Recently I saw the following, the client executed long distributed query
and terminated the connection, and in this case query cancellation will
be done from PullingAsyncPipelineExecutor dtor, but during cancellation
one of nodes sent ECONNRESET, and this leads to an exception from
PullingAsyncPipelineExecutor::cancel(), and this leads to a deadlock
when multiple threads waits each others, because cancel() for
LazyOutputFormat wasn't called.
Here is as relevant portion of logs:
2023.01.04 08:26:09.236208 [ 37968 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Debug> executeQuery: (from 10.61.13.253:44266, user: default) TooLongDistributedQueryToPost
...
2023.01.04 08:26:09.262424 [ 37968 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Trace> MergeTreeInOrderSelectProcessor: Reading 1 ranges in order from part 9_330_538_18, approx. 61440 rows starting from 0
2023.01.04 08:26:09.266399 [ 26788 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Trace> Connection (s4.ch:9000): Connecting. Database: (not specified). User: default
2023.01.04 08:26:09.266849 [ 26788 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Trace> Connection (s4.ch:9000): Connected to ClickHouse server version 22.10.1.
2023.01.04 08:26:09.267165 [ 26788 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Debug> Connection (s4.ch:9000): Sent data for 2 scalars, total 2 rows in 3.1587e-05 sec., 62635 rows/sec., 68.00 B (2.03 MiB/sec.), compressed 0.4594594594594595 times to 148.00 B (4.41 MiB/sec.)
2023.01.04 08:39:13.047170 [ 37968 ] {f2ed6149-146d-4a3d-874a-b0b751c7b567} <Error> PullingAsyncPipelineExecutor: Code: 210. DB::NetException: Connection reset by peer, while writing to socket (10.7.142.115:9000). (NETWORK_ERROR), Stack trace (when copying this message, always include the lines below):
0. ./.build/./contrib/libcxx/include/exception:133: Poco::Exception::Exception(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int) @ 0x1818234c in /usr/lib/debug/usr/bin/clickhouse.debug
1. ./.build/./src/Common/Exception.cpp:69: DB::Exception::Exception(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int, bool) @ 0x1004fbda in /usr/lib/debug/usr/bin/clickhouse.debug
2. ./.build/./src/Common/NetException.h:12: DB::WriteBufferFromPocoSocket::nextImpl() @ 0x14e352f3 in /usr/lib/debug/usr/bin/clickhouse.debug
3. ./.build/./src/IO/BufferBase.h:39: DB::Connection::sendCancel() @ 0x15c21e6b in /usr/lib/debug/usr/bin/clickhouse.debug
4. ./.build/./src/Client/MultiplexedConnections.cpp:0: DB::MultiplexedConnections::sendCancel() @ 0x15c4d5b7 in /usr/lib/debug/usr/bin/clickhouse.debug
5. ./.build/./src/QueryPipeline/RemoteQueryExecutor.cpp:627: DB::RemoteQueryExecutor::tryCancel(char const*, std::__1::unique_ptr<DB::RemoteQueryExecutorReadContext, std::__1::default_delete<DB::RemoteQueryExecutorReadContext> >*) @ 0x14446c09 in /usr/lib/debug/usr/bin/clickhouse.debug
6. ./.build/./contrib/libcxx/include/__iterator/wrap_iter.h💯 DB::ExecutingGraph::cancel() @ 0x15d2c0de in /usr/lib/debug/usr/bin/clickhouse.debug
7. ./.build/./contrib/libcxx/include/__memory/unique_ptr.h:300: DB::PullingAsyncPipelineExecutor::cancel() @ 0x15d32055 in /usr/lib/debug/usr/bin/clickhouse.debug
8. ./.build/./contrib/libcxx/include/__memory/unique_ptr.h:312: DB::PullingAsyncPipelineExecutor::~PullingAsyncPipelineExecutor() @ 0x15d31f4f in /usr/lib/debug/usr/bin/clickhouse.debug
9. ./.build/./src/Server/TCPHandler.cpp:0: DB::TCPHandler::processOrdinaryQueryWithProcessors() @ 0x15cde919 in /usr/lib/debug/usr/bin/clickhouse.debug
10. ./.build/./src/Server/TCPHandler.cpp:0: DB::TCPHandler::runImpl() @ 0x15cd8554 in /usr/lib/debug/usr/bin/clickhouse.debug
11. ./.build/./src/Server/TCPHandler.cpp:1904: DB::TCPHandler::run() @ 0x15ce6479 in /usr/lib/debug/usr/bin/clickhouse.debug
12. ./.build/./contrib/poco/Net/src/TCPServerConnection.cpp:57: Poco::Net::TCPServerConnection::start() @ 0x18074f07 in /usr/lib/debug/usr/bin/clickhouse.debug
13. ./.build/./contrib/libcxx/include/__memory/unique_ptr.h:54: Poco::Net::TCPServerDispatcher::run() @ 0x180753ed in /usr/lib/debug/usr/bin/clickhouse.debug
14. ./.build/./contrib/poco/Foundation/src/ThreadPool.cpp:213: Poco::PooledThread::run() @ 0x181e3807 in /usr/lib/debug/usr/bin/clickhouse.debug
15. ./.build/./contrib/poco/Foundation/include/Poco/SharedPtr.h:156: Poco::ThreadImpl::runnableEntry(void*) @ 0x181e1483 in /usr/lib/debug/usr/bin/clickhouse.debug
16. ? @ 0x7ffff7e55fd4 in ?
