Remove Vectorization 2.0 Implementation

[footka]

Description

This is a feature request to remove the Vectorization 2.0 framework from the codebase. The proposal is to retain Vectorization 1.0 (controlled by the _rowsets_enabled parameter) and remove the Vectorization 2.0 components (controlled by use_rich_format_ and _enable_rich_vector_format parameters).

Technical Context

Vectorization 1.0:

1. Operators process multiple rows per call: get_next_row -> get_next_batch.
2. Expressions compute a batch at a time: expr->eval -> expr->eval_batch.
3. Storage decodes data in batches to ObDatum.

Vectorization 2.0:

Vectorization 2.0 is an extension of 1.0, focusing on changes to the "physical representation of each column" and the "computational kernel".

Changes in Physical Representation:

• 1.0: Each column is a fixed array of ObDatum datums[256].
• 2.0: Dynamically selects different formats (IVector/Rich Format) based on data type and source to reduce format conversion, branching, and data access overhead, and provides opportunities for SIMD optimization for some operators.
  • VEC_FIXED: Fixed-length basic types (e.g., int, float).
  • VEC_CONTINUOUS: Multiple variable-length varchars stored on a contiguous memory block.
  • VEC_DISCRETE: For example, string content of varchar expressions after operator computation stored in discrete memory.
  • VEC_UNIFORM: Compatible with the ObDatum representation from 1.0.
  • VEC_UNIFORM_CONST

Changes in Computational Kernel:

eval_batch_func_ -> eval_vector_func_: The latter supports multiple columnar memory formats and type specialization.

Code Impact

The removal will affect the following code paths:

src/sql/engine/vector/**
src/sql/engine/expr/vector_cast/**

# Various vec operators
src/sql/engine/aggregate/ob_exec_hash_struct_vec.*
src/sql/engine/basic/ob_limit_vec_op.*
src/sql/engine/join/ob_join_vec_op.*

# Rich Aggregate new framework
src/sql/engine/aggregate/
Should retain ObAggregateProcessor, remove share::aggregate::Processor

src/sql/dtl/ob_dtl_vectors_buffer.cpp
src/sql/dtl/ob_dtl_vectors_buffer.h


# storage
src/storage/blocksstable/encoding/*
src/storage/access/ob_aggregated_store_vec.*
src/storage/access/ob_pushdown_aggregate_vec.*

Additional Notes

• Regarding session pool overhead: The actual overhead is in Session allocation, which is now dynamic. This pool has minimal practical effect.
• For issues reported by external business teams, please correctly select the "Work Item Type" on the right based on the actual situation:
  • Customer Service Feedback: Specifically refers to issues before deployment/POC, clearly identified as product bugs requiring fixes and release.
  • Online Issue: Issues that have occurred after deployment, clearly identified as product bugs, but not classified as a fault.
  • Online Fault: Issues that have occurred after deployment, clearly identified as product bugs, causing business errors or negative impact on the customer side (the interpretation of a fault belongs to the delivery service team).