prometheus/storage/metric/operation.go

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// Copyright 2013 Prometheus Team
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package metric
import (
"fmt"
"github.com/prometheus/prometheus/model"
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"math"
"sort"
"time"
)
// Encapsulates a primitive query operation.
type op interface {
// The time at which this operation starts.
StartsAt() time.Time
// Extract samples from stream of values and advance operation time.
ExtractSamples(in model.Values) (out model.Values)
// Get current operation time or nil if no subsequent work associated with
// this operator remains.
CurrentTime() *time.Time
// GreedierThan indicates whether this present operation should take
// precedence over the other operation due to greediness.
//
// A critical assumption is that this operator and the other occur at the
// same time: this.StartsAt().Equal(op.StartsAt()).
GreedierThan(op) bool
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}
// Provides a sortable collection of operations.
type ops []op
func (o ops) Len() int {
return len(o)
}
// startsAtSort implements the sorting protocol and allows operator to be sorted
// in chronological order by when they start.
type startsAtSort struct {
ops
}
func (s startsAtSort) Less(i, j int) bool {
return s.ops[i].StartsAt().Before(s.ops[j].StartsAt())
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}
func (o ops) Swap(i, j int) {
o[i], o[j] = o[j], o[i]
}
// Encapsulates getting values at or adjacent to a specific time.
type getValuesAtTimeOp struct {
time time.Time
consumed bool
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}
func (o getValuesAtTimeOp) String() string {
return fmt.Sprintf("getValuesAtTimeOp at %s", o.time)
}
func (g getValuesAtTimeOp) StartsAt() time.Time {
return g.time
}
func (g *getValuesAtTimeOp) ExtractSamples(in model.Values) (out model.Values) {
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if len(in) == 0 {
return
}
out = extractValuesAroundTime(g.time, in)
g.consumed = true
return
}
func (g getValuesAtTimeOp) GreedierThan(op op) (superior bool) {
switch op.(type) {
case *getValuesAtTimeOp:
superior = true
case durationOperator:
superior = false
default:
panic("unknown operation")
}
return
}
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// extractValuesAroundTime searches for the provided time in the list of
// available samples and emits a slice containing the data points that
// are adjacent to it.
//
// An assumption of this is that the provided samples are already sorted!
func extractValuesAroundTime(t time.Time, in model.Values) (out model.Values) {
i := sort.Search(len(in), func(i int) bool {
return !in[i].Timestamp.Before(t)
})
if i == len(in) {
// Target time is past the end, return only the last sample.
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out = in[len(in)-1:]
} else {
if in[i].Timestamp.Equal(t) && len(in) > i+1 {
// We hit exactly the current sample time. Very unlikely in practice.
// Return only the current sample.
out = append(out, in[i])
} else {
if i == 0 {
// We hit before the first sample time. Return only the first sample.
out = append(out, in[0:1]...)
} else {
// We hit between two samples. Return both surrounding samples.
out = append(out, in[i-1:i+1]...)
}
}
}
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return
}
func (g getValuesAtTimeOp) CurrentTime() (currentTime *time.Time) {
if !g.consumed {
currentTime = &g.time
}
return
}
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// Encapsulates getting values at a given interval over a duration.
type getValuesAtIntervalOp struct {
from time.Time
through time.Time
interval time.Duration
}
func (o getValuesAtIntervalOp) String() string {
return fmt.Sprintf("getValuesAtIntervalOp from %s each %s through %s", o.from, o.interval, o.through)
}
func (g getValuesAtIntervalOp) StartsAt() time.Time {
return g.from
}
func (g getValuesAtIntervalOp) Through() time.Time {
return g.through
}
func (g *getValuesAtIntervalOp) ExtractSamples(in model.Values) (out model.Values) {
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if len(in) == 0 {
return
}
lastChunkTime := in[len(in)-1].Timestamp
for {
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out = extractValuesAroundTime(g.from, in)
g.from = g.from.Add(g.interval)
if g.from.After(lastChunkTime) {
break
}
if g.from.After(g.through) {
break
}
}
return
}
func (g getValuesAtIntervalOp) CurrentTime() (currentTime *time.Time) {
if g.from.After(g.through) {
return
}
return &g.from
}
func (g getValuesAtIntervalOp) GreedierThan(op op) (superior bool) {
switch o := op.(type) {
case *getValuesAtTimeOp:
superior = true
case durationOperator:
superior = g.Through().After(o.Through())
default:
panic("unknown operation")
}
return
}
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type getValuesAlongRangeOp struct {
from time.Time
through time.Time
}
func (o getValuesAlongRangeOp) String() string {
return fmt.Sprintf("getValuesAlongRangeOp from %s through %s", o.from, o.through)
}
func (g getValuesAlongRangeOp) StartsAt() time.Time {
return g.from
}
func (g getValuesAlongRangeOp) Through() time.Time {
return g.through
}
func (g *getValuesAlongRangeOp) ExtractSamples(in model.Values) (out model.Values) {
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if len(in) == 0 {
return
}
// Find the first sample where time >= g.from.
