Since this hides real problems, since destructor does final flush and if
it fails, then data will be lost.
One of such examples if MEMORY_LIMIT_EXCEEDED exception, so lock
exceptions from destructors, by using
MemoryTracker::LockExceptionInThread to block these exception, and allow
others (so std::terminate will be called, since this is c++11 with
noexcept for destructors by default).
Here is an example, that leads to empty block in the distributed batch:
2021.01.21 12:43:18.619739 [ 46468 ] {7bd60d75-ebcb-45d2-874d-260df9a4ddac} <Error> virtual DB::CompressedWriteBuffer::~CompressedWriteBuffer(): Code: 241, e.displayText() = DB::Exception: Memory limit (for user) exceeded: would use 332.07 GiB (attempt to allocate chunk of 4355342 bytes), maximum: 256.00 GiB, Stack trace (when copying this message, always include the lines below):
0. DB::Exception::Exception<>() @ 0x86f7b88 in /usr/bin/clickhouse
...
4. void DB::PODArrayBase<>::resize<>(unsigned long) @ 0xe9e878d in /usr/bin/clickhouse
5. DB::CompressedWriteBuffer::nextImpl() @ 0xe9f0296 in /usr/bin/clickhouse
6. DB::CompressedWriteBuffer::~CompressedWriteBuffer() @ 0xe9f0415 in /usr/bin/clickhouse
7. DB::DistributedBlockOutputStream::writeToShard() @ 0xf6bed4a in /usr/bin/clickhouse
The MySQL replication code assumed that row update events would be
preceded by a single TABLE_MAP_EVENT. However, if a single SQL
statement modifies rows in multiple tables, MySQL will first send
table map events for all involved tables, and then row update events.
Depending on circumstances, this could lead to an exception when the row
update was processed, the update could be incorrectly dropped, or the
update could be applied to the wrong table.