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sql/stats: remove NumRange-stealing behavior from histogram prediction #86348

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Aug 18, 2022
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sql/stats: remove NumRange-stealing behavior from histogram prediction #86348

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139 changes: 138 additions & 1 deletion pkg/sql/opt/exec/execbuilder/testdata/forecast
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Original file line number Diff line number Diff line change
Expand Up @@ -592,8 +592,145 @@ scan c
├── columns: h:1
├── constraint: /1: [/'1988-08-07 00:00:00+00:00' - ]
├── stats: [rows=24, distinct(1)=24, null(1)=0, avgsize(1)=7]
│ histogram(1)= 0 1 5 1 5 1 5 1 4 1
│ histogram(1)= 0 1 5 1 5 1 5 1 5 0
│ <--- '1988-08-07 00:00:00+00:00' --- '1988-08-07 06:00:00+00:00' --- '1988-08-07 12:00:00+00:00' --- '1988-08-07 18:00:00+00:00' --- '1988-08-08 00:00:00+00:00'
├── cost: 39.7
├── key: (1)
└── distribution: test

# Test for issue 86344.

statement ok
CREATE TABLE x (a INT PRIMARY KEY) WITH (sql_stats_automatic_collection_enabled = false);

statement ok
ALTER TABLE x INJECT STATISTICS '[
{
"avg_size": 1,
"columns": [
"a"
],
"created_at": "2020-03-13 00:00:00.000000",
"distinct_count": 4,
"histo_buckets": [
{
"distinct_range": 0,
"num_eq": 0,
"num_range": 0,
"upper_bound": "4"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "7"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "10"
}
],
"histo_col_type": "INT8",
"histo_version": 2,
"name": "__auto__",
"null_count": 0,
"row_count": 4
},
{
"avg_size": 1,
"columns": [
"a"
],
"created_at": "2020-03-14 00:00:00.000000",
"distinct_count": 4,
"histo_buckets": [
{
"distinct_range": 0,
"num_eq": 0,
"num_range": 0,
"upper_bound": "7"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "10"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "13"
}
],
"histo_col_type": "INT8",
"histo_version": 2,
"name": "__auto__",
"null_count": 0,
"row_count": 4
},
{
"avg_size": 1,
"columns": [
"a"
],
"created_at": "2020-03-15 00:00:00.000000",
"distinct_count": 4,
"histo_buckets": [
{
"distinct_range": 0,
"num_eq": 0,
"num_range": 0,
"upper_bound": "10"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "13"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "16"
}
],
"histo_col_type": "INT8",
"histo_version": 2,
"name": "__auto__",
"null_count": 0,
"row_count": 4
}
]';

query T
SELECT jsonb_pretty(stat->'histo_buckets')
FROM (
SELECT jsonb_array_elements(statistics) AS stat
FROM [SHOW STATISTICS USING JSON FOR TABLE x WITH FORECAST]
)
WHERE stat->>'name' = '__forecast__';
----
[
{
"distinct_range": 0,
"num_eq": 0,
"num_range": 0,
"upper_bound": "13"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "16"
},
{
"distinct_range": 2,
"num_eq": 0,
"num_range": 2,
"upper_bound": "19"
}
]
10 changes: 5 additions & 5 deletions pkg/sql/stats/forecast_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -490,22 +490,22 @@ func TestForecastColumnStatistics(t *testing.T) {
hist: testHistogram{},
},
{
at: 2, row: 5, dist: 2, null: 3, size: 2,
at: 2, row: 5, dist: 3, null: 3, size: 2,
hist: testHistogram{{1, 0, 0, 200}, {0, 1, 1, 800}},
},
{
at: 3, row: 7, dist: 3, null: 3, size: 2,
at: 3, row: 7, dist: 4, null: 3, size: 2,
hist: testHistogram{{2, 0, 0, 200}, {0, 2, 2, 800}},
},
{
at: 4, row: 9, dist: 4, null: 3, size: 2,
at: 4, row: 9, dist: 5, null: 3, size: 2,
hist: testHistogram{{3, 0, 0, 200}, {0, 3, 3, 800}},
},
},
at: 5,
forecast: &testStat{
at: 5, row: 11, dist: 5, null: 3, size: 2,
hist: testHistogram{{4, 0, 0, 200}, {1, 3, 2, 800}},
at: 5, row: 11, dist: 6, null: 3, size: 2,
hist: testHistogram{{4, 0, 0, 200}, {0, 4, 4, 800}},
},
},
// Histogram, constant numbers but changing shape
Expand Down
9 changes: 0 additions & 9 deletions pkg/sql/stats/quantile.go
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Expand Up @@ -282,15 +282,6 @@ func (q quantile) toHistogram(colType *types.T, rowCount float64) (histogram, er
if !isValidCount(numEq) {
return errors.AssertionFailedf("invalid histogram NumEq: %v", numEq)
}
if numEq < 1 && currentBucket.NumRange+numEq >= 2 {
// Steal from NumRange so that NumEq is at least 1, if it wouldn't make
// NumRange 0. This makes the histogram look more like something
// EquiDepthHistogram would produce.
// TODO(michae2): Consider removing this logic if statistics_builder
// doesn't need it.
currentBucket.NumRange -= 1 - numEq
numEq = 1
}
currentBucket.NumEq = numEq

