[#24789] Mention prism is the new default Go SDK runner in CHANGES.md (…

…#27816)

* mention prism in changes.md

* ws lint

* review comments

---------

Co-authored-by: lostluck <[email protected]>

CHANGES.md

@@ -54,40 +54,44 @@
 
 ## Highlights
 
-* New highly anticipated feature X added to Python SDK ([#X](https://github.com/apache/beam/issues/X)).
-* New highly anticipated feature Y added to Java SDK ([#Y](https://github.com/apache/beam/issues/Y)).
 * Spark 3.2.2 is used as default version for Spark runner ([#23804](https://github.com/apache/beam/issues/23804)).
+* The Go SDK has a new default local runner, called Prism ([#24789](https://github.com/apache/beam/issues/24789)).
 
 ## I/Os
 
-* Support for X source added (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
 * Python GCSIO is now implemented with GCP GCS Client instead of apitools ([#25676](https://github.com/apache/beam/issues/25676))
 * Java KafkaIO now supports picking up topics via topicPattern ([#26948](https://github.com/apache/beam/pull/26948))
 * Support for read from Cosmos DB Core SQL API ([#23604](https://github.com/apache/beam/issues/23604))
 * Upgraded to HBase 2.5.5 for HBaseIO. (Java) ([#27711](https://github.com/apache/beam/issues/19554))
 
 ## New Features / Improvements
 
-* X feature added (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
 * The Go SDK now requires Go 1.20 to build. ([#27558](https://github.com/apache/beam/issues/27558))
+* The Go SDK has a new default local runner, Prism. ([#24789](https://github.com/apache/beam/issues/24789)).
+  * Prism is a portable runner that executes each transform independantly, ensuring coders.
+  * At this point it supercedes the Go direct runner in functionality. The Go direct runner is now deprecated.
+  * See https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/runners/prism/README.md for the goals and features of Prism.
 
 ## Breaking Changes
 
-* Legacy runner support removed from Dataflow, all pipelines must use runner v2.
+* Python SDK: Legacy runner support removed from Dataflow, all pipelines must use runner v2.
 
 ## Deprecations
 
-* X behavior is deprecated and will be removed in X versions ([#X](https://github.com/apache/beam/issues/X)).
+* The Go Direct Runner is now Deprecated. It remains available to reduce migration churn.
+  * Tests can be set back to the direct runner by overriding TestMain: `func TestMain(m *testing.M) { ptest.MainWithDefault(m, "direct") }`
+  * It's recommended to fix issues seen in tests using Prism, as they can also happen on any portable runner.
+  * Use the generic register package for your pipeline DoFns to ensure pipelines function on portable runners, like prism.
+  * Do not rely on closures or using package globals for DoFn configuration. They don't function on portable runners.
 
 ## Bugfixes
 
 * Fixed DirectRunner bug in Python SDK where GroupByKey gets empty PCollection and fails when pipeline option `direct_num_workers!=1`.([#27373](https://github.com/apache/beam/pull/27373))
 * Fixed BigQuery I/O bug when estimating size on queries that utilize row-level security ([#27474](https://github.com/apache/beam/pull/27474))
-* Fixed X (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
 
 ## Known Issues
 
-* ([#X](https://github.com/apache/beam/issues/X)).
+* TBD
 
 
 # [2.49.0] - 2023-07-17