17. ? @ 0x7ffff7ed666c in ?
(version 22.10.1.1)
And here is the state of the threads:
<details>
<summary>system.stack_trace</summary>
```sql
SELECT
arrayStringConcat(arrayMap(x -> demangle(addressToSymbol(x)), trace), '\n') AS sym
FROM system.stack_trace
WHERE query_id = 'f2ed6149-146d-4a3d-874a-b0b751c7b567'
SETTINGS allow_introspection_functions=1
Row 1:
──────
sym:
pthread_cond_wait
std::__1::condition_variable::wait(std::__1::unique_lock<std::__1::mutex>&)
bool ConcurrentBoundedQueue<DB::Chunk>::emplaceImpl<DB::Chunk>(std::__1::optional<unsigned long>, DB::Chunk&&)
DB::IOutputFormat::work()
DB::ExecutionThreadContext::executeTask()
DB::PipelineExecutor::executeStepImpl(unsigned long, std::__1::atomic<bool>*)
Row 2:
──────
sym:
pthread_cond_wait
Poco::EventImpl::waitImpl()
DB::PipelineExecutor::joinThreads()
DB::PipelineExecutor::executeImpl(unsigned long)
DB::PipelineExecutor::execute(unsigned long)
Row 3:
──────
sym:
pthread_cond_wait
Poco::EventImpl::waitImpl()
DB::PullingAsyncPipelineExecutor::Data::~Data()
DB::PullingAsyncPipelineExecutor::~PullingAsyncPipelineExecutor()
DB::TCPHandler::processOrdinaryQueryWithProcessors()
DB::TCPHandler::runImpl()
DB::TCPHandler::run()
Poco::Net::TCPServerConnection::start()
Poco::Net::TCPServerDispatcher::run()
Poco::PooledThread::run()
Poco::ThreadImpl::runnableEntry(void*)
```
</details>
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
Reasons:
1. The original Gorilla paper proposed a compression schema for pairs of
time stamps and double-precision FP values. ClickHouse's Gorilla
codec only implements compression of the latter and it does not
impose any data type restrictions.
- Data types != Float* or (U)Int* (e.g. Decimal, Point etc.) are
definitely not supposed to be used with Gorilla.
- (U)Int* types are debatable. The paper only considers
integers-stored-as-FP-values, a practical use case for which
Gorilla works well. Standalone integers are not considered which
makes them at least suspicious.
2. Achieve consistency with FPC, another specialized floating-point
timeseries codec, which rejects non-float data.
3. On practical datasets, ZSTD is often "good enough" (**) so it should
be okay to disincentive non-ZSTD codecs a little bit. If needed,
Delta and DoubleDelta codecs are viable alternative for slowly
changing (time-series-like) integer sequences.
Since on-prem and hosted users may still have Gorilla-compressed
non-float data, this combination is only deprecated for now. No warning
or error will be emitted. Users are encouraged to migrate
Gorilla-compressed non-float data to an alternative codec. It is planned
to treat Gorilla-compressed non-float columns as "suspicious" six months
after this commit (i.e. in v23.6). Even then, it will still be possible
to set "allow_suspicious_codecs = true" and read and write
Gorilla-compressed non-float data.
(*) Sec. 4.1.2, "Gorilla restricts the value element in its tuple to a
double floating point type.", https://doi.org/10.14778/2824032.2824078
(**) https://clickhouse.com/blog/optimize-clickhouse-codecs-compression-schema
