Parquet files unreadable after upgrade
A nightly job writes Parquet files to your data lake; downstream Spark/Trino jobs read them for reporting. After a library bump in the writer image at 01:00, last night's partitions *write* fine and a few readers succeed, but most reader jobs fail with 'unsupported/unknown compression codec' or read garbage column values, while older partitions read perfectly. Dashboards: writer job exit code 0, file counts and sizes look normal in object storage. How do you triage, stop producing unreadable partitions, and recover the data?
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 35 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.