a database cursor is a mechanism that enables traversal over the records in a query result

• 多用于存储过程，性能优化
• akin to the programming language concept of iterator
• 化批为流: cursor用于对结果集（批形态）进行流处理
  • 性能优化：save you memory, less lock for concurrent reads and writes on other rows
  • 性能劣化：重复的网络协商成本，更低的全量压缩比，更低的consistency level

和查询结果集对比

a SQL result is like a bag, you get to hold a whole bunch of rows at once, but not any of them individually. e.g.

• downloading an video in one swoop

a SQL cursor is like a pair of tweezers (picker). With it, you can reach into the bag and grab a row, and then move onto the next.

• video streaming