Safe Haskell	None
Language	GHC2021

Ecluse.Core.Server.Admission.Brake

Contents

The marks
One step
Reading the collector

Description

The memory budget's feedback: how one sample of the collector and the heap moves the budget.

After each major collection the brake measures the live data outside the charges, so the budget may grow until charges and that measured remainder reach the live ceiling. The ceiling also leaves room under the heap's overflow point for the largest request seen lately, which may run past the budget. The brake halves the budget when the collector takes too much of the CPU or the heap nears overflow, and grows it back in small steps while the collector stays calm. Ecluse.Rts.Sampler feeds it.

Synopsis

data BrakeMarks = BrakeMarks {
- bmGcHighPermille :: Int
- bmGcLowPermille :: Int
- bmKernelHighPermille :: Int
- bmOverflowGuardPermille :: Int
- bmCalmSamples :: Int
- bmGrowPermille :: Int
- bmReturnPermille :: Int
- bmForgetShift :: Int
- bmCooldownSamples :: Int
}
defaultBrakeMarks :: BrakeMarks
data BrakeState = BrakeState {
- bsBudget :: Int
- bsOutside :: Maybe Int
- bsLargestRequest :: Int
- bsCalmSamples :: Int
- bsCooldown :: Int
- bsLevel :: BrakeLevel
}
initialBrakeState :: BrakeBounds -> BrakeState
data GcSample = GcSample {
- gsGcSharePermille :: Maybe Int
- gsLiveAfterMajor :: Maybe Int
- gsChargedBytes :: Int
- gsLargestCharge :: Int
- gsKernelPermille :: Maybe Int
}
brakeStep :: BrakeMarks -> BrakeBounds -> BrakeState -> GcSample -> BrakeState
data CollectorReading = CollectorReading {
- crCpuNs :: Int64
- crGcCpuNs :: Int64
- crMajorCollections :: Word32
- crLiveBytes :: Int
}
gcSharePermille :: CollectorReading -> CollectorReading -> Maybe Int
data SampleWindow
newSampleWindow :: Int -> SampleWindow
windowSample :: SampleWindow -> Maybe CollectorReading -> Int -> Int -> Maybe Int -> (GcSample, SampleWindow)

The marks

data BrakeMarks Source #

The brake's thresholds. Shares are thousandths of the process's CPU time over the sampler's window.

Constructors

BrakeMarks

Fields

bmGcHighPermille :: Int
Above this GC share of CPU, the budget halves.
bmGcLowPermille :: Int
Below this GC share of CPU, the budget may grow.
bmKernelHighPermille :: Int
Above this share of the cgroup limit in use (less reclaimable file pages), the budget halves.
bmOverflowGuardPermille :: Int
Above this share of the copying collector's overflow point in live data, the budget halves.
bmCalmSamples :: Int
Consecutive calm samples before one growth step.
bmGrowPermille :: Int
One growth step, as a share of the current budget.
bmReturnPermille :: Int
How much of a fall in the measured outside live data one major collection gives back.
bmForgetShift :: Int
The largest request seen fades by one part in 2^shift per sample.
bmCooldownSamples :: Int
The fewest samples from one halving to the next.

Instances

Instances details

Show BrakeMarks Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods showsPrec :: Int -> BrakeMarks -> ShowS # show :: BrakeMarks -> String # showList :: [BrakeMarks] -> ShowS #
Eq BrakeMarks Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods (==) :: BrakeMarks -> BrakeMarks -> Bool # (/=) :: BrakeMarks -> BrakeMarks -> Bool #

defaultBrakeMarks :: BrakeMarks Source #

Above half the CPU the collector is thrashing, the point where Go's memory limit stops helping. A loaded proxy with no memory pressure spends 20 to 34% of its CPU in the collector.

One step

data BrakeState Source #

The brake's memory between samples.

Constructors

BrakeState
Fields bsBudget :: Int bsOutside :: Maybe Int Live data outside the charges at recent major collections. `Nothing` before the first. bsLargestRequest :: Int The largest charge one request reached lately, fading while no request matches it. bsCalmSamples :: Int bsCooldown :: Int Samples left before pressure may halve the budget again. bsLevel :: BrakeLevel

Instances

Instances details

Show BrakeState Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods showsPrec :: Int -> BrakeState -> ShowS # show :: BrakeState -> String # showList :: [BrakeState] -> ShowS #
Eq BrakeState Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods (==) :: BrakeState -> BrakeState -> Bool # (/=) :: BrakeState -> BrakeState -> Bool #

initialBrakeState :: BrakeBounds -> BrakeState Source #

Start at the boot budget, with nothing measured yet.

data GcSample Source #

One sample's readings. A missing reading leaves its rule out of this step.

Constructors

GcSample

Fields

gsGcSharePermille :: Maybe Int
The collector's share of CPU over the window. Nothing when the process was idle.
gsLiveAfterMajor :: Maybe Int
Live bytes, present only when a major collection finished since the last sample.
gsChargedBytes :: Int
What the meter held when the sample was taken.
gsLargestCharge :: Int
The largest total one request reached since the previous sample.
gsKernelPermille :: Maybe Int
The cgroup's non-reclaimable use against its limit, when a limit binds.

Instances

Instances details

Show GcSample Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods showsPrec :: Int -> GcSample -> ShowS # show :: GcSample -> String # showList :: [GcSample] -> ShowS #
Eq GcSample Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods (==) :: GcSample -> GcSample -> Bool # (/=) :: GcSample -> GcSample -> Bool #

brakeStep :: BrakeMarks -> BrakeBounds -> BrakeState -> GcSample -> BrakeState Source #

Move the budget by one sample: pressure halves it at most once per cooldown, a lower ceiling cuts it at once, and only a calm stretch grows it. It stays between the floor and the ceiling.

Reading the collector

data CollectorReading Source #

The collector's cumulative counters at one sample.

Constructors

CollectorReading
Fields crCpuNs :: Int64 Process CPU time, collector included. crGcCpuNs :: Int64 Collector CPU time. crMajorCollections :: Word32 crLiveBytes :: Int Live bytes after the latest collection, exact after a major one.

Instances

Instances details

Show CollectorReading Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods showsPrec :: Int -> CollectorReading -> ShowS # show :: CollectorReading -> String # showList :: [CollectorReading] -> ShowS #
Eq CollectorReading Source #
Instance details Defined in Ecluse.Core.Server.Admission.Brake Methods (==) :: CollectorReading -> CollectorReading -> Bool # (/=) :: CollectorReading -> CollectorReading -> Bool #

gcSharePermille :: CollectorReading -> CollectorReading -> Maybe Int Source #

The collector's share of the CPU between two readings, or Nothing when no CPU passed.

data SampleWindow Source #

The recent readings the GC share spans, newest first, and the capacity of that span.

newSampleWindow :: Int -> SampleWindow Source #

An empty window that spans the given number of sampling periods.

windowSample :: SampleWindow -> Maybe CollectorReading -> Int -> Int -> Maybe Int -> (GcSample, SampleWindow) Source #

Fold one reading into the window and form the brake's sample. Live data counts only after a major collection since an earlier reading, and a missing reading (no -T) leaves the collector's rules out.