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Change DB utils behavior when a truncated row is found to only drop the row #7983

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merged 2 commits into from
Nov 10, 2020
Merged

Change DB utils behavior when a truncated row is found to only drop the row #7983

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03c0b03
Change behavior when a truncated row is found to only drop the row
justiniso Nov 9, 2020
9beb3e0
Fix truncation tests
justiniso Nov 9, 2020
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17 changes: 5 additions & 12 deletions datadog_checks_base/datadog_checks/base/utils/db/statement_metrics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,6 @@ def compute_derivative_rows(self, rows, metrics, key):
"""
result = []
new_cache = {}
negative_result_found = False
metrics = set(metrics)

if len(rows) > 0:
Expand All @@ -68,11 +67,6 @@ def compute_derivative_rows(self, rows, metrics, key):
# whether a metric is submitted for the row during this run or not.
new_cache[row_key] = row

# If a stats reset has happened, all other logic can be skipped since the previous check run's values are
# invalidated.
if negative_result_found:
continue

prev = self._previous_statements.get(row_key)
if prev is None:
continue
Expand All @@ -83,8 +77,8 @@ def compute_derivative_rows(self, rows, metrics, key):
# There are a couple of edge cases to be aware of:
#
# 1. Table truncation or stats reset: Because the table values are always increasing, a negative value
# suggests truncation or a stats reset. In this case, all rows from the previous run must be discarded.
# Tracking should start over with the current run's values.
# suggests truncation or a stats reset. In this case, the row difference is discarded and the row should.
# be tracked from this run forward.
#
# 2. No changes since the previous run: There is no need to store metrics of 0, since that is implied by
# the absence of metrics. On any given check run, most rows will have no difference so this optimization
Expand All @@ -94,7 +88,9 @@ def compute_derivative_rows(self, rows, metrics, key):

# Check for negative values, but only in the columns used for metrics
if any(diffed_row[k] < 0 for k in metric_columns):
negative_result_found = True
# A "break" might be expected here instead of "continue," but there are cases where a subset of rows
# are removed. To avoid situations where all results are discarded every check run, we err on the side
# of potentially including truncated rows that exceed previous run counts.
continue

# No changes to the query; no metric needed
Expand All @@ -105,9 +101,6 @@ def compute_derivative_rows(self, rows, metrics, key):

self._previous_statements = new_cache

if negative_result_found:
return []

return result


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10 changes: 5 additions & 5 deletions datadog_checks_base/tests/test_db_statements.py
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Original file line number Diff line number Diff line change
Expand Up @@ -97,17 +97,17 @@ def key(row):
]
# Simulate a stats reset by decreasing one of the metrics rather than increasing
rows3 = [
add_to_dict(rows2[1], {'count': 1, 'time': 15, 'errors': 0}),
add_to_dict(rows2[0], {'count': -1, 'time': 0, 'errors': 15}),
add_to_dict(rows2[1], {'count': 1, 'time': 15, 'errors': 0}),
]
rows4 = [
add_to_dict(rows3[1], {'count': 1, 'time': 1, 'errors': 0}),
add_to_dict(rows3[0], {'count': 1, 'time': 1, 'errors': 1}),
add_to_dict(rows3[1], {'count': 1, 'time': 1, 'errors': 0}),
]
assert [] == sm.compute_derivative_rows(rows1, metrics, key=key)
assert 2 == len(sm.compute_derivative_rows(rows2, metrics, key=key))
assert [] == sm.compute_derivative_rows(rows3, metrics, key=key)
assert 2 == len(sm.compute_derivative_rows(rows4, metrics, key=key))
assert 2 == len(sm.compute_derivative_rows(rows2, metrics, key=key)) # both rows computed
assert 1 == len(sm.compute_derivative_rows(rows3, metrics, key=key)) # only 1 row computed
assert 2 == len(sm.compute_derivative_rows(rows4, metrics, key=key)) # both rows computed

def test_apply_row_limits(self):
def assert_any_order(a, b):
Expand Down