Merge pull request #82289 from michae2/backport22.1-81793

release-22.1: sql/stats: store non-NULL histograms for empty tables
cockroachdb · Jun 1, 2022 · 97d0c6e · 97d0c6e
2 parents e8a6bed + c23e622
commit 97d0c6e
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Showing 5 changed files with 205 additions and 3 deletions.
diff --git a/pkg/sql/logictest/testdata/logic_test/distsql_stats b/pkg/sql/logictest/testdata/logic_test/distsql_stats
@@ -1222,6 +1222,7 @@ FROM [SHOW STATISTICS USING JSON FOR TABLE all_null]
         ],
         "distinct_count": 1,
         "histo_col_type": "INT8",
+        "histo_version": 1,
         "name": "s",
         "null_count": 1,
         "row_count": 1
@@ -1348,3 +1349,196 @@ CREATE TABLE t76867 (
 
 statement ok
 ANALYZE t76867
+
+# Collecting stats on empty tables should result in empty (but not NULL)
+# histograms.
+statement ok
+CREATE TABLE tabula (r INT, a INT, sa INT, PRIMARY KEY (r), INDEX (a, sa))
+
+statement ok
+CREATE STATISTICS aristotle FROM tabula
+
+query TTIB colnames
+SELECT statistics_name, column_names, row_count, histogram_id IS NOT NULL AS has_histogram
+FROM [SHOW STATISTICS FOR TABLE tabula]
+ORDER BY statistics_name, column_names::STRING
+----
+statistics_name  column_names  row_count  has_histogram
+aristotle        {a,sa}        0          false
+aristotle        {a}           0          true
+aristotle        {r}           0          true
+aristotle        {sa}          0          true
+
+let $hist_id_1
+SELECT histogram_id FROM [SHOW STATISTICS FOR TABLE tabula]
+WHERE statistics_name = 'aristotle' AND column_names = '{a}'
+
+# This histogram should be empty.
+query TIRI colnames
+SHOW HISTOGRAM $hist_id_1
+----
+upper_bound  range_rows  distinct_range_rows  equal_rows
+
+query T
+SELECT jsonb_pretty(COALESCE(json_agg(stat), '[]'))
+  FROM (SELECT json_array_elements(statistics) - 'created_at' AS stat
+        FROM [SHOW STATISTICS USING JSON FOR TABLE tabula])
+----
+[
+    {
+        "avg_size": 0,
+        "columns": [
+            "r"
+        ],
+        "distinct_count": 0,
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "aristotle",
+        "null_count": 0,
+        "row_count": 0
+    },
+    {
+        "avg_size": 0,
+        "columns": [
+            "a"
+        ],
+        "distinct_count": 0,
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "aristotle",
+        "null_count": 0,
+        "row_count": 0
+    },
+    {
+        "avg_size": 0,
+        "columns": [
+            "sa"
+        ],
+        "distinct_count": 0,
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "aristotle",
+        "null_count": 0,
+        "row_count": 0
+    },
+    {
+        "avg_size": 0,
+        "columns": [
+            "a",
+            "sa"
+        ],
+        "distinct_count": 0,
+        "histo_col_type": "",
+        "name": "aristotle",
+        "null_count": 0,
+        "row_count": 0
+    }
+]
+
+# Collecting stats on columns with all NULL values should also result in empty
+# (but not NULL) histograms.
+statement ok
+INSERT INTO tabula VALUES (11, 12, NULL)
+
+statement ok
+CREATE STATISTICS locke FROM tabula
+
+query TTIIB colnames
+SELECT statistics_name, column_names, row_count, null_count, histogram_id IS NOT NULL AS has_histogram
+FROM [SHOW STATISTICS FOR TABLE tabula]
+ORDER BY statistics_name, column_names::STRING
+----
+statistics_name  column_names  row_count  null_count  has_histogram
+locke            {a,sa}        1          0           false
+locke            {a}           1          0           true
+locke            {r}           1          0           true
+locke            {sa}          1          1           true
+
+let $hist_id_1
+SELECT histogram_id FROM [SHOW STATISTICS FOR TABLE tabula]
+WHERE statistics_name = 'locke' AND column_names = '{a}'
+
+# This histogram should *not* be empty.
+query TIRI colnames
+SHOW HISTOGRAM $hist_id_1
+----
+upper_bound  range_rows  distinct_range_rows  equal_rows
+12           0           0                    1
+
+let $hist_id_1
+SELECT histogram_id FROM [SHOW STATISTICS FOR TABLE tabula]
+WHERE statistics_name = 'locke' AND column_names = '{sa}'
+
+# This histogram *should* be empty.
+query TIRI colnames
+SHOW HISTOGRAM $hist_id_1
+----
+upper_bound  range_rows  distinct_range_rows  equal_rows
+
+query T
+SELECT jsonb_pretty(COALESCE(json_agg(stat), '[]'))
+  FROM (SELECT json_array_elements(statistics) - 'created_at' - 'avg_size' AS stat
+        FROM [SHOW STATISTICS USING JSON FOR TABLE tabula])
+----
+[
+    {
+        "columns": [
+            "r"
+        ],
+        "distinct_count": 1,
+        "histo_buckets": [
+            {
+                "distinct_range": 0,
+                "num_eq": 1,
+                "num_range": 0,
+                "upper_bound": "11"
+            }
+        ],
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "locke",
+        "null_count": 0,
+        "row_count": 1
+    },
+    {
+        "columns": [
+            "a"
+        ],
+        "distinct_count": 1,
+        "histo_buckets": [
+            {
+                "distinct_range": 0,
+                "num_eq": 1,
+                "num_range": 0,
+                "upper_bound": "12"
+            }
+        ],
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "locke",
+        "null_count": 0,
+        "row_count": 1
+    },
+    {
+        "columns": [
+            "sa"
+        ],
+        "distinct_count": 1,
+        "histo_col_type": "INT8",
+        "histo_version": 1,
+        "name": "locke",
+        "null_count": 1,
+        "row_count": 1
+    },
+    {
+        "columns": [
+            "a",
+            "sa"
+        ],
+        "distinct_count": 1,
+        "histo_col_type": "",
+        "name": "locke",
+        "null_count": 0,
+        "row_count": 1
+    }
+]
diff --git a/pkg/sql/rowexec/sample_aggregator.go b/pkg/sql/rowexec/sample_aggregator.go
@@ -434,7 +434,7 @@ func (s *sampleAggregator) writeResults(ctx context.Context) error {
 	if err := s.FlowCtx.Cfg.DB.Txn(ctx, func(ctx context.Context, txn *kv.Txn) error {
 		for _, si := range s.sketches {
 			var histogram *stats.HistogramData
-			if si.spec.GenerateHistogram && len(s.sr.Get()) != 0 {
+			if si.spec.GenerateHistogram {
 				colIdx := int(si.spec.Columns[0])
 				typ := s.inTypes[colIdx]
 