firstIdx := sort.Search(len(in), func(i int) bool {
return !in[i].Timestamp.Before(g.from)
})
if firstIdx == len(in) {
// No samples at or after operator start time. This can only happen if we
// try applying the operator to a time after the last recorded sample. In
// this case, we're finished.
g.from = g.through.Add(1)
return
}
// Find the first sample where time > g.through.
lastIdx := sort.Search(len(in), func(i int) bool {
return in[i].Timestamp.After(g.through)
})
if lastIdx == firstIdx {
g.from = g.through.Add(1)
return
}
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lastSampleTime := in[lastIdx-1].Timestamp
// Sample times are stored with a maximum time resolution of one second, so
// we have to add exactly that to target the next chunk on the next op
// iteration.
g.from = lastSampleTime.Add(time.Second)
return in[firstIdx:lastIdx]
}
func (g getValuesAlongRangeOp) CurrentTime() (currentTime *time.Time) {
if g.from.After(g.through) {
return
}
return &g.from
}
func (g getValuesAlongRangeOp) GreedierThan(op op) (superior bool) {
switch o := op.(type) {
case *getValuesAtTimeOp:
superior = true
case durationOperator:
superior = g.Through().After(o.Through())
default:
panic("unknown operation")
}
return
}
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// Provides a collection of getMetricRangeOperation.
type getMetricRangeOperations []*getValuesAlongRangeOp
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func (s getMetricRangeOperations) Len() int {
return len(s)
}
func (s getMetricRangeOperations) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
// Sorts getMetricRangeOperation according to duration in descending order.
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type rangeDurationSorter struct {
getMetricRangeOperations
}
func (s rangeDurationSorter) Less(i, j int) bool {
l := s.getMetricRangeOperations[i]
r := s.getMetricRangeOperations[j]
return !l.through.Before(r.through)
}
// Encapsulates a general operation that occurs over a duration.
type durationOperator interface {
op
Through() time.Time
}
// greedinessSort sorts the operations in descending order by level of
// greediness.
type greedinessSort struct {
ops
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}
func (g greedinessSort) Less(i, j int) bool {
return g.ops[i].GreedierThan(g.ops[j])
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}
// Contains getValuesAtIntervalOp operations.
type getValuesAtIntervalOps []*getValuesAtIntervalOp
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func (s getValuesAtIntervalOps) Len() int {
return len(s)
}
func (s getValuesAtIntervalOps) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
// Sorts durationOperator by the operation's duration in descending order.
type intervalDurationSorter struct {
getValuesAtIntervalOps
}
func (s intervalDurationSorter) Less(i, j int) bool {
l := s.getValuesAtIntervalOps[i]
r := s.getValuesAtIntervalOps[j]
return !l.through.Before(r.through)
}
// Sorts getValuesAtIntervalOp operations in ascending order by their
// frequency.
type frequencySorter struct {
getValuesAtIntervalOps
}
func (s frequencySorter) Less(i, j int) bool {
l := s.getValuesAtIntervalOps[i]
r := s.getValuesAtIntervalOps[j]
return l.interval < r.interval
}
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// Selects and returns all operations that are getValuesAtIntervalOp operations
// in a map whereby the operation interval is the key and the value are the
// operations sorted by respective level of greediness.
func collectIntervals(o ops) (intervals map[time.Duration]ops) {
intervals = make(map[time.Duration]ops)
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for _, operation := range o {
switch t := operation.(type) {
case *getValuesAtIntervalOp:
operations, _ := intervals[t.interval]
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operations = append(operations, t)
intervals[t.interval] = operations
}
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}
return
}
// Selects and returns all operations that are getValuesAlongRangeOp operations.
func collectRanges(ops ops) (ranges ops) {
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for _, operation := range ops {
switch t := operation.(type) {
case *getValuesAlongRangeOp:
ranges = append(ranges, t)
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}
}
return
}
// optimizeForward iteratively scans operations and peeks ahead to subsequent
// ones to find candidates that can either be removed or truncated through
// simplification. For instance, if a range query happens to overlap a get-a-
// value-at-a-certain-point-request, the range query should flatten and subsume
// the other.
