In v0.2, we focus on sorting everything -- from the composite sort key and primary key indexing in storage layer, to sort merge executors in executor layer, to composite key support in catalog.

Storage

• storage: support composite sort key in MergeIterator #588
• storage: support range-filter scan by sort key #589
• refactor storage to support snapshot isolation
• refactor VersionManager to include catalog

Optimizer

• filter push-down optimizer rule for all operators
• support column pruning for some operators #654
• add property to plan nodes optimizer: add property sorted to plan nodes #601

Executor

• optimize NestedLoopJoin to pull fewer data in memory executor: optimize NestedLoopJoin's memory usage #592
• executor: implement SortAgg #591
• executor: implement SortMergeJoin #597
• new expression framework to vectorize any scalar function and support type inference

SQL

• support subquery in binder binder: bind subqueries #578
• add function call support feat(function): add function definition #581
• make catalog consistent catalog: use a single lock for catalog #590

Tutorial

• basic query engine (expected April)
• query execution
• storage

Test Framework

• test: introduce planner and optimizer test #593

We're still drafting detailed design for each item, stay tuned! If you are interested in any of the item, please ping us in community channel for instructions, or create a tracking issue for that, thanks!