[PR] Adds drain support to Spanner CDC source. [beam]

Thu, 03 Sep 2026 11:37:42 -0700 


acrites opened a new pull request, #39994:
URL: https://github.com/apache/beam/pull/39994

   Before this change, we were calling the default implementation of 
truncateRestriction on drain, which, for bounded restrictions tries to finish 
evaluating the entire restriction. Both SDF's in the Spanner CDC source use 
bounded restrictions that are effectively unbounded. Overriding 
truncateRestriction to return null on these SDFs allows terminating immediately.
   
   In addition, we had to change the cleanup action from DROP TABLE to DROP 
TABLE IF EXISTS to make deletion idempotent. Otherwise, if that work item gets 
retried by the backend, it will start fail-looping, preventing drain from 
completing.
   
   We don't have a great way to test drain here, but I ran a test pipeline on 
Dataflow and verified that it can now drain successfully.
   
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