IssueTracker

The customer is experiencing issues related to transaction drops when inserting into Spanner, which is impacting their throughput at higher volumes.

They are encountering ALREADY_EXISTS errors intermittently, which suggest that the transactions may already be present or being retried due to race conditions, causing failures during insertion.
They have scaled up the Processing Units (PUs) from 8000 to 20000, which might suggest you're trying to handle a higher transaction load. This scaling effort, however, doesn't seem to fully resolve the issue of transaction drops, pointing to possible bottlenecks elsewhere in the pipeline or transaction handling