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stats: refine updating stats using feedback #6796

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merged 6 commits into from
Jul 3, 2018
Merged

stats: refine updating stats using feedback #6796

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4d50383
stats: refine updating stats using feedback
Jun 8, 2018
ffb767d
Merge branch 'master' of github.com:pingcap/tidb into split
Jun 29, 2018
5aa6d4e
address comment
Jun 29, 2018
db52d40
address comment
Jul 3, 2018
2d77a9f
Merge branch 'master' into split
zz-jason Jul 3, 2018
3f7cab9
Merge branch 'master' into split
alivxxx Jul 3, 2018
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141 changes: 77 additions & 64 deletions statistics/feedback.go
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Original file line number Diff line number Diff line change
Expand Up @@ -174,7 +174,6 @@ type BucketFeedback struct {
feedback []feedback // All the feedback info in the same bucket.
lower *types.Datum // The lower bound of the new bucket.
upper *types.Datum // The upper bound of the new bucket.
scalar scalar // The scalar info for the boundary.
}

// buildBucketFeedback build the feedback for each bucket from the histogram feedback.
Expand Down Expand Up @@ -264,63 +263,24 @@ func (b *BucketFeedback) getBoundaries(num int) []types.Datum {

type bucket = feedback

// Get the fraction of the [lowerVal, upperVal] that intersect with the bucket boundary.
func (b *BucketFeedback) getFraction(lowerVal, upperVal *types.Datum) float64 {
var lower, upper float64
if b.lower.Kind() == types.KindBytes {
value := lowerVal.GetBytes()
lower = convertBytesToScalar(value[b.scalar.commonPfxLen:])
value = upperVal.GetBytes()
upper = convertBytesToScalar(value[b.scalar.commonPfxLen:])
} else {
lower = float64(lowerVal.GetInt64())
upper = float64(upperVal.GetInt64())
}
return calcFraction(b.scalar.lower, b.scalar.upper, upper) - calcFraction(b.scalar.lower, b.scalar.upper, lower)
}

func (b *BucketFeedback) getBucketCount(count float64) int64 {
// Get the scalar info for boundary.
prefixLen := commonPrefixLength(b.lower.GetBytes(), b.upper.GetBytes())
if b.lower.Kind() == types.KindBytes {
b.scalar.commonPfxLen = commonPrefixLength(b.lower.GetBytes(), b.upper.GetBytes())
b.scalar.lower = convertBytesToScalar(b.lower.GetBytes()[prefixLen:])
b.scalar.upper = convertBytesToScalar(b.upper.GetBytes()[prefixLen:])
} else {
b.scalar.lower = float64(b.lower.GetInt64())
b.scalar.upper = float64(b.upper.GetInt64())
}
// Use the feedback that covers most to update this bucket's count. We only consider feedback that covers at
// least minBucketFraction.
maxFraction := minBucketFraction
for _, fb := range b.feedback {
fraction := b.getFraction(fb.lower, fb.upper)
if fraction >= maxFraction {
maxFraction = fraction
count = float64(fb.count) / fraction
}
}
return int64(count)
}

// updateBucket split the bucket according to feedback.
func (b *BucketFeedback) splitBucket(newBktNum int, totalCount float64, count float64) []bucket {
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comment and method name not match.

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The count should be renamed to originBucketCount?

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s/newBktNum/newNumBkts

// do not split if the count is already too small.
if newBktNum <= 1 || count < minBucketFraction*totalCount {
bkt := bucket{lower: b.lower, upper: b.upper, count: int64(count)}
return []bucket{bkt}
}
// Split the bucket.
bounds := b.getBoundaries(newBktNum)
bounds := b.getBoundaries(newBktNum + 1)
bkts := make([]bucket, 0, len(bounds)-1)
for i := 1; i < len(bounds); i++ {
newCount := int64(count * b.getFraction(&bounds[i-1], &bounds[i]))
bkt := bucket{&bounds[i-1], bounds[i].Copy(), 0, 0}
// get bucket count
_, ratio := getOverlapFraction(feedback{b.lower, b.upper, int64(count), 0}, bkt)
bucketCount := count * ratio
bucketCount = b.bucketCount(bkt, bucketCount)
// do not split if the count of result bucket is too small.
if float64(newCount) < minBucketFraction*totalCount {
if bucketCount < minBucketFraction*totalCount {
bounds[i] = bounds[i-1]
continue
}
bkts = append(bkts, bucket{lower: &bounds[i-1], upper: bounds[i].Copy(), count: newCount, repeat: 0})
bkt.count = int64(bucketCount)
bkts = append(bkts, bkt)
// To guarantee that each bucket's range will not overlap.
if bounds[i].Kind() == types.KindBytes {
bounds[i].SetBytes(kv.Key(bounds[i].GetBytes()).PrefixNext())
Expand All @@ -333,6 +293,68 @@ func (b *BucketFeedback) splitBucket(newBktNum int, totalCount float64, count fl
return bkts
}

