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statistics: collect singleton sketches in row sampler #68499

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0xPoe wants to merge 4 commits into from
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statistics: collect singleton sketches in row sampler #68499

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7eebdb8
statistics: collect singleton sketches in row sampler
0xPoe May 4, 2026
49f2459
docs: add comments for two sample rates
0xPoe May 25, 2026
ef312c7
docs: add comments for Sketeches
0xPoe May 25, 2026
60e5514
statistics: keep per-region singleton sketches when merging
0xPoe May 25, 2026
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2 changes: 1 addition & 1 deletion pkg/statistics/BUILD.bazel
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Expand Up @@ -81,7 +81,7 @@ go_test(
data = glob(["testdata/**"]),
embed = [":statistics"],
flaky = True,
shard_count = 44,
shard_count = 45,
deps = [
"//pkg/config",
"//pkg/meta/model",
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2 changes: 2 additions & 0 deletions pkg/statistics/constants.go
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Expand Up @@ -20,4 +20,6 @@ const (
DefaultTopNValue = 100
// DefaultHistogramBuckets is the default number of histogram buckets
DefaultHistogramBuckets = 256
// NDVSampleSkipRate is the sample rate at which sampling is skipped, so NDV sketches are built from every row.
NDVSampleSkipRate = 1
Comment on lines +23 to +24
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@time-and-fate time-and-fate May 25, 2026

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Why don't we just call it DefaultNDVSampleRate?

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@time-and-fate time-and-fate May 25, 2026

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Suggested change
// NDVSampleSkipRate is the sample rate at which sampling is skipped, so NDV sketches are built from every row.
NDVSampleSkipRate = 1
// NDVSampleSkipRate is the sample rate at which sampling is skipped. The default value is 1, so NDV sketches are built from every row.
NDVSampleSkipRate = 1

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@0xPoe 0xPoe May 25, 2026

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See #68499 (comment)

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@0xPoe 0xPoe May 25, 2026

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DefaultNDVSampleRate would be used when we integrate it with the priority queue. Then its default value would be 0.05, I guess. This is the value we use to skip sampling by default.

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@0xPoe 0xPoe May 25, 2026

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Or otherwise, we would end up with two defaults:

DefaultNDVSampleRate for normal tables as 1.

DefaultNDVSampleRateForBigTable for big tables as 0.05??

)
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