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func optimizeForward(pending ops) (out ops) {
if len(pending) == 0 {
return
}
var (
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head op = pending[0]
tail ops
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)
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pending = pending[1:]
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switch t := head.(type) {
case *getValuesAtTimeOp:
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out = ops{head}
case *getValuesAtIntervalOp:
// If the last value was a scan at a given frequency along an interval,
// several optimizations may exist.
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for _, peekOperation := range pending {
if peekOperation.StartsAt().After(t.Through()) {
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break
}
// If the type is not a range request, we can't do anything.
switch next := peekOperation.(type) {
case *getValuesAlongRangeOp:
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if !next.GreedierThan(t) {
var (
before = getValuesAtIntervalOp(*t)
after = getValuesAtIntervalOp(*t)
)
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before.through = next.from
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// Truncate the get value at interval request if a range request cuts
// it off somewhere.
var (
from = next.from
)
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for !from.After(next.through) {
from = from.Add(t.interval)
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}
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after.from = from
pending = append(ops{&before, &after}, pending...)
sort.Sort(startsAtSort{pending})
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return optimizeForward(pending)
}
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}
}
case *getValuesAlongRangeOp:
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for _, peekOperation := range pending {
if peekOperation.StartsAt().After(t.Through()) {
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break
}
switch next := peekOperation.(type) {
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// All values at a specific time may be elided into the range query.
case *getValuesAtTimeOp:
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pending = pending[1:]
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continue
case *getValuesAlongRangeOp:
// Range queries should be concatenated if they overlap.
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if next.GreedierThan(t) {
next.from = t.from
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return optimizeForward(pending)
} else {
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pending = pending[1:]
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}
case *getValuesAtIntervalOp:
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pending = pending[1:]
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if next.GreedierThan(t) {
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var (
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nextStart = next.from
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)
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for !nextStart.After(next.through) {
nextStart = nextStart.Add(next.interval)
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}
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next.from = nextStart
tail = append(ops{next}, pending...)
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}
default:
panic("unknown operation type")
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}
}
default:
panic("unknown operation type")
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}
// Strictly needed?
sort.Sort(startsAtSort{pending})
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tail = optimizeForward(pending)
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return append(ops{head}, tail...)
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}
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// selectQueriesForTime chooses all subsequent operations from the slice that
// have the same start time as the provided time and emits them.
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func selectQueriesForTime(time time.Time, queries ops) (out ops) {
if len(queries) == 0 {
return
}
if !queries[0].StartsAt().Equal(time) {
return
}
out = append(out, queries[0])
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tail := selectQueriesForTime(time, queries[1:])
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return append(out, tail...)
}
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// selectGreediestRange scans through the various getValuesAlongRangeOp
// operations and emits the one that is the greediest.
func selectGreediestRange(in ops) (o durationOperator) {
if len(in) == 0 {
return
}
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sort.Sort(greedinessSort{in})
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o = in[0].(*getValuesAlongRangeOp)
return
}
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// selectGreediestIntervals scans through the various getValuesAtIntervalOp
// operations and emits a map of the greediest operation keyed by its start
// time.
func selectGreediestIntervals(in map[time.Duration]ops) (out map[time.Duration]durationOperator) {
if len(in) == 0 {
return
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}
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out = make(map[time.Duration]durationOperator)
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for i, ops := range in {
sort.Sort(greedinessSort{ops})
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out[i] = ops[0].(*getValuesAtIntervalOp)
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}
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return
}
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// rewriteForGreediestRange rewrites the current pending operation such that the
// greediest range operation takes precedence over all other operators in this
// time group.
//
// Between two range operations O1 and O2, they both start at the same time;
// however, O2 extends for a longer duration than O1. Thusly, O1 should be
// deleted with O2.
//
// O1------>|
// T1 T4
//
// O2------------>|
// T1 T7
//
// Thusly O1 can be squashed into O2 without having side-effects.
func rewriteForGreediestRange(greediestRange durationOperator) ops {
return ops{greediestRange}
}
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// rewriteForGreediestInterval rewrites teh current pending interval operations
// such that the interval operation with the smallest collection period is
// invoked first, for it will skip around the soonest of any of the remaining
// other operators.