diff --git a/pkg/sql/stats/histogram.go b/pkg/sql/stats/histogram.go
@@ -86,7 +86,9 @@ func EquiDepthHistogram(
 ) (HistogramData, []cat.HistogramBucket, error) {
 	numSamples := len(samples)
 	if numSamples == 0 {
-		return HistogramData{ColumnType: colType}, nil, nil
+		return HistogramData{
+			ColumnType: colType, Buckets: make([]HistogramData_Bucket, 0), Version: histVersion,
+		}, nil, nil
 	}
 	if maxBuckets < 2 {
 		return HistogramData{}, nil, errors.Errorf("histogram requires at least two buckets")

diff --git a/pkg/sql/stats/histogram_test.go b/pkg/sql/stats/histogram_test.go
@@ -244,6 +244,12 @@ func TestEquiDepthHistogram(t *testing.T) {
 			if err != nil {
 				t.Fatal(err)
 			}
+			if h.Version != histVersion {
+				t.Errorf("Invalid histogram version %d expected %d", h.Version, histVersion)
+			}
+			if (h.Buckets == nil) != (tc.buckets == nil) {
+				t.Fatalf("Invalid bucket == nil: %v, expected %v", h.Buckets == nil, tc.buckets == nil)
+			}
 			if len(h.Buckets) != len(tc.buckets) {
 				t.Fatalf("Invalid number of buckets %d, expected %d", len(h.Buckets), len(tc.buckets))
 			}

diff --git a/pkg/sql/stats/json.go b/pkg/sql/stats/json.go
@@ -129,7 +129,7 @@ func (js *JSONStatistic) DecodeAndSetHistogram(
 func (js *JSONStatistic) GetHistogram(
 	semaCtx *tree.SemaContext, evalCtx *tree.EvalContext,
 ) (*HistogramData, error) {
-	if len(js.HistogramBuckets) == 0 {
+	if js.HistogramColumnType == "" {
 		return nil, nil
 	}
 	h := &HistogramData{}