feat: PolarDB graph backend with decomposed mixin architecture

[anatolykoptev]

Summary

Overhaul of the graph_dbs/ module:

• PolarDB backend: decomposed from a 4200-line monolith into a mixin-based polardb/ package (11 files, ~4300 lines). Each mixin handles a logical concern (connection, nodes, edges, search, filters, etc.)
• Shared utilities (utils.py): extracted common helpers used across backends
• BaseGraphDB extended with 8 new abstract methods for full-text search, tag-based neighbors, edge queries, and user management
• Neo4j/Nebula backends updated to implement new abstract methods
• Bug fix: self.execute_query() in count_nodes() didn't exist — replaced with standard cursor pattern

PolarDB package structure

File	Lines	Responsibility
__init__.py	30	Composes all mixins into PolarDBGraphDB
connection.py	334	Pool management, health checks, retries
schema.py	172	AGE extensions, tables, indexes
nodes.py	715	Node CRUD + agtype parsing
edges.py	267	Edge CRUD
filters.py	582	Dual SQL/Cypher WHERE clause builders
search.py	361	Keyword, fulltext, embedding search
traversal.py	432	Neighbors, subgraph, paths
queries.py	658	Metadata queries, counts
maintenance.py	769	Import/export, clear, cleanup
helpers.py	14	Standalone utility functions

Import path unchanged

from memos.graph_dbs.polardb import PolarDBGraphDB  # works as before

Test plan

• All 31 BaseGraphDB abstract methods implemented in PolarDB (verified via AST)
• No cross-mixin import violations (mixins use self. for cross-calls)
• Existing test suite passes across all backends
• PolarDB search operations work end-to-end

🤖 Generated with Claude Code

[wustzdy]

Thank you for your optimization and updates to the underlying PolarDB code in the memos open-source project. Currently, PolarDB utilizes two plugins: polardb_age and vector. While vector is open-source, polardb_age is built upon Apache AGE with significant enhancements and upgrades. For instance, it supports graph_id, which serves as a bridge for connecting edges between different nodes.

As you can see from the polardb_age GitHub repository page, this plugin indeed incorporates numerous optimizations and functional extensions based on Apache AGE. It introduces new functions such as graph_i, graph_s, and graph_p, along with more efficient parallel processing and multi-graph support, among other features.

You can proceed with optimization and upgrades in postgres.py. The combination of pg_vector, Apache AGE, and multi-table joins is capable of supporting some fundamental functionalities to meet requirements.