keith-turner commented on PR #2665:
URL: https://github.com/apache/accumulo/pull/2665#issuecomment-1153019085
> It's not the scan execution hints that are modifying the behavior... it's
the configured dispatcher. And, the scan hints are still not affecting the data
returned... it's the server that it was dispatched to that is doing that.
If scan hints+config can change the behavior of a scanner from immediate to
eventual I think this could lead to disaster. Consider something like the
Accumulo GC algorithm where its correctness relies on only using scanners with
immediate consistency. Consider the following situation.
* Person A writes a scanner that requires immediate consistency and sets a
scan hint with intention of changing cache behavior to be opportunistic.
* Later Person B changes Accumulo configuration such that it causes the
scan hints set by person A to now make the scanner coded by person A be
eventually consistent.
If the code in question were the Accumulo GC, this could cause files to be
deleted when they should not be. Eventual vs immediate consistency is so
important to some algorithms that it should always be explicitly declared per
scanner and never be overridden by config that could impact all scanners in an
indiscriminate manner without consideration of individual circumstances and per
scanner intent.
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