cstore_fdwPostgreSQL 柱状存储扩展

cstore_fdw 实现了 PostgreSQL 数据库的柱状存储，用于对批量加载的数据进行分析的场景。

该扩展使用了 Optimized Row Columnar (ORC) 格式的数据存储布局。ORC 提升 Facebook 开发的 RCFile 格式，带来如下好处：

• 压缩: Reduces in-memory and on-disk data size by 2-4x. Can be extended to support different codecs.

• 列预测: Only reads column data relevant to the query. Improves performance for I/O bound queries.

• 跳过索引: Stores min/max statistics for row groups, and uses them to skip over unrelated rows.

此外，我们使用了 PostgreS 外部数据封装 API 和类型呈现，带来：

• Support for 40+ Postgres data types. The user can also create new types and use them.

• Statistics collection. PostgreSQL's query optimizer uses these stats to evaluate different query plans and pick the best one.

• Simple setup. Create foreign table and copy data. Run SQL.