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
The following headers are pretty generic, so use forward declaration as
much as possible:
- Context.h
- Settings.h
- ConnectionTimeouts.h
(Also this shows that some missing some includes -- this has been fixed)
And split ConnectionTimeouts.h into ConnectionTimeoutsContext.h (since
module part cannot be added for it, due to recursive build dependencies
that will be introduced)
Also remove Settings from the RemoteBlockInputStream/RemoteQueryExecutor
and just pass the context, since settings was passed only in speicifc
places, that can allow making a copy of Context (i.e. Copier).
Approx results (How much units will be recompiled after changing file X?):
- ConnectionTimeouts.h
- mainline: 100
- Context.h:
- mainline: ~800
- patched: 415
- Settings.h:
- mainline: 900-1K
- patched: 440 (most of them because of the Context.h)
Add inter-server cluster secret, it is used for Distributed queries
inside cluster, you can configure in the configuration file:
<remote_servers>
<logs>
<shard>
<secret>foobar</secret> <!-- empty -- works as before -->
...
</shard>
</logs>
</remote_servers>
And this will allow clickhouse to make sure that the query was not
faked, and was issued from the node that knows the secret. And since
trust appeared it can use initial_user for query execution, this will
apply correct *_for_user (since with inter-server secret enabled, the
query will be executed from the same user on the shards as on initator,
unlike "default" user w/o it).
v2: Change user to the initial_user for Distributed queries if secret match
v3: Add Protocol::Cluster package
v4: Drop Protocol::Cluster and use plain Protocol::Hello + user marker
v5: Do not use user from Hello for cluster-secure (superfluous)
Process query until the stage where the aggregate functions were
calculated and finalized.
It will be used for optimize_distributed_group_by_sharding_key.
v2: fix aliases
v3: Fix protocol ABI breakage due to WithMergeableStateAfterAggregation
Conditions >= for QueryProcessingStage::Enum has been verified, and they
are ok (in InterpreterSelectQuery).
