEstimator to be 
> a pure Interface. We'll provide a WatermarkEstimatorProvider to be able to 
> create a custom WatermarkEstimator per windowed value. It should be similar 
> to how we track restriction for SDF: 
> WatermarkEstimator <---> RestrictionTracker 
> WatermarkEstimatorProvider <---> RestrictionTrackerProvider
> WatermarkEstimatorParam <---> RestrictionDoFnParam

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