Andrew Wong created KUDU-3137:
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Summary: Allow RYW scan mode to return rows if the picked
timestamp is lower than the ancient history mark
Key: KUDU-3137
URL: https://issues.apache.org/jira/browse/KUDU-3137
Project: Kudu
Issue Type: Improvement
Components: client, tserver
Reporter: Andrew Wong
Thomas mentioned in the comment in IMPALA-7184,
{code:java}
- I create a Kudu table, insert some stuff into it, scan it back at
READ_YOUR_WRITES. Everything works as expected.
- I wait greater than 'tablet_history_max_age_sec' and attempt to scan it
again at READ_YOUR_WRITES (using either the same KuduClient or a new one). This
results in an error of the form 'Snapshot timestamp is earlier than the ancient
history mark...'
{code}
Today, the snapshot used to scan in RYW mode is {{max(propagated timestamp + 1,
clean time)}}. If the tablet hasn't been written to recently, a tablet's clean
time can fall well before the AHM. If there are no ops in flight, it might be
worth considering some other timestamps, e.g. now, now minus the AHM, the
current safe time, etc., or escalating a {{RYW}} scan to {{READ_LATEST}} if the
propagated timestamp has passed.
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