//
// Between two interval operations O1 and O2, they both start at the same time;
// however, O2's period is shorter than O1, meaning it will sample far more
// frequently from the underlying time series. Thusly, O2 should start before
// O1.
//
// O1---->|---->|
// T1 T5
//
// O2->|->|->|->|
// T1 T5
//
// The rewriter presently does not scan and compact for common divisors in the
// periods, though this may be nice to have. For instance, if O1 has a period
// of 2 and O2 has a period of 4, O2 would be dropped for O1 would implicitly
// cover its period.
func rewriteForGreediestInterval(greediestIntervals map[time.Duration]durationOperator) ops {
var (
memo getValuesAtIntervalOps
out ops
)
for _, o := range greediestIntervals {
memo = append(memo, o.(*getValuesAtIntervalOp))
}
sort.Sort(frequencySorter{memo})
for _, o := range memo {
out = append(out, o)
}
return out
}
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// rewriteForRangeAndInterval examines the existence of a range operation and a
// set of interval operations that start at the same time and deletes all
// interval operations that start and finish before the range operation
// completes and rewrites all interval operations that continue longer than
// the range operation to start at the next best increment after the range.
//
// Assume that we have a range operator O1 and two interval operations O2 and
// O3. O2 and O3 have the same period (i.e., sampling interval), but O2
// terminates before O1 and O3 continue beyond O1.
//
// O1------------>|
// T1------------T7
//
// O2-->|-->|-->|
// T1----------T6
//
// O3-->|-->|-->|-->|-->|
// T1------------------T10
//
// This scenario will be rewritten such that O2 is deleted and O3 is truncated
// from T1 through T7, and O3's new starting time is at T7 and runs through T10:
//
// O1------------>|
// T1------------T7
//
// O2>|-->|
// T7---T10
//
// All rewritten interval operators will respect their original start time
// multipliers.
func rewriteForRangeAndInterval(greediestRange durationOperator, greediestIntervals map[time.Duration]durationOperator) (out ops) {
out = append(out, greediestRange)
for _, op := range greediestIntervals {
if !op.GreedierThan(greediestRange) {
continue
}
// The range operation does not exceed interval. Leave a snippet of
// interval.
var (
truncated = op.(*getValuesAtIntervalOp)
newIntervalOperation getValuesAtIntervalOp
// Refactor
remainingSlice = greediestRange.Through().Sub(greediestRange.StartsAt()) / time.Second
nextIntervalPoint = time.Duration(math.Ceil(float64(remainingSlice)/float64(truncated.interval)) * float64(truncated.interval/time.Second))
nextStart = greediestRange.Through().Add(nextIntervalPoint)
)
newIntervalOperation.from = nextStart
newIntervalOperation.interval = truncated.interval
newIntervalOperation.through = truncated.Through()
// Added back to the pending because additional curation could be
// necessary.
out = append(out, &newIntervalOperation)
}
return
}
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// Flattens queries that occur at the same time according to duration and level
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// of greed. Consult the various rewriter functions for their respective modes
// of operation.
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func optimizeTimeGroup(group ops) (out ops) {
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var (
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greediestRange = selectGreediestRange(collectRanges(group))
greediestIntervals = selectGreediestIntervals(collectIntervals(group))
containsRange = greediestRange != nil
containsInterval = len(greediestIntervals) > 0
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)
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switch {
case containsRange && !containsInterval:
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out = rewriteForGreediestRange(greediestRange)
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case !containsRange && containsInterval:
out = rewriteForGreediestInterval(greediestIntervals)
case containsRange && containsInterval:
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out = rewriteForRangeAndInterval(greediestRange, greediestIntervals)
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default:
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// Operation is OK as-is.
out = append(out, group[0])
}
return
}
// Flattens all groups of time according to greed.
func optimizeTimeGroups(pending ops) (out ops) {
if len(pending) == 0 {
return
}
sort.Sort(startsAtSort{pending})
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var (
nextOperation = pending[0]
groupedQueries = selectQueriesForTime(nextOperation.StartsAt(), pending)
)
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out = optimizeTimeGroup(groupedQueries)
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pending = pending[len(groupedQueries):]
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tail := optimizeTimeGroups(pending)
return append(out, tail...)
}
func optimize(pending ops) (out ops) {
return optimizeForward(optimizeTimeGroups(pending))
}