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release-22.2: kvserver: lower score threshold for mvcc GC eligibility #92675

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Dec 1, 2022
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release-22.2: kvserver: lower score threshold for mvcc GC eligibility #92675

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39 changes: 35 additions & 4 deletions pkg/kv/kvserver/mvcc_gc_queue.go
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ import (
"github.com/cockroachdb/cockroach/pkg/settings/cluster"
"github.com/cockroachdb/cockroach/pkg/spanconfig"
"github.com/cockroachdb/cockroach/pkg/storage/enginepb"
"github.com/cockroachdb/cockroach/pkg/util"
"github.com/cockroachdb/cockroach/pkg/util/admission/admissionpb"
"github.com/cockroachdb/cockroach/pkg/util/contextutil"
"github.com/cockroachdb/cockroach/pkg/util/hlc"
Expand All @@ -53,6 +54,11 @@ const (
// for ranged intent resolution if it exceeds the timeout.
mvccGCQueueIntentBatchTimeout = 2 * time.Minute

// mvccGCQueueCooldownDuration is duration to wait between MVCC GC attempts of
// the same rage when triggered by a low score threshold. This cooldown time
// is reduced proportionally to score and becomes 0 when score reaches a
// mvccGCKeyScoreNoCooldownThreshold score.
mvccGCQueueCooldownDuration = 2 * time.Hour
// mvccGCQueueIntentCooldownDuration is the duration to wait between MVCC GC
// attempts of the same range when triggered solely by intents. This is to
// prevent continually spinning on intents that belong to active transactions,
Expand All @@ -64,9 +70,10 @@ const (

// Thresholds used to decide whether to queue for MVCC GC based on keys and
// intents.
mvccGCKeyScoreThreshold = 2
mvccGCIntentScoreThreshold = 1
mvccGCDropRangeKeyScoreThreshold = 1
mvccGCKeyScoreThreshold = 1
mvccGCKeyScoreNoCooldownThreshold = 2
mvccGCIntentScoreThreshold = 1
mvccGCDropRangeKeyScoreThreshold = 1

probablyLargeAbortSpanSysCountThreshold = 10000
largeAbortSpanBytesThreshold = 16 * (1 << 20) // 16mb
Expand Down Expand Up @@ -447,8 +454,32 @@ func makeMVCCGCQueueScoreImpl(
valScore := r.DeadFraction * r.ValuesScalableScore
r.FinalScore = r.FuzzFactor * (valScore + r.IntentScore)

// Check GC queueing eligibility using cooldown discounted by score.
isGCScoreMet := func(score float64, minThreshold, maxThreshold float64, cooldown time.Duration) bool {
if minThreshold > maxThreshold {
if util.RaceEnabled {
log.Fatalf(ctx,
"invalid cooldown score thresholds. min (%f) must be less or equal to max (%f)",
minThreshold, maxThreshold)
}
// Swap thresholds for non test builds. This should never happen in practice.
minThreshold, maxThreshold = maxThreshold, minThreshold
}
// Cool down rate is how much we want to cool down after previous gc based
// on the score. If score is at min threshold we would wait for cooldown
// time, it is proportionally reduced as score reaches maxThreshold and is
// zero at maxThreshold which means no cooldown is necessary.
coolDownRate := 1 - (score-minThreshold)/(maxThreshold-minThreshold)
adjustedCoolDown := time.Duration(int64(float64(cooldown.Nanoseconds()) * coolDownRate))
if score > minThreshold && (r.LastGC == 0 || r.LastGC >= adjustedCoolDown) {
return true
}
return false
}

// First determine whether we should queue based on MVCC score alone.
r.ShouldQueue = canAdvanceGCThreshold && r.FuzzFactor*valScore > mvccGCKeyScoreThreshold
r.ShouldQueue = canAdvanceGCThreshold && isGCScoreMet(r.FuzzFactor*valScore, mvccGCKeyScoreThreshold,
mvccGCKeyScoreNoCooldownThreshold, mvccGCQueueCooldownDuration)

