tests/query_test/test_tablesample.py

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# Tests the TABLESAMPLE clause.

import pytest

from tests.common.impala_test_suite import ImpalaTestSuite
from tests.common.test_vector import ImpalaTestDimension

class TestTableSample(ImpalaTestSuite):
  @classmethod
  def get_workload(cls):
    return 'functional-query'

  @classmethod
  def add_test_dimensions(cls):
    super(TestTableSample, cls).add_test_dimensions()
    cls.ImpalaTestMatrix.add_dimension(ImpalaTestDimension('repeatable', *[True, False]))
    # Tablesample is only supported on HDFS tables.
    cls.ImpalaTestMatrix.add_constraint(lambda v:
      v.get_value('table_format').file_format != 'kudu' and
      v.get_value('table_format').file_format != 'hbase')
    if cls.exploration_strategy() != 'exhaustive':
      # Cut down on core testing time by limiting the file formats.
      cls.ImpalaTestMatrix.add_constraint(lambda v:
        v.get_value('table_format').file_format == 'parquet' or
        v.get_value('table_format').file_format == 'text')

  def test_tablesample(self, vector):
    # Do not use a .test to avoid making this test flaky.
    # 1. Queries without the repeatable clause are non-deterministic.
    # 2. The results of queries without a repeatable clause could change due to
    # changes in data loading that affect the number or size of files.
    repeatable = vector.get_value('repeatable')
    ImpalaTestSuite.change_database(self.client, vector.get_value('table_format'))
    result = self.client.execute("select count(*) from alltypes")
    baseline_count = int(result.data[0])
    prev_count = None
    for perc in [5, 20, 50]:
      rep_sql = ""
      if repeatable: rep_sql = " repeatable(1)"
      result = self.client.execute(
        "select count(*) from alltypes tablesample system(%s)%s" % (perc, rep_sql))
      count = int(result.data[0])
      assert count < baseline_count
      if prev_count and repeatable:
        # May not necessarily be true for non-repeatable samples
        assert count > prev_count
      prev_count = count