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Phase 2: Execution & Networking

Overview

Phase 2 focused on transforming raw data into results through a standardized execution model and enabling communication between nodes.

Key Components

1. Volcano Execution Engine (`executor/operator.cpp`)

Implemented the standard pull-based iterator model.

Base Operator Class: Defines the init, open, next, and close interface.
Physical Operators:
- SeqScanOperator: Linear scan of heap tables.
- FilterOperator: Expression evaluation using the Value system.
- ProjectOperator: Column transformation and aliasing.
- HashJoinOperator: Efficient in-memory inner joins.

2. Internal RPC Layer (`network/rpc_server.cpp`, `rpc_client.cpp`)

Built a high-performance communication backbone for the cluster.

Binary Protocol: Custom header-payload format for minimal overhead.
Command Routing: Registry-based handler system for different RPC types (ExecuteFragment, TxnPrepare, etc.).
Async Execution: Support for parallel query dispatch to multiple nodes.

3. PostgreSQL Wire Protocol (`network/server.cpp`)

Ensured compatibility with standard SQL tools.

Handshake: Support for startup messages and authentication.
Simple Query Protocol: Enables tools like psql to send SQL strings and receive formatted results.

4. Transaction Management (`transaction/lock_manager.cpp`)

Implemented local concurrency control.

Two-Phase Locking (2PL): Support for Shared (S) and Exclusive (X) locks.
Two-Phase Commit (2PC): Infrastructure for distributed transaction coordination (Prepare/Commit/Abort).

Lessons Learned

The pull-based model simplifies operator composition but requires careful memory management of intermediate results.
Sockets with MSG_WAITALL require strict protocol adherence to avoid deadlocks.