// Next, determine whether we should queue based on intent score. For
// intents, we also enforce a cooldown time since we may not actually
Expand Down
66 changes: 43 additions & 23 deletions pkg/kv/kvserver/mvcc_gc_queue_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -354,12 +354,21 @@ func (cws *cachedWriteSimulator) singleKeySteady(
}

func (cws *cachedWriteSimulator) shouldQueue(
b bool, prio float64, after time.Duration, ttl time.Duration, ms enginepb.MVCCStats,
b bool,
prio float64,
after time.Duration,
ttl time.Duration,
ms enginepb.MVCCStats,
timeSinceGC time.Duration,
) {
cws.t.Helper()
ts := hlc.Timestamp{}.Add(ms.LastUpdateNanos+after.Nanoseconds(), 0)
prevGCTs := hlc.Timestamp{}
if timeSinceGC > 0 {
prevGCTs = prevGCTs.Add(ms.LastUpdateNanos+(after-timeSinceGC).Nanoseconds(), 0)
}
r := makeMVCCGCQueueScoreImpl(context.Background(), 0 /* seed */, ts, ms, ttl,
hlc.Timestamp{}, true, /* canAdvanceGCThreshold */
prevGCTs, true, /* canAdvanceGCThreshold */
roachpb.GCHint{}, time.Hour, /* txnCleanupThreshold */
)
if fmt.Sprintf("%.2f", r.FinalScore) != fmt.Sprintf("%.2f", prio) || b != r.ShouldQueue {
Expand All @@ -386,6 +395,7 @@ func TestMVCCGCQueueMakeGCScoreRealistic(t *testing.T) {
}

minuteTTL, hourTTL := time.Minute, time.Hour
const never = time.Duration(0)

{
// Hammer a key with 1MB blobs for a (simulated) minute. Logically, at
Expand All @@ -400,32 +410,39 @@ func TestMVCCGCQueueMakeGCScoreRealistic(t *testing.T) {
//
// Since at the time of this check the data is already 30s old on
// average (i.e. ~30x the TTL), we expect to *really* want GC.
cws.shouldQueue(true, 28.94, time.Duration(0), 0, ms)
cws.shouldQueue(true, 28.94, time.Duration(0), 0, ms)
cws.shouldQueue(true, 28.94, time.Duration(0), 0, ms, never)
cws.shouldQueue(true, 28.94, time.Duration(0), 0, ms, never)

// Right after we finished writing, we don't want to GC yet with a one-minute TTL.
cws.shouldQueue(false, 0.48, time.Duration(0), minuteTTL, ms)
cws.shouldQueue(false, 0.48, time.Duration(0), minuteTTL, ms, never)

// Neither after a minute. The first values are about to become GC'able, though.
cws.shouldQueue(false, 1.46, time.Minute, minuteTTL, ms)
// After a minute score is already above minimum threshold and some data is
// GC able so it triggers shouldQueue if there were no GC runs recently
// enough, but not queueable if GC run recently.
cws.shouldQueue(true, 1.46, time.Minute, minuteTTL, ms, never)
cws.shouldQueue(false, 1.46, time.Minute, minuteTTL, ms, 30*time.Second)
// 90 seconds in it's really close, but still just shy of GC. Half of the
// values could be deleted now (remember that we wrote them over a one
// minute period).
cws.shouldQueue(false, 1.95, 3*time.Minute/2, minuteTTL, ms)
// We are close to high threshold, so cooldown time shrunk to just under 6
// minutes.
cws.shouldQueue(true, 1.95, 3*time.Minute/2, minuteTTL, ms, 6*time.Minute)
cws.shouldQueue(false, 1.95, 3*time.Minute/2, minuteTTL, ms, 5*time.Minute)
// Advancing another 1/4 minute does the trick.
cws.shouldQueue(true, 2.20, 7*time.Minute/4, minuteTTL, ms)
cws.shouldQueue(true, 2.20, 7*time.Minute/4, minuteTTL, ms, never)
// After an hour, that's (of course) still true with a very high priority.
cws.shouldQueue(true, 59.34, time.Hour, minuteTTL, ms)
cws.shouldQueue(true, 59.34, time.Hour, minuteTTL, ms, never)

