feat: add support for PolarDB

[nanlongyu]

Description

This PR introduces support for PolarDB, an Alibaba Cloud cloud-native relational database service, as a new database engine in VectorDBBench. PolarDB features IMCI (In-Memory Column Index) based vector search capabilities, leveraging FAISS as its underlying vector engine. It is compatible with the MySQL protocol, offering high-performance and cost-effective vector retrieval on top of a fully-managed cloud-native architecture with features like storage-compute separation, read-write splitting, and elastic scaling — making it well-suited for enterprise-level AI and similarity search scenarios.

Supported Index Types：

• HNSW：High-performance graph-based indexing with full-precision vectors, providing the best recall quality.
• HNSWPQ：Combines HNSW graph navigation with Product Quantization for memory-efficient retrieval at scale.
• HNSWSQ：Combines HNSW graph navigation with Scalar Quantization, balancing speed, memory usage, and recall.

[nanlongyu]

/assign @XuanYang-cn

[XuanYang-cn]

Thanks for the contribution! The overall structure follows the VectorDBBench client pattern well. A few items to address:

CI blocker — lint errors (12 total)

• cli.py:123: line too long (132 > 120 chars)
• cli.py, polardb.py: 8 missing type annotations (_build_db_config(parameters), _create_db_table(cursor, ...), vector_to_hex(v), _insert_batch(...))
• polardb.py: 4 SQL injection warnings — add # noqa: S608 (standard pattern used by AliSQL, MariaDB, TiDB, OceanBase)

DROP DATABASE is too destructive (polardb.py:599)

cursor.execute(f"DROP DATABASE IF EXISTS {self.db_config['database']}")

Other MySQL-based clients (AliSQL, MariaDB) only drop the table, not the entire database. This could wipe out unrelated data. Please change to DROP TABLE IF EXISTS.

raise e from None hides traceback (polardb.py:656)

raise e from None suppresses the original exception chain. Use raise instead to preserve the full traceback for debugging.

Redundant COMMIT with autocommit=True

The connection is created with autocommit=True, but there are several explicit cursor.execute("COMMIT") calls throughout. Pick one approach — either use autocommit or manage transactions manually.

Config field duplication (config.py)

PolarDBHNSWFlatConfig, PolarDBHNSWPQConfig, and PolarDBHNSWSQConfig duplicate M, ef_construction, ef_search, insert_workers, post_load_index. Consider extracting a shared PolarDBHNSWBaseConfig (similar to how PolarDBHNSWTypedDict already works for the CLI side).

[nanlongyu]

hi @XuanYang-cn , thanks for your comments. All issues have been fixed and it seems that all checks have passed. Please review again.

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