Does PGVector really need SQLAlchemy URLs? If so, why not psycopg3?

[khteh]

When I use postgresql scheme, I hit this error:

  File "/usr/src/Python/rag-agent/src/Infrastructure/VectorStore.py", line 87, in __init__
    self.vector_store = PGVector(
                        ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        embeddings = self._embeddings,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
        async_mode = True
        ^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/khteh/.local/share/virtualenvs/rag-agent-YeW3dxEa/lib/python3.13/site-packages/langchain_postgres/vectorstores.py", line 434, in __init__
    self._async_engine = create_async_engine(
                         ~~~~~~~~~~~~~~~~~~~^
        connection, **(engine_args or {})
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/khteh/.local/share/virtualenvs/rag-agent-YeW3dxEa/lib/python3.13/site-packages/sqlalchemy/ext/asyncio/engine.py", line 120, in create_async_engine
    sync_engine = _create_engine(url, **kw)
  File "<string>", line 2, in create_engine
  File "/home/khteh/.local/share/virtualenvs/rag-agent-YeW3dxEa/lib/python3.13/site-packages/sqlalchemy/util/deprecations.py", line 281, in warned
    return fn(*args, **kwargs)  # type: ignore[no-any-return]
  File "/home/khteh/.local/share/virtualenvs/rag-agent-YeW3dxEa/lib/python3.13/site-packages/sqlalchemy/engine/create.py", line 602, in create_engine
    dbapi = dbapi_meth(**dbapi_args)
  File "/home/khteh/.local/share/virtualenvs/rag-agent-YeW3dxEa/lib/python3.13/site-packages/sqlalchemy/dialects/postgresql/psycopg2.py", line 696, in import_dbapi
    import psycopg2
ModuleNotFoundError: No module named 'psycopg2'

(1) Why psycopg2 instead of psycopg3 (https://www.psycopg.org/psycopg3/docs/basic/install.html)?

(2) Does it actually need SQLAlchemy URLs since it is PGVector? Why not directly using the postgresql scheme?