The following should happens before:
- incorrect shards was selected
- "Cannot infer type of an empty tuple" exception for empty tuple() for localhost
- "Function tuple requires at least one argument" exception for empty tuple() for remote node
This way the remote nodes will not need to send all the rows, so this
will decrease network io and also this will make queries w/
optimize_aggregation_in_order=1/LIMIT X and w/o ORDER BY faster since it
initiator will not need to read all the rows, only first X (but note
that for this you need to your data to be sharded correctly or you may
get inaccurate results).
Note, that having lots of processing stages will increase the complexity
of interpreter (it is already not that clean and simple right now).
Although using separate QueryProcessingStage looks pretty natural.
Another option is to make WithMergeableStateAfterAggregation always, but
in this case you will not be able to disable only this optimization,
i.e. if there will be some issue with it.
v2: fix OFFSET
v3: convert 01814_distributed_push_down_limit test to .sh and add retries
v4: add test with OFFSET
v5: add new query stage into the bash completion
v6/tests: use LIMIT O,L syntax over LIMIT L OFFSET O since it is broken in ANTLR parser
https://clickhouse-test-reports.s3.yandex.net/23027/a18a06399b7aeacba7c50b5d1e981ada5df19745/functional_stateless_tests_(antlr_debug).html#fail1
v7/tests: set use_hedged_requests to 0, to avoid excessive log entries on retries
https://clickhouse-test-reports.s3.yandex.net/23027/a18a06399b7aeacba7c50b5d1e981ada5df19745/functional_stateless_tests_flaky_check_(address).html#fail1
Before this patch (and after #22208) the INSERT may fail with "Cannot
schedule a task" because the pool in DistributedBlockOutputStream
already throws exception and simply fail in writeSuffix().
INSERT into Distributed with insert_distributed_sync=1 stores the
distributed batches on the disk for sending in background.
But types may be a little bit different for the Distributed and it's
underlying table, so the initiator need to know whether conversion is
required or not.
Before this patch those on disk distributed batches contains header,
which includes dumpStructure() for the block in that batch, however it
checks not only names and types and plus dumpStructure() is a debug
method.
So instead of storing string representation for the block header we
should store empty block in the file header (note, that we cannot store
the empty block not in header, since this will require reading all
blocks from file, due to some trickery of the readers interface).
Note, that this patch also contains tiny refactoring:
- s/header/distributed_header/
v1: dumpNamesAndTypes()
v2: dump empty block into the batch itself
v3: move empty block into the header
