[flink] 02/04: [refactor][streaming] Improved description of the calculation of the processing time delay

[pn...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

pnowojski pushed a commit to branch release-1.14
in repository https://gitbox.apache.org/repos/asf/flink.git

commit 6fa603327c7a2aeda0c2416c36e763949832da02
Author: Anton Kalashnikov <ka...@yandex.ru>
AuthorDate: Wed Sep 1 15:30:57 2021 +0200

    [refactor][streaming] Improved description of the calculation of the processing time delay
---
 .../streaming/runtime/tasks/ProcessingTimeServiceUtil.java     | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeServiceUtil.java b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeServiceUtil.java
index c718f49..3733d8a 100644
--- a/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeServiceUtil.java
+++ b/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/ProcessingTimeServiceUtil.java
@@ -26,6 +26,8 @@ public class ProcessingTimeServiceUtil {
 
     /**
      * Returns the remaining delay of the processing time specified by {@code processingTimestamp}.
+     * This delay guarantees that the timer will be fired at least 1ms after the time it's
+     * registered for.
      *
      * @param processingTimestamp the processing time in milliseconds
      * @param currentTimestamp the current processing timestamp; it usually uses {@link
@@ -36,9 +38,11 @@ public class ProcessingTimeServiceUtil {
 
         // Two cases of timers here:
         // (1) future/now timers(processingTimestamp >= currentTimestamp): delay the firing of the
-        //   timer by 1 ms to align the semantics with watermark. A watermark T says we won't see
-        //   elements in the future with a timestamp smaller or equal to T. With processing time, we
-        //   therefore need to delay firing the timer by one ms.
+        //   timer by 1 ms to align the semantics with watermark. A watermark T says we
+        //   won't see elements in the future with a timestamp smaller or equal to T. Without this
+        //   1ms delay, if we had fired the timer for T at the timestamp T, it would be possible
+        //   that we would process another record for timestamp == T in the same millisecond, but
+        //   after the timer for the timsetamp T has already been fired.
         // (2) past timers(processingTimestamp < currentTimestamp): do not need to delay the firing
         //   because currentTimestamp is larger than processingTimestamp pluses the 1ms offset.
         // TODO. The processing timers' performance can be further improved.