func getFraction4PK(minValue, maxValue, lower, upper *types.Datum) (float64, float64) {
if minValue.Kind() == types.KindInt64 {
l, r := float64(minValue.GetInt64()), float64(maxValue.GetInt64())
return calcFraction(l, r, float64(lower.GetInt64())), calcFraction(l, r, float64(upper.GetInt64()))
}
l, r := float64(minValue.GetUint64()), float64(maxValue.GetUint64())
return calcFraction(l, r, float64(lower.GetUint64())), calcFraction(l, r, float64(upper.GetUint64()))
}

func getFraction4Index(minValue, maxValue, lower, upper *types.Datum, prefixLen int) (float64, float64) {
l, r := convertBytesToScalar(minValue.GetBytes()[prefixLen:]), convertBytesToScalar(maxValue.GetBytes()[prefixLen:])
return calcFraction(l, r, convertBytesToScalar(lower.GetBytes()[prefixLen:])),
calcFraction(l, r, convertBytesToScalar(upper.GetBytes()[prefixLen:]))
}

// getOverlapFraction gets the overlap fraction of feedback and bucket range. In order to get the bucket count, it also
// returns the ratio between feedback fraction and bucket fraction.
func getOverlapFraction(fb feedback, bkt bucket) (float64, float64) {
datums := make([]types.Datum, 0, 4)
datums = append(datums, *fb.lower, *fb.upper)
datums = append(datums, *bkt.lower, *bkt.upper)
err := types.SortDatums(nil, datums)
if err != nil {
return 0, 0
}
var fbLower, fbUpper, bktLower, bktUpper float64
minValue, maxValue := &datums[0], &datums[3]
if datums[0].Kind() == types.KindBytes {
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What about add comment at the declaration of bucket to tell that the datum in bucket can only be Bytes or Int, and Bytes is for index and Int is for int pk.

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Done.

prefixLen := commonPrefixLength(minValue.GetBytes(), maxValue.GetBytes())
fbLower, fbUpper = getFraction4Index(minValue, maxValue, fb.lower, fb.upper, prefixLen)
bktLower, bktUpper = getFraction4Index(minValue, maxValue, bkt.lower, bkt.upper, prefixLen)
} else {
fbLower, fbUpper = getFraction4PK(minValue, maxValue, fb.lower, fb.upper)
bktLower, bktUpper = getFraction4PK(minValue, maxValue, bkt.lower, bkt.upper)
}
ratio := (bktUpper - bktLower) / (fbUpper - fbLower)
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The ratio seems not consistent with the comment, should be (fbUpper - fbLower) /(bktUpper - bktLower)?

And later we calculate the new bucket count with count * ratio.

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Yes, the comment is wrong. The count is the feedback count, so this ratio is right.

// full overlap
if fbLower <= bktLower && bktUpper <= fbUpper {
return bktUpper - bktLower, ratio
}
if bktLower <= fbLower && fbUpper <= bktUpper {
return fbUpper - fbLower, ratio
}
// partial overlap
overlap := math.Min(bktUpper-fbLower, fbUpper-bktLower)
return overlap, ratio
}

func (b *BucketFeedback) bucketCount(bkt bucket, defaultCount float64) float64 {
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How about name it refineBucketCount?
And add some comment about this method.

bestFraction := minBucketFraction
count := defaultCount
for _, fb := range b.feedback {
fraction, ratio := getOverlapFraction(fb, bkt)
// choose the max overlap fraction
if fraction > bestFraction {
bestFraction = fraction
count = float64(fb.count) * ratio
}
}
return count
}

// Get the split count for the histogram.
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Need to explain why choose this algorithm.

func getSplitCount(count, remainBuckets int) int {
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How about numFeedbacks instead of count?

remainBuckets = mathutil.Max(remainBuckets, 10)
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better use another variable like splitCount rather than modify the input argument.

