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Hide behind `distributed_optimize_skip_select_on_unused_shards` setting.
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This pull request adds
distributed_optimize_skip_select_on_unused_shards. When doing SELECT from Distributed tables, it will try to perform constant folding for sharding expression, based on constraints from WHERE condition, and determine if it's possible to query a subset of nodes of a cluster.It's useful to:
It assumes that data is sharded according to sharding key, it might not be true, that's why it isn't enabled by default.
Limitations:
ANDandOR, doesn't handle queries likeSELECT ... FROM ... WHERE jumpConsistentHash(x, 2) = 1NB: the last time I wrote C++ was 10 years ago
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