- TSA is a static analyzer build by Google which finds race conditions
and deadlocks at compile time.
- It works by associating a shared member variable with a
synchronization primitive that protects it. The compiler can then
check at each access if proper locking happened before. A good
introduction are [0] and [1].
- TSA requires some help by the programmer via annotations. Luckily,
LLVM's libcxx already has annotations for std::mutex, std::lock_guard,
std::shared_mutex and std::scoped_lock. This commit enables them
(--> contrib/libcxx-cmake/CMakeLists.txt).
- Further, this commit adds convenience macros for the low-level
annotations for use in ClickHouse (--> base/defines.h). For
demonstration, they are leveraged in a few places.
- As we compile with "-Wall -Wextra -Weverything", the required compiler
flag "-Wthread-safety-analysis" was already enabled. Negative checks
are an experimental feature of TSA and disabled
(--> cmake/warnings.cmake). Compile times did not increase noticeably.
- TSA is used in a few places with simple locking. I tried TSA also
where locking is more complex. The problem was usually that it is
unclear which data is protected by which lock :-(. But there was
definitely some weird code where locking looked broken. So there is
some potential to find bugs.
*** Limitations of TSA besides the ones listed in [1]:
- The programmer needs to know which lock protects which piece of shared
data. This is not always easy for large classes.
- Two synchronization primitives used in ClickHouse are not annotated in
libcxx:
(1) std::unique_lock: A releaseable lock handle often together with
std::condition_variable, e.g. in solve producer-consumer problems.
(2) std::recursive_mutex: A re-entrant mutex variant. Its usage can be
considered a design flaw + typically it is slower than a standard
mutex. In this commit, one std::recursive_mutex was converted to
std::mutex and annotated with TSA.
- For free-standing functions (e.g. helper functions) which are passed
shared data members, it can be tricky to specify the associated lock.
This is because the annotations use the normal C++ rules for symbol
resolution.
[0] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html
[1] https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/42958.pdf
For async s3 writes final part flushing was defered until all the INSERT
block was processed, however in case of too many partitions/columns you
may exceed max_memory_usage limit (since each stream has overhead).
Introduce max_insert_delayed_streams_for_parallel_writes (with default
to 1000 for S3, 0 otherwise), to avoid this.
This should "Memory limit exceeded" errors in performance tests.
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
In #33291 final part commit had been defered, and now it can take
significantly more time, that may lead to "Part directory doesn't exist"
error during INSERT:
2022.02.21 18:18:06.979881 [ 11329 ] {insert} <Debug> executeQuery: (from 127.1:24572, user: default) INSERT INTO db.table (...) VALUES
2022.02.21 20:58:03.933593 [ 11329 ] {insert} <Trace> db.table: Renaming temporary part tmp_insert_20220214_18044_18044_0 to 20220214_270654_270654_0.
2022.02.21 21:16:50.961917 [ 11329 ] {insert} <Trace> db.table: Renaming temporary part tmp_insert_20220214_18197_18197_0 to 20220214_270689_270689_0.
...
2022.02.22 21:16:57.632221 [ 64878 ] {} <Warning> db.table: Removing temporary directory /clickhouse/data/db/table/tmp_insert_20220214_18232_18232_0/
...
2022.02.23 12:23:56.277480 [ 11329 ] {insert} <Trace> db.table: Renaming temporary part tmp_insert_20220214_18232_18232_0 to 20220214_273459_273459_0.
2022.02.23 12:23:56.299218 [ 11329 ] {insert} <Error> executeQuery: Code: 107. DB::Exception: Part directory /clickhouse/data/db/table/tmp_insert_20220214_18232_18232_0/ doesn't exist. Most likely it is a logical error. (FILE_DOESNT_EXIST) (version 22.2.1.1) (from 127.1:24572) (in query: INSERT INTO db.table (...) VALUES), Stack trace (when copying this message, always include the lines below):
Follow-up for: #28760
Refs: #33291
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
