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
Logging from PushingToViewsBlockOutputStream::write() is incorrect,
since it does not takes into account squashing (default to 1<<20 rows
and 256<<20), whle write will be done from
PushingToViewsBlockOutputStream::writeSuffix().
Fixes: #19378
* add the query data deduplication excluding duplicated parts in MergeTree family engines.
query deduplication is based on parts' UUID which should be enabled first with merge_tree setting
assign_part_uuids=1
allow_experimental_query_deduplication setting is to enable part deduplication, default ot false.
data part UUID is a mechanism of giving a data part a unique identifier.
Having UUID and deduplication mechanism provides a potential of moving parts
between shards preserving data consistency on a read path:
duplicated UUIDs will cause root executor to retry query against on of the replica explicitly
asking to exclude encountered duplicated fingerprints during a distributed query execution.
NOTE: this implementation don't provide any knobs to lock part and hence its UUID. Any mutations/merge will
update part's UUID.
* add _part_uuid virtual column, allowing to use UUIDs in predicates.
Signed-off-by: Aleksei Semiglazov <asemiglazov@cloudflare.com>
address comments
Since right now theses queries are not logged and there is no way to
determine the time that it takes.
Proper fix will be to account them in system.processes (and all other
places), but this is not that easy.
