The original motivation for this commit was that shared_ptr_helper used
std::shared_ptr<>() which does two heap allocations instead of
make_shared<>() which does a single allocation. Turned out that
1. the affected code (--> Storages/) is not on a hot path (rendering the
performance argument moot ...)
2. yet copying Storage objects is potentially dangerous and was
previously allowed.
Hence, this change
- removes shared_ptr_helper and as a result all inherited create() methods,
- instead, Storage objects are now created using make_shared<>() by the
caller (for that to work, many constructors had to be made public), and
- all Storage classes were marked as noncopyable using boost::noncopyable.
In sum, we are (likely) not making things faster but the code becomes
cleaner and harder to misuse.
The check is currently *not* part of .clang-tidy. It complains about:
(1) "switch has multiple consecutive identical branches"
(2) "repeated branch in conditional chain"
About (1): Lots of findings in switches were about redundant
"[[fallthrough]]" in places where the compiler would not warn anyways. I
have cleaned these up.
About (2): In if-else_if-else chains, fixing the warning would usually
mean concatenating multiple if-conditions. As this would reduce
readability in most cases, I did not fix these places.
Because of (2), I also refrained from adding "bugprone-branch-clone" to
.clang-tidy.
ALTER DROP COLUMN of nested column did not requires mutation before, and
so it leaves nested column as-is, and in case of compact parts
subsequent alter, that requires mutation, will trigger READ_COLUMN of
that nested column (because it exists in part), but it will fail because
there is no such column in the table already.
Here is example of such a failure on CI - [1].
[1]: https://s3.amazonaws.com/clickhouse-test-reports/35459/52099b23a1cb9a7ff036c5c60aa037c999b333ef/stateless_tests__thread__actions__[1/3].html
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
