gemini:

This appears to be a substantial feature addition and refactoring aimed at supporting Session Windows based on custom start/end events (via EMIT AFTER SESSION CLOSE) and introducing TTL (Time-To-Live) support for Hybrid Hash Tables (spill-to-disk storage) using RocksDB compaction filters.

Here is a summary and review of the changes:

1. RocksDB Integration Refactoring

The existing RocksHandler and Rocks classes are being replaced/renamed to RocksDBColumnFamilyHandler and RocksDB.

• Purpose: To support per-Column-Family TTLs dynamically.
• Mechanism:
  • RocksDB class now manages rocksdb::DB and handles the lifecycle of column families.
  • It persists TTL metadata (__tp_meta_ttl__.<cf_name>) into the default column family so that when the DB is reopened, the correct TTLs are applied to specific column families.
  • A custom RocksDBTTLCompactionFilter is implemented to filter out expired keys during RocksDB compaction based on a timestamp suffix appended to the value.
• Impact: This allows HybridHashTable (used in Joins and Aggregations) to automatically clean up old state on disk without explicit cleanup scans, which is crucial for long-running streaming queries.

2. Hybrid Hash Table Updates

• Configuration: HybridHashTableConfig now includes ttl and kv_options.
• Logic:
  • The value serialization logic in HybridHashTable (and HybridKeyList) now optionally appends a timestamp if TTL is enabled.
  • HybridKeyList (used for tracking timeouts) was refactored to support removing specific keys (removeKey) and handling timeouts more efficiently (removeTimedOutKeys), including refilling from disk when the in-memory buffer is exhausted.

3. EMIT AFTER SESSION CLOSE

This is the core functional addition.

• Syntax: EMIT AFTER SESSION CLOSE IDENTIFIED BY (ts_col, start_cond, end_cond) WITH MAXSPAN ....
• Logic (HybridAggregator):
  • A new execution path executeAndFinalizeAfterSessionClose is added.
  • It maintains a state machine per key:
    • New Session: If a key is not found and start_cond is true (or implied), a new session is created.
    • Merge: If merge_open_sessions is enabled, new start events merge into existing sessions. Otherwise, the old session is closed (emitted) and a new one starts.
    • End Session: If end_cond is true, the session is finalized and emitted. The include_session_end setting controls if the ending row is included in the aggregate.
    • Timeout/MaxSpan: The HybridKeyList tracks the creation timestamp of sessions. If a session exceeds MAXSPAN (checked per row) or TIMEOUT (checked via removeTimedOutKeys), it is forcibly closed/emitted.

4. Integration

• The AggregatingStep and AggregatingTransform are updated to initialize the RocksDB/Hybrid configuration with the new TTL settings passed from query settings (aggregate_state_ttl_sec).
• ParserEmitQuery is updated to parse the new syntax, supporting various overloads of IDENTIFIED BY (e.g., tuple for start/end columns).

Code Quality & Correctness Checks

• TTL Implementation: Storing TTL metadata in the default CF is a robust way to ensure persistence across restarts. The compaction filter logic looks standard for RocksDB.
• Session Logic: The implementation in HybridAggregator_ExecuteAndFinalize.cpp covers edge cases like "End event without start" (orphan events) and "Start event while open".
• Memory Management: The usage of std::shared_ptr for RocksDB instances and handlers seems correct to manage lifecycles.
• Tests: The SQL test 99109_emit_after_session_close.sql covers many permutations (only maxspan, start/end columns, merging). Unit tests for the new RocksDB wrapper are included.