Decreasing peak memory usage for beam.TupleCombineFn.

[iindyk]

Loading and merging accumulators in batches in beam.TupleCombineFn.merge_accumulators instead of loading and merging all at once.

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Post-Commit SDK/Transform Integration Tests Status (on master branch)

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Pre-Commit Tests Status (on master branch)

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[iindyk]

R: @robertwb

[codecov]

Codecov Report

Merging #15271 (12d624b) into master (7b54b0b) will decrease coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #15271      +/-   ##
==========================================
- Coverage   83.86%   83.79%   -0.07%     
==========================================
  Files         441      440       -1     
  Lines       59724    59804      +80     
==========================================
+ Hits        50086    50115      +29     
- Misses       9638     9689      +51     

Impacted Files	Coverage Δ
sdks/python/apache_beam/transforms/combiners.py	93.71% <100.00%> (+0.11%)	⬆️
sdks/python/apache_beam/utils/interactive_utils.py	90.24% <0.00%> (-4.88%)	⬇️
...ks/python/apache_beam/runners/worker/data_plane.py	87.70% <0.00%> (-4.72%)	⬇️
...hon/apache_beam/runners/direct/test_stream_impl.py	94.02% <0.00%> (-2.24%)	⬇️
sdks/python/apache_beam/io/source_test_utils.py	88.47% <0.00%> (-1.39%)	⬇️
sdks/python/apache_beam/internal/metrics/metric.py	90.42% <0.00%> (-1.07%)	⬇️
...pache_beam/runners/interactive/interactive_beam.py	75.53% <0.00%> (-1.07%)	⬇️
...runners/interactive/display/pcoll_visualization.py	85.26% <0.00%> (-0.53%)	⬇️
...eam/runners/interactive/interactive_environment.py	90.33% <0.00%> (-0.38%)	⬇️
...hon/apache_beam/runners/worker/bundle_processor.py	93.51% <0.00%> (-0.13%)	⬇️
... and 16 more

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[iindyk]

retest this please

[iindyk]

retest this please

[iindyk]

the failing tests seem to be unrelated

[lukecwik]

Policy is to merge on green unless its a fix to an issue when there are multiple ongoing issues (e.g. less tests fail then before).

[iindyk]

retest this please

[robertwb]

Jenkins is happy with this change,