[GitHub] [beam] lukecwik commented on a change in pull request #15235: [BEAM-7745] Avoid uncached state fetches for streaming side-inputs

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lukecwik commented on a change in pull request #15235:
URL: https://github.com/apache/beam/pull/15235#discussion_r681952111



##########
File path: runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillStateInternals.java
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@@ -474,9 +474,12 @@ private WindmillValue(
 
     @Override
     public void clear() {
-      modified = true;
+      // if the value was already null (because it was already cleared) then there's no need to

Review comment:
       Did you mean to include this as part of your change?

##########
File path: runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillStateInternals.java
##########
@@ -474,9 +474,12 @@ private WindmillValue(
 
     @Override
     public void clear() {
-      modified = true;
+      // if the value was already null (because it was already cleared) then there's no need to
+      // mark this as modified again.  This will save having to persist a clear that does nothing.

Review comment:
       Wouldn't two calls to `clear()` toggle `modified` from `true` to `false`?
   
   I think you would need to keep track of whether the value state is already in a cleared state instead of using ` value == null` as a proxy.
   
   This logic could really use unit tests to validate such simple scenarios.
   




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