Feat: Add APPROX_MOST_FREQUENT Aggregation Function

[FearfulTomcat27]

This pull request introduces a new feature for approximate most frequent value aggregation (approx_most_frequent) in Apache IoTDB. It includes changes to support this functionality in the query engine, test cases, and dependency updates. Below are the key changes:

Feature Implementation: Approximate Most Frequent Aggregation

• New Abstract Class for Accumulators: Added AbstractApproxMostFrequentAccumulator to handle common logic for approximate most frequent value aggregation. It includes methods for intermediate and final evaluations, reset functionality, and unsupported statistics handling. (iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/AbstractApproxMostFrequentAccumulator.java)

• Specific Accumulators: Introduced specialized accumulator classes such as BinaryApproxMostFrequentAccumulator and BlobApproxMostFrequentAccumulator to handle different data types, including binary and blob data. (iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/BinaryApproxMostFrequentAccumulator.java, iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/BlobApproxMostFrequentAccumulator.java) [1] [2]

• Accumulator Factory Enhancements: Updated AccumulatorFactory to support APPROX_MOST_FREQUENT aggregation type, with methods to create grouped and table accumulators for various data types. (iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/AccumulatorFactory.java) [1] [2] [3]

Dependency Updates

• Added Dependency for Stream Library: Included com.clearspring.analytics:stream (version 2.9.8) to support space-saving data structures used in the new aggregation functionality. (iotdb-core/datanode/pom.xml)

Testing

• Integration Tests: Added a new test case approxMostFrequentTest to verify the functionality of the approx_most_frequent aggregation. The test includes queries for different scenarios and validates the results against expected outputs. (integration-test/src/test/java/org/apache/iotdb/relational/it/query/recent/IoTDBTableAggregationIT.java)

Refactoring and Adjustments

• Refactored Approximation Logic: Adjusted imports and dependencies in ApproxCountDistinctAccumulator to align with the new structure for approximate aggregations. (iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/ApproxCountDistinctAccumulator.java) [1] [2]

[JackieTien97]

avoid using this dependency, it seems that it has stopped to be maintained and has a lot of CVEs.