Expand Down Expand Up @@ -425,31 +447,18 @@ func mergeBuckets(bkts []bucket, isNewBuckets []bool, totalCount float64) []buck

func splitBuckets(h *Histogram, feedback *QueryFeedback) ([]bucket, []bool, int64) {
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add comments about this function.

bktID2FB, fbNum := buildBucketFeedback(h, feedback)
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s/fbNum/totalNumFBs

counts := make([]int64, 0, h.Len())
for i := 0; i < h.Len(); i++ {
bkt, ok := bktID2FB[i]
if !ok {
counts = append(counts, h.bucketCount(i))
} else {
counts = append(counts, bkt.getBucketCount(float64(h.bucketCount(i))))
}
}
totCount := int64(0)
for _, count := range counts {
totCount += count
}
buckets := make([]bucket, 0, h.Len())
isNewBuckets := make([]bool, 0, h.Len())
splitCount := getSplitCount(fbNum, defaultBucketCount-h.Len())
for i := 0; i < h.Len(); i++ {
bkt, ok := bktID2FB[i]
// No feedback, just use the original one.
if !ok {
buckets = append(buckets, bucket{h.GetLower(i), h.GetUpper(i), counts[i], h.Buckets[i].Repeat})
buckets = append(buckets, bucket{h.GetLower(i), h.GetUpper(i), h.bucketCount(i), h.Buckets[i].Repeat})
isNewBuckets = append(isNewBuckets, false)
continue
}
bkts := bkt.splitBucket(splitCount*len(bkt.feedback)/fbNum, float64(totCount), float64(counts[i]))
bkts := bkt.splitBucket(splitCount*len(bkt.feedback)/fbNum, h.totalRowCount(), float64(h.bucketCount(i)))
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Need a dedicated variable for splitCount*len(bkt.feedback)/fbNum and add a comment to explain why.

buckets = append(buckets, bkts...)
if len(bkts) == 1 {
isNewBuckets = append(isNewBuckets, false)
Expand All @@ -459,6 +468,10 @@ func splitBuckets(h *Histogram, feedback *QueryFeedback) ([]bucket, []bool, int6
}
}
}
totCount := int64(0)
for _, bkt := range buckets {
totCount += bkt.count
}
return buckets, isNewBuckets, totCount
}

Expand Down
51 changes: 36 additions & 15 deletions statistics/feedback_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -67,15 +67,17 @@ func (s *testFeedbackSuite) TestUpdateHistogram(c *C) {
q := NewQueryFeedback(0, genHistogram(), 0, false)
q.feedback = feedbacks
originBucketCount := defaultBucketCount
defaultBucketCount = 5
defaultBucketCount = 7
defer func() { defaultBucketCount = originBucketCount }()
c.Assert(UpdateHistogram(q.Hist(), q).ToString(0), Equals,
"column:0 ndv:0 totColSize:0\n"+
"num: 10000\tlower_bound: 0\tupper_bound: 1\trepeats: 0\n"+
"num: 10003\tlower_bound: 2\tupper_bound: 3\trepeats: 0\n"+
"num: 10021\tlower_bound: 4\tupper_bound: 20\trepeats: 0\n"+
"num: 10046\tlower_bound: 21\tupper_bound: 46\trepeats: 0\n"+
"num: 10059\tlower_bound: 47\tupper_bound: 60\trepeats: 0")
"num: 10008\tlower_bound: 2\tupper_bound: 7\trepeats: 0\n"+
"num: 10019\tlower_bound: 8\tupper_bound: 19\trepeats: 0\n"+
"num: 10019\tlower_bound: 20\tupper_bound: 20\trepeats: 0\n"+
"num: 10037\tlower_bound: 21\tupper_bound: 39\trepeats: 0\n"+
"num: 10055\tlower_bound: 40\tupper_bound: 58\trepeats: 0\n"+
"num: 10057\tlower_bound: 59\tupper_bound: 60\trepeats: 0")
}

