Perf regression in SQL Query3 in Dataflow

Nexmark shows perf regression in SQL Query3 starting on July 30 2019: https://apache-beam-testing.appspot.com/explore?dashboard=5670405876482048

There doesn't seem to be a lot of changes to SQL around that date and the one that was there doesn't seem relevan to the query: https://github.com/apache/beam/commits/master/sdks/java/extensions/sql

Direct runner shows a slight perf decrease as well: https://apache-beam-testing.appspot.com/explore?dashboard=5084698770407424 while Spark runner doesn't: https://apache-beam-testing.appspot.com/explore?dashboard=5138380291571712

The query in question is a join with a simple filter condition: https://github.com/apache/beam/blob/b8aa8486f336df6fc9cf581f29040194edad3b87/sdks/java/testing/nexmark/src/main/java/org/apache/beam/sdk/nexmark/queries/sql/SqlQuery3.java#L69

Other queries don't seem to be affected