Details
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Improvement
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Status: Open
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Normal
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Resolution: Unresolved
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None
Description
Today's DTCS implementation has been discussed and debated in a few JIRAs already (the notable one is https://issues.apache.org/jira/browse/CASSANDRA-9666). One of the main challenges with the current approach is that it is very difficult to reason about how the "Target" class makes buckets, thus making it difficult to reason about the expected file layout on disk.
I am proposing a simplification to current approach that keeps most of the DTCS properties intact that makes it a great fit for time-series data. The simplification is as follows.
Given the min and max timestamps across all SS Tables in question, start from min and make windows based on base and min_threshold. The logic in GetWindow simply tries to fit maximum sized windows from min to max.
This keeps the DTCS properties intact except that we don't need to wait for min_threshold windows before making a bigger one. I would argue this simplifies the algorithm to a great extent, is easy to reason about and the end result isn't drastically different than the original DTCS in most cases. We give up on the "alignment" logic that exists in current implementation, but I honestly don't think it buys us a lot besides complexity.
The implementation can obviously be optimized and cleaned up more if folks think this is a good idea.