The following headers are pretty generic, so use forward declaration as
much as possible:
- Context.h
- Settings.h
- ConnectionTimeouts.h
(Also this shows that some missing some includes -- this has been fixed)
And split ConnectionTimeouts.h into ConnectionTimeoutsContext.h (since
module part cannot be added for it, due to recursive build dependencies
that will be introduced)
Also remove Settings from the RemoteBlockInputStream/RemoteQueryExecutor
and just pass the context, since settings was passed only in speicifc
places, that can allow making a copy of Context (i.e. Copier).
Approx results (How much units will be recompiled after changing file X?):
- ConnectionTimeouts.h
- mainline: 100
- Context.h:
- mainline: ~800
- patched: 415
- Settings.h:
- mainline: 900-1K
- patched: 440 (most of them because of the Context.h)
Consider the following example:
CREATE TABLE test(p DateTime, k int) ENGINE MergeTree PARTITION BY toDate(p) ORDER BY k;
INSERT INTO test VALUES ('2020-09-01 00:01:02', 1), ('2020-09-01 20:01:03', 2), ('2020-09-02 00:01:03', 3);
- SELECT count() FROM test WHERE toDate(p) >= '2020-09-01' AND p <= '2020-09-01 00:00:00'
In this case rpn will be (FUNCTION_IN_RANGE, FUNCTION_UNKNOWN (due to strict), FUNCTION_AND)
and for optimize_trivial_count_query we cannot use index if there is at least one FUNCTION_UNKNOWN.
since there is no post processing and return count() based on only the first predicate is wrong.
Before this patch FUNCTION_UNKNOWN was allowed for optimize_trivial_count_query, and the result was wrong.
And two examples above just to show the difference, the behaviour hadn't been changed with this patch:
- SELECT * FROM test WHERE toDate(p) >= '2020-09-01' AND p <= '2020-09-01 00:00:00'
In this case will be (FUNCTION_IN_RANGE, FUNCTION_IN_RANGE (due to non-strict), FUNCTION_AND)
so it will prune everything out and nothing will be read.
- SELECT * FROM test WHERE toDate(p) >= '2020-09-01' AND toUnixTimestamp(p)%5==0
In this case will be (FUNCTION_IN_RANGE, FUNCTION_UNKNOWN, FUNCTION_AND)
and all, two, partitions will be scanned, but due to filtering later none of rows will be matched.
