Add watermark generator

[dai-chen]

Signed-off-by: Chen Dai [email protected]

Description

Watermark is a monotonically increasing timestamp of the oldest work not yet completed. The work can be any grouping operation, such as aggregate or join, that accumulate stream events to a table and maintain the state. In other words, watermark is the way of how we reason about the completeness of accumulated window state.

There are several aspects of watermark implementation, including watermark generation, watermark emit frequency and watermark propagation. This PR is focused on the watermark generation which has no dependency on how we integrate with query plan later.

What's covered in this PR is the common generate strategy: Bounded Out-Of-Order Watermark Generator which allows a fixed delay for disordered data.

Issues Resolved

#953

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

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[codecov-commenter]

Codecov Report

Merging #959 (98f55f6) into feature/maximus-m1 (91baab1) will decrease coverage by 35.19%.
The diff coverage is n/a.

@@                    Coverage Diff                    @@
##             feature/maximus-m1     #959       +/-   ##
=========================================================
- Coverage                 97.96%   62.76%   -35.20%     
=========================================================
  Files                       303       10      -293     
  Lines                      7805      658     -7147     
  Branches                    504      119      -385     
=========================================================
- Hits                       7646      413     -7233     
- Misses                      158      192       +34     
- Partials                      1       53       +52     

Flag	Coverage Δ
query-workbench	62.76% <ø> (?)
sql-engine	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...g/opensearch/sql/expression/LiteralExpression.java
...opensearch/sql/expression/HighlightExpression.java
...ensearch/sql/planner/logical/LogicalHighlight.java
...on/window/aggregation/AggregateWindowFunction.java
.../opensearch/sql/opensearch/executor/Scheduler.java
.../org/opensearch/sql/data/model/ExprValueUtils.java
...l/expression/window/frame/PeerRowsWindowFrame.java
...arch/planner/logical/rule/MergeAggAndRelation.java
...ch/sql/prometheus/client/PrometheusClientImpl.java
...nsearch/sql/analysis/SelectExpressionAnalyzer.java
... and 303 more

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[penghuo]

LGTM