func (s *testFeedbackSuite) TestSplitBuckets(c *C) {
Expand All @@ -93,10 +95,10 @@ func (s *testFeedbackSuite) TestSplitBuckets(c *C) {
"num: 1\tlower_bound: 2\tupper_bound: 3\trepeats: 0\n"+
"num: 1\tlower_bound: 5\tupper_bound: 7\trepeats: 0\n"+
"num: 6\tlower_bound: 10\tupper_bound: 15\trepeats: 0\n"+
"num: 10\tlower_bound: 16\tupper_bound: 20\trepeats: 0\n"+
"num: 10\tlower_bound: 30\tupper_bound: 50\trepeats: 0")
"num: 6\tlower_bound: 16\tupper_bound: 20\trepeats: 0\n"+
"num: 6\tlower_bound: 30\tupper_bound: 50\trepeats: 0")
c.Assert(isNewBuckets, DeepEquals, []bool{false, false, false, true, true, false})
c.Assert(totalCount, Equals, int64(11))
c.Assert(totalCount, Equals, int64(6))

// test do not split if the bucket count is too small
feedbacks = []feedback{newFeedback(0, 1, 100000)}
Expand All @@ -111,26 +113,45 @@ func (s *testFeedbackSuite) TestSplitBuckets(c *C) {
"num: 100000\tlower_bound: 0\tupper_bound: 1\trepeats: 0\n"+
"num: 100000\tlower_bound: 2\tupper_bound: 3\trepeats: 0\n"+
"num: 100000\tlower_bound: 5\tupper_bound: 7\trepeats: 0\n"+
"num: 100002\tlower_bound: 10\tupper_bound: 20\trepeats: 0\n"+
"num: 100002\tlower_bound: 30\tupper_bound: 50\trepeats: 0")
c.Assert(isNewBuckets, DeepEquals, []bool{false, false, false, false, false})
c.Assert(totalCount, Equals, int64(100002))
"num: 100001\tlower_bound: 10\tupper_bound: 15\trepeats: 0\n"+
"num: 100001\tlower_bound: 16\tupper_bound: 20\trepeats: 0\n"+
"num: 100001\tlower_bound: 30\tupper_bound: 50\trepeats: 0")
c.Assert(isNewBuckets, DeepEquals, []bool{false, false, false, true, true, false})
c.Assert(totalCount, Equals, int64(100001))

// test do not split if the result bucket count is too small
h := NewHistogram(0, 0, 0, 0, types.NewFieldType(mysql.TypeLong), 5, 0)
appendBucket(h, 0, 1000000)
h.Buckets[0].Count = 1000000
feedbacks = feedbacks[:0]
for i := 0; i < 100; i++ {
feedbacks = append(feedbacks, newFeedback(0, 101, 1))
feedbacks = append(feedbacks, newFeedback(0, 10, 1))
}
q = NewQueryFeedback(0, h, 0, false)
q.feedback = feedbacks
buckets, isNewBuckets, totalCount = splitBuckets(q.Hist(), q)
c.Assert(buildNewHistogram(q.Hist(), buckets).ToString(0), Equals,
"column:0 ndv:0 totColSize:0\n"+
"num: 9900\tlower_bound: 0\tupper_bound: 1000000\trepeats: 0")
"num: 1000000\tlower_bound: 0\tupper_bound: 1000000\trepeats: 0")
c.Assert(isNewBuckets, DeepEquals, []bool{false})
c.Assert(totalCount, Equals, int64(9900))
c.Assert(totalCount, Equals, int64(1000000))

// test split even if the feedback range is too small
h = NewHistogram(0, 0, 0, 0, types.NewFieldType(mysql.TypeLong), 5, 0)
appendBucket(h, 0, 1000000)
feedbacks = feedbacks[:0]
for i := 0; i < 100; i++ {
feedbacks = append(feedbacks, newFeedback(0, 10, 1))
}
q = NewQueryFeedback(0, h, 0, false)
q.feedback = feedbacks
buckets, isNewBuckets, totalCount = splitBuckets(q.Hist(), q)
c.Assert(buildNewHistogram(q.Hist(), buckets).ToString(0), Equals,
"column:0 ndv:0 totColSize:0\n"+
"num: 1\tlower_bound: 0\tupper_bound: 10\trepeats: 0\n"+
"num: 1\tlower_bound: 11\tupper_bound: 1000000\trepeats: 0")
c.Assert(isNewBuckets, DeepEquals, []bool{true, true})
c.Assert(totalCount, Equals, int64(1))
}

func (s *testFeedbackSuite) TestMergeBuckets(c *C) {
Expand Down