// Let's see what the same would look like with a 1h TTL.
// Can't delete anything until 59min have passed, and indeed the score is low.
cws.shouldQueue(false, 0.01, time.Duration(0), hourTTL, ms)
cws.shouldQueue(false, 0.02, time.Minute, hourTTL, ms)
cws.shouldQueue(false, 0.99, time.Hour, hourTTL, ms)
cws.shouldQueue(false, 0.01, time.Duration(0), hourTTL, ms, never)
cws.shouldQueue(false, 0.02, time.Minute, hourTTL, ms, never)
cws.shouldQueue(false, 0.99, time.Hour, hourTTL, ms, never)
// After 90 minutes, we're getting closer. After just over two hours,
// definitely ripe for GC (and this would delete all the values).
cws.shouldQueue(false, 1.48, 90*time.Minute, hourTTL, ms)
cws.shouldQueue(true, 2.05, 125*time.Minute, hourTTL, ms)
cws.shouldQueue(true, 1.48, 90*time.Minute, hourTTL, ms, never)
cws.shouldQueue(false, 1.48, 90*time.Minute, hourTTL, ms, 5*time.Minute)
cws.shouldQueue(true, 2.05, 125*time.Minute, hourTTL, ms, never)
}

{
Expand All @@ -435,7 +452,7 @@ func TestMVCCGCQueueMakeGCScoreRealistic(t *testing.T) {
cws.multiKey(999, valSize, nil /* no txn */, &ms)

// GC shouldn't move at all, even after a long time and short TTL.
cws.shouldQueue(false, 0, 24*time.Hour, minuteTTL, ms)
cws.shouldQueue(false, 0, 24*time.Hour, minuteTTL, ms, never)

// Write a single key twice.
cws.singleKeySteady(2, 0, valSize, &ms)
Expand All @@ -446,16 +463,16 @@ func TestMVCCGCQueueMakeGCScoreRealistic(t *testing.T) {

// If the fact that 99.9% of the replica is live were not taken into
// account, this would get us at least close to GC.
cws.shouldQueue(false, 0.00, 5*time.Minute, minuteTTL, ms)
cws.shouldQueue(false, 0.00, 5*time.Minute, minuteTTL, ms, never)

// 12 hours in the score becomes relevant, but not yet large enough.
// The key is of course GC'able and has been for a long time, but
// to find it we'd have to scan all the other kv pairs as well.
cws.shouldQueue(false, 0.71, 12*time.Hour, minuteTTL, ms)
cws.shouldQueue(false, 0.71, 12*time.Hour, minuteTTL, ms, never)

// Two days in we're more than ready to go, would queue for GC, and
// delete.
cws.shouldQueue(true, 2.85, 48*time.Hour, minuteTTL, ms)
cws.shouldQueue(true, 2.85, 48*time.Hour, minuteTTL, ms, never)
}

{
Expand All @@ -472,9 +489,12 @@ func TestMVCCGCQueueMakeGCScoreRealistic(t *testing.T) {
// doesn't matter. In reality, the value-based GC score will often strike first.
cws.multiKey(100, valSize, txn, &ms)

cws.shouldQueue(false, 0.12, 1*time.Hour, irrelevantTTL, ms)
cws.shouldQueue(false, 0.87, 7*time.Hour, irrelevantTTL, ms)
cws.shouldQueue(true, 1.12, 9*time.Hour, irrelevantTTL, ms)
cws.shouldQueue(false, 0.12, 1*time.Hour, irrelevantTTL, ms, never)
cws.shouldQueue(false, 0.87, 7*time.Hour, irrelevantTTL, ms, never)
cws.shouldQueue(true, 1.12, 9*time.Hour, irrelevantTTL, ms, never)
// Check if cooldown policy protects us from too frequent runs based on
// intents alone.
cws.shouldQueue(false, 1.12, 9*time.Hour, irrelevantTTL, ms, time.Hour)
}
}

Expand Down Expand Up @@ -524,7 +544,7 @@ func TestFullRangeDeleteHeuristic(t *testing.T) {

shouldQueueAfter := func(ms enginