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Job queue with the introduction of blocked evaluations #726
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672f877
Schedulers create blocked eval if there are failed allocations
dadgar 253fa75
Blocked Eval tracker
dadgar 6b64176
Rename counters
dadgar 1797f0e
Make computed node class a string and add versioning
dadgar e9c9361
Buffered unblock
dadgar 5956bee
dedup blocked evals by job id
dadgar a987dec
Leader reaps and cancels duplicate evals
dadgar cc2ee4f
Disable blocked eval tracker when leadership is lost
dadgar 3d8e7d0
Address comments
dadgar 65b8b52
Remove running, system scheduler, and fix tg overriding eligibility
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@@ -15,7 +15,7 @@ client { | |
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# Set ourselves as thing one | ||
meta { | ||
thing = "two" | ||
ssd = "true" | ||
} | ||
} | ||
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@@ -0,0 +1,309 @@ | ||
package nomad | ||
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import ( | ||
"sync" | ||
"time" | ||
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"github.com/armon/go-metrics" | ||
"github.com/hashicorp/nomad/nomad/structs" | ||
) | ||
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const ( | ||
// unblockBuffer is the buffer size for the unblock channel. The buffer | ||
// should be large to ensure that the FSM doesn't block when calling Unblock | ||
// as this would apply back-pressure on Raft. | ||
unblockBuffer = 8096 | ||
) | ||
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// BlockedEvals is used to track evaluations that shouldn't be queued until a | ||
// certain class of nodes becomes available. An evaluation is put into the | ||
// blocked state when it is run through the scheduler and produced failed | ||
// allocations. It is unblocked when the capacity of a node that could run the | ||
// failed allocation becomes available. | ||
type BlockedEvals struct { | ||
evalBroker *EvalBroker | ||
enabled bool | ||
stats *BlockedStats | ||
l sync.RWMutex | ||
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// captured is the set of evaluations that are captured by computed node | ||
// classes. | ||
captured map[string]*structs.Evaluation | ||
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// escaped is the set of evaluations that have escaped computed node | ||
// classes. | ||
escaped map[string]*structs.Evaluation | ||
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// unblockCh is used to buffer unblocking of evaluations. | ||
capacityChangeCh chan string | ||
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// jobs is the map of blocked job and is used to ensure that only one | ||
// blocked eval exists for each job. | ||
jobs map[string]struct{} | ||
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// duplicates is the set of evaluations for jobs that had pre-existing | ||
// blocked evaluations. These should be marked as cancelled since only one | ||
// blocked eval is neeeded bper job. | ||
duplicates []*structs.Evaluation | ||
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// duplicateCh is used to signal that a duplicate eval was added to the | ||
// duplicate set. It can be used to unblock waiting callers looking for | ||
// duplicates. | ||
duplicateCh chan struct{} | ||
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// stopCh is used to stop any created goroutines. | ||
stopCh chan struct{} | ||
} | ||
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// BlockedStats returns all the stats about the blocked eval tracker. | ||
type BlockedStats struct { | ||
// TotalEscaped is the total number of blocked evaluations that have escaped | ||
// computed node classes. | ||
TotalEscaped int | ||
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// TotalBlocked is the total number of blocked evaluations. | ||
TotalBlocked int | ||
} | ||
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// NewBlockedEvals creates a new blocked eval tracker that will enqueue | ||
// unblocked evals into the passed broker. | ||
func NewBlockedEvals(evalBroker *EvalBroker) *BlockedEvals { | ||
return &BlockedEvals{ | ||
evalBroker: evalBroker, | ||
captured: make(map[string]*structs.Evaluation), | ||
escaped: make(map[string]*structs.Evaluation), | ||
jobs: make(map[string]struct{}), | ||
capacityChangeCh: make(chan string, unblockBuffer), | ||
duplicateCh: make(chan struct{}, 1), | ||
stopCh: make(chan struct{}), | ||
stats: new(BlockedStats), | ||
} | ||
} | ||
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// Enabled is used to check if the broker is enabled. | ||
func (b *BlockedEvals) Enabled() bool { | ||
b.l.RLock() | ||
defer b.l.RUnlock() | ||
return b.enabled | ||
} | ||
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// SetEnabled is used to control if the broker is enabled. The broker | ||
// should only be enabled on the active leader. | ||
func (b *BlockedEvals) SetEnabled(enabled bool) { | ||
b.l.Lock() | ||
if b.enabled == enabled { | ||
// No-op | ||
return | ||
} else if enabled { | ||
go b.watchCapacity() | ||
} else { | ||
close(b.stopCh) | ||
} | ||
b.enabled = enabled | ||
b.l.Unlock() | ||
if !enabled { | ||
b.Flush() | ||
} | ||
} | ||
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// Block tracks the passed evaluation and enqueues it into the eval broker when | ||
// a suitable node calls unblock. | ||
func (b *BlockedEvals) Block(eval *structs.Evaluation) { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Do nothing if not enabled | ||
if !b.enabled { | ||
return | ||
} | ||
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// Check if the job already has a blocked evaluation. If it does add it to | ||
// the list of duplicates. We omly ever want one blocked evaluation per job, | ||
// otherwise we would create unnecessary work for the scheduler as multiple | ||
// evals for the same job would be run, all producing the same outcome. | ||
if _, existing := b.jobs[eval.JobID]; existing { | ||
b.duplicates = append(b.duplicates, eval) | ||
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// Unblock any waiter. | ||
select { | ||
case b.duplicateCh <- struct{}{}: | ||
default: | ||
} | ||
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return | ||
} | ||
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// Mark the job as tracked. | ||
b.stats.TotalBlocked++ | ||
b.jobs[eval.JobID] = struct{}{} | ||
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// If the eval has escaped, meaning computed node classes could not capture | ||
// the constraints of the job, we store the eval separately as we have to | ||
// unblock it whenever node capacity changes. This is because we don't know | ||
// what node class is feasible for the jobs constraints. | ||
if eval.EscapedComputedClass { | ||
b.escaped[eval.ID] = eval | ||
b.stats.TotalEscaped++ | ||
return | ||
} | ||
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// Add the eval to the set of blocked evals whose jobs constraints are | ||
// captured by computed node class. | ||
b.captured[eval.ID] = eval | ||
} | ||
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// Unblock causes any evaluation that could potentially make progress on a | ||
// capacity change on the passed computed node class to be enqueued into the | ||
// eval broker. | ||
func (b *BlockedEvals) Unblock(computedClass string) { | ||
// Do nothing if not enabled | ||
if !b.enabled { | ||
return | ||
} | ||
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b.capacityChangeCh <- computedClass | ||
} | ||
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// watchCapacity is a long lived function that watches for capacity changes in | ||
// nodes and unblocks the correct set of evals. | ||
func (b *BlockedEvals) watchCapacity() { | ||
for { | ||
select { | ||
case <-b.stopCh: | ||
return | ||
case computedClass := <-b.capacityChangeCh: | ||
b.unblock(computedClass) | ||
} | ||
} | ||
} | ||
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// unblock unblocks all blocked evals that could run on the passed computed node | ||
// class. | ||
func (b *BlockedEvals) unblock(computedClass string) { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Protect against the case of a flush. | ||
if !b.enabled { | ||
return | ||
} | ||
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// Every eval that has escaped computed node class has to be unblocked | ||
// because any node could potentially be feasible. | ||
var unblocked []*structs.Evaluation | ||
if l := len(b.escaped); l != 0 { | ||
unblocked = make([]*structs.Evaluation, 0, l) | ||
for id, eval := range b.escaped { | ||
unblocked = append(unblocked, eval) | ||
delete(b.escaped, id) | ||
delete(b.jobs, eval.JobID) | ||
} | ||
} | ||
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// We unblock any eval that is explicitely eligible for the computed class | ||
// and also any eval that is not eligible or uneligible. This signifies that | ||
// when the evaluation was originally run through the scheduler, that it | ||
// never saw a node with the given computed class and thus needs to be | ||
// unblocked for correctness. | ||
for id, eval := range b.captured { | ||
if elig, ok := eval.ClassEligibility[computedClass]; ok && !elig { | ||
// Can skip because the eval has explicitely marked the node class | ||
// as ineligible. | ||
continue | ||
} | ||
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// The computed node class has never been seen by the eval so we unblock | ||
// it. | ||
unblocked = append(unblocked, eval) | ||
delete(b.jobs, eval.JobID) | ||
delete(b.captured, id) | ||
} | ||
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if l := len(unblocked); l != 0 { | ||
// Update the counters | ||
b.stats.TotalEscaped = 0 | ||
b.stats.TotalBlocked -= l | ||
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// Enqueue all the unblocked evals into the broker. | ||
b.evalBroker.EnqueueAll(unblocked) | ||
} | ||
} | ||
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// GetDuplicates returns all the duplicate evaluations and blocks until the | ||
// passed timeout. | ||
func (b *BlockedEvals) GetDuplicates(timeout time.Duration) []*structs.Evaluation { | ||
var timeoutTimer *time.Timer | ||
var timeoutCh <-chan time.Time | ||
SCAN: | ||
b.l.Lock() | ||
if len(b.duplicates) != 0 { | ||
dups := b.duplicates | ||
b.duplicates = nil | ||
b.l.Unlock() | ||
return dups | ||
} | ||
b.l.Unlock() | ||
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// Create the timer | ||
if timeoutTimer == nil && timeout != 0 { | ||
timeoutTimer = time.NewTimer(timeout) | ||
timeoutCh = timeoutTimer.C | ||
defer timeoutTimer.Stop() | ||
} | ||
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select { | ||
case <-b.stopCh: | ||
return nil | ||
case <-timeoutCh: | ||
return nil | ||
case <-b.duplicateCh: | ||
goto SCAN | ||
} | ||
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return nil | ||
} | ||
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// Flush is used to clear the state of blocked evaluations. | ||
func (b *BlockedEvals) Flush() { | ||
b.l.Lock() | ||
defer b.l.Unlock() | ||
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// Reset the blocked eval tracker. | ||
b.stats.TotalEscaped = 0 | ||
b.stats.TotalBlocked = 0 | ||
b.captured = make(map[string]*structs.Evaluation) | ||
b.escaped = make(map[string]*structs.Evaluation) | ||
b.jobs = make(map[string]struct{}) | ||
b.duplicates = nil | ||
b.capacityChangeCh = make(chan string, unblockBuffer) | ||
b.stopCh = make(chan struct{}) | ||
b.duplicateCh = make(chan struct{}, 1) | ||
} | ||
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// Stats is used to query the state of the blocked eval tracker. | ||
func (b *BlockedEvals) Stats() *BlockedStats { | ||
// Allocate a new stats struct | ||
stats := new(BlockedStats) | ||
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b.l.RLock() | ||
defer b.l.RUnlock() | ||
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// Copy all the stats | ||
stats.TotalEscaped = b.stats.TotalEscaped | ||
stats.TotalBlocked = b.stats.TotalBlocked | ||
return stats | ||
} | ||
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// EmitStats is used to export metrics about the blocked eval tracker while enabled | ||
func (b *BlockedEvals) EmitStats(period time.Duration, stopCh chan struct{}) { | ||
for { | ||
select { | ||
case <-time.After(period): | ||
stats := b.Stats() | ||
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_blocked"}, float32(stats.TotalBlocked)) | ||
metrics.SetGauge([]string{"nomad", "blocked_evals", "total_escaped"}, float32(stats.TotalEscaped)) | ||
case <-stopCh: | ||
return | ||
} | ||
} | ||
} |
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Doesn't seem to be called? Also we can probably use the internal stopCh
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Good catch, forgot to add the call. You want it to be the servers shutdown channel because otherwise you'll stop emitting stats when your not the leader and it won't start again even if you become a leader again.