Barriers（数据屏障）

Posted 2020-12-11 zgq25302111

A core element in Flink’s distributed snapshotting are the stream barriers. These barriers are injected into the data stream and flow with the records as part of the data stream. Barriers never overtake records, they flow strictly in line. A barrier separates the records in the data stream into the set of records that goes into the current snapshot, and the records that go into the next snapshot. Each barrier carries the ID of the snapshot whose records it pushed in front of it. Barriers do not interrupt the flow of the stream and are hence very lightweight. Multiple barriers from different snapshots can be in the stream at the same time, which means that various snapshots may happen concurrently.

 

Flink 分布式快照的核心元素是 Barriers（数据屏障）。数据屏障被注入数据流，随数据流流动，成为数据流的一部分。数据屏障永远不会超车，它们严格按照顺序流动。一个数据屏障将数据流中的记录分隔为进入当前快照的记录集和进入下一个快照的记录集。每个数据屏障都携带快照ID，数据屏障推动该快照记录向前流动。数据屏障不会干扰数据流，因此是非常轻量级的。数据流中可能同时存在来自不同快照的多个数据屏障，这意味着各种快照可能并发发生。