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Syntax: <tableref> TABLESAMPLE SYSTEM(<number>) [REPEATABLE(<number>)] The first number specifies the percent of table bytes to sample. The second number specifies the random seed to use. The sampling is coarse-grained. Impala keeps randomly adding files to the sample until at least the desired percentage of file bytes have been reached. Examples: SELECT * FROM t TABLESAMPLE SYSTEM(10) SELECT * FROM t TABLESAMPLE SYSTEM(50) REPEATABLE(1234) Testing: - Added parser, analyser, planner, and end-to-end tests - Private core/hdfs run passed Change-Id: Ief112cfb1e4983c5d94c08696dc83da9ccf43f70 Reviewed-on: http://gerrit.cloudera.org:8080/6868 Reviewed-by: Alex Behm <alex.behm@cloudera.com> Tested-by: Impala Public Jenkins
65 lines
2.7 KiB
Python
65 lines
2.7 KiB
Python
# Licensed to the Apache Software Foundation (ASF) under one
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# or more contributor license agreements. See the NOTICE file
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# distributed with this work for additional information
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# regarding copyright ownership. The ASF licenses this file
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# to you under the Apache License, Version 2.0 (the
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# "License"); you may not use this file except in compliance
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# with the License. You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing,
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# software distributed under the License is distributed on an
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# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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# KIND, either express or implied. See the License for the
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# specific language governing permissions and limitations
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# under the License.
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# Tests the TABLESAMPLE clause.
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import pytest
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from tests.common.impala_test_suite import ImpalaTestSuite
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from tests.common.test_vector import ImpalaTestDimension
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class TestTableSample(ImpalaTestSuite):
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@classmethod
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def get_workload(cls):
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return 'functional-query'
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@classmethod
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def add_test_dimensions(cls):
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super(TestTableSample, cls).add_test_dimensions()
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cls.ImpalaTestMatrix.add_dimension(ImpalaTestDimension('repeatable', *[True, False]))
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# Tablesample is only supported on HDFS tables.
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cls.ImpalaTestMatrix.add_constraint(lambda v:
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v.get_value('table_format').file_format != 'kudu' and
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v.get_value('table_format').file_format != 'hbase')
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if cls.exploration_strategy() != 'exhaustive':
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# Cut down on core testing time by limiting the file formats.
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cls.ImpalaTestMatrix.add_constraint(lambda v:
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v.get_value('table_format').file_format == 'parquet' or
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v.get_value('table_format').file_format == 'text')
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def test_tablesample(self, vector):
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# Do not use a .test to avoid making this test flaky.
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# 1. Queries without the repeatable clause are non-deterministic.
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# 2. The results of queries without a repeatable clause could change due to
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# changes in data loading that affect the number or size of files.
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repeatable = vector.get_value('repeatable')
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ImpalaTestSuite.change_database(self.client, vector.get_value('table_format'))
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result = self.client.execute("select count(*) from alltypes")
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baseline_count = int(result.data[0])
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prev_count = None
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for perc in [5, 20, 50]:
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rep_sql = ""
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if repeatable: rep_sql = " repeatable(1)"
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result = self.client.execute(
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"select count(*) from alltypes tablesample system(%s)%s" % (perc, rep_sql))
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count = int(result.data[0])
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assert count < baseline_count
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if prev_count and repeatable:
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# May not necessarily be true for non-repeatable samples
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assert count > prev_count
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prev_count = count
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