[GitHub] [flink] aljoscha commented on a change in pull request #14312: [FLINK-20491] Support Broadcast State in BATCH execution mode

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aljoscha commented on a change in pull request #14312:
URL: https://github.com/apache/flink/pull/14312#discussion_r551345782



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File path: docs/dev/datastream_execution_mode.md
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@@ -237,6 +237,35 @@ next key.
 See [FLIP-140](https://cwiki.apache.org/confluence/x/kDh4CQ) for background
 information on this.
 
+### Order of Processing
+
+The order in which records are processed in operators or user-defined functions (UDFs) can differ between `BATCH` and `STREAMING` execution.
+
+In `STREAMING` mode, user-defined functions should not make any assumptions about incoming records' order.
+Data is processed as soon as it arrives.
+
+In `BATCH` execution mode, there are some operations where Flink guarantees order. 
+The ordering can be a side effect of the particular task scheduling,
+network shuffle, and state backend (see above), or a conscious choice by the system.
+
+There are three general types of input that we can differentiate:
+
+- _broadcast input_: input from a broadcast stream (see also [Broadcast
+  State]({% link dev/stream/state/broadcast_state.md %}))
+- _regular input_: input that isn't any of the above types of input

Review comment:
       regular input should be processed before keyed input, because the (sorted) keyed input is always last.




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