qemu does not support MADV_DONTNEED, and by not support it simply ignore
it (i.e. return 0 -- no error).
This issue has been "fixed" in #15590, however it just
terminates the process, and completely breaks clickhouse under qemu
(see also #15174).
But there is no need in such strong protection, we can stop using
madvise in jemalloc if MADV_DONTNEED does not work properly.
And this is what #18169 was tried to do (by override madvise), however
this will break sanitizers, at least TSAN and UBSAN.
The problem there is that sanitizers initialization code uses madvise
(and there is no way to turn this off with TSAN_OPTIONS) and overwritten
madvise function will have sanitizers traits (__tsan_func_entry), while
TSAN is not ready for this, and eventually it SIGSEGV.
Interesting thing is that in the recent clang-12, madvise was replaced
with direct syscall [1].
[1]: 9f8c4039f2
But it is better to make clickhouse compatible with clang < 12 too, so
instead of override madvise completely, the runtime check was moved into
the jemalloc code [2].
[2]: https://github.com/ClickHouse-Extras/jemalloc/pull/1
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)
v2: Add a note that top_level_domains_lists aren not applied w/o restart
v3: Remove ExtractFirstSignificantSubdomain{Default,Custom}Lookup.h headers
v4: TLDListsHolder: remove FIXME for dense_hash_map (this is not significant)