// Calculate DistinctRange for this bucket now that NumRange is finalized.
Expand Down
16 changes: 8 additions & 8 deletions pkg/sql/stats/quantile_test.go
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Expand Up @@ -479,9 +479,9 @@ func TestQuantileToHistogram(t *testing.T) {
hist: testHistogram{{0, 0, 0, 0}, {1, 1, 1, 100}},
},
{
qfun: quantile{{0, 0}, {0.9, 100}, {1, 100}},
rows: 10,
hist: testHistogram{{0, 0, 0, 0}, {1, 9, 9, 100}},
qfun: quantile{{0, 0}, {0.9375, 100}, {1, 100}},
rows: 16,
hist: testHistogram{{0, 0, 0, 0}, {1, 15, 15, 100}},
},
{
qfun: quantile{{0, 100}, {0.25, 100}, {0.75, 200}, {1, 200}},
Expand All @@ -503,26 +503,26 @@ func TestQuantileToHistogram(t *testing.T) {
rows: 32,
hist: testHistogram{{4, 0, 0, 310}, {4, 0, 0, 320}, {8, 0, 0, 330}, {4, 0, 0, 340}, {4, 0, 0, 350}, {4, 0, 0, 360}, {4, 0, 0, 370}},
},
// Cases where we steal a row from NumRange to give to NumEq.
// Cases with 0 NumEq.
{
qfun: quantile{{0, 0}, {1, 100}},
rows: 2,
hist: testHistogram{{0, 0, 0, 0}, {1, 1, 1, 100}},
hist: testHistogram{{0, 0, 0, 0}, {0, 2, 2, 100}},
},
{
qfun: quantile{{0, 100}, {0.5, 100}, {1, 200}, {1, 300}},
rows: 4,
hist: testHistogram{{2, 0, 0, 100}, {1, 1, 1, 200}},
hist: testHistogram{{2, 0, 0, 100}, {0, 2, 2, 200}},
},
{
qfun: quantile{{0, 0}, {0.875, 87.5}, {1, 100}},
rows: 8,
hist: testHistogram{{0, 0, 0, 0}, {1, 6, 6, 87.5}, {0, 1, 1, 100}},
hist: testHistogram{{0, 0, 0, 0}, {0, 7, 7, 87.5}, {0, 1, 1, 100}},
},
{
qfun: quantile{{0, 400}, {0.5, 600}, {0.75, 700}, {1, 800}},
rows: 16,
hist: testHistogram{{0, 0, 0, 400}, {1, 7, 7, 600}, {1, 3, 3, 700}, {1, 3, 3, 800}},
hist: testHistogram{{0, 0, 0, 400}, {0, 8, 8, 600}, {0, 4, 4, 700}, {0, 4, 4, 800}},
},
// Error cases.
{
Expand Down