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Merge pull request #16675 from ClickHouse/max_parallel_replicas_without_sampling

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Fix 'max_parallel_replicas' without sampling.
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alexey-milovidov 2020-11-05 12:16:23 +03:00 committed by GitHub
commit 5d8844b66e
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4 changed files with 36 additions and 0 deletions
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9
src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp
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@ -366,6 +366,15 @@ Pipe MergeTreeDataSelectExecutor::readFromParts(
* It is also important that the entire universe can be covered using SAMPLE 0.1 OFFSET 0, ... OFFSET 0.9 and similar decimals.
*/
/// Parallel replicas has been requested but there is no way to sample data.
/// Select all data from first replica and no data from other replicas.
if (settings.parallel_replicas_count > 1 && !data.supportsSampling() && settings.parallel_replica_offset > 0)
{
LOG_DEBUG(log, "Will use no data on this replica because parallel replicas processing has been requested"
" (the setting 'max_parallel_replicas') but the table does not support sampling and this replica is not the first.");
return {};
}
bool use_sampling = relative_sample_size > 0 || (settings.parallel_replicas_count > 1 && data.supportsSampling());
bool no_data = false; /// There is nothing left after sampling.

4
tests/queries/0_stateless/01557_max_parallel_replicas_no_sample.reference Normal file
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@ -0,0 +1,4 @@
Hello
1000
1000
1000

22
tests/queries/0_stateless/01557_max_parallel_replicas_no_sample.sql Normal file
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@ -0,0 +1,22 @@
DROP TABLE IF EXISTS t;
CREATE TABLE t (x String) ENGINE = MergeTree ORDER BY x;
INSERT INTO t VALUES ('Hello');
SET max_parallel_replicas = 3;
SELECT * FROM remote('127.0.0.{2|3|4}', currentDatabase(), t);
DROP TABLE t;
CREATE TABLE t (x String) ENGINE = MergeTree ORDER BY cityHash64(x) SAMPLE BY cityHash64(x);
INSERT INTO t SELECT toString(number) FROM numbers(1000);
SET max_parallel_replicas = 1;
SELECT count() FROM remote('127.0.0.{2|3|4}', currentDatabase(), t);
SET max_parallel_replicas = 2;
SELECT count() FROM remote('127.0.0.{2|3|4}', currentDatabase(), t);
SET max_parallel_replicas = 3;
SELECT count() FROM remote('127.0.0.{2|3|4}', currentDatabase(), t);
DROP TABLE t;

1
tests/queries/0_stateless/arcadia_skip_list.txt
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@ -159,3 +159,4 @@
01547_query_log_current_database
01548_query_log_query_execution_ms
01552_dict_fixedstring
01557_max_parallel_replicas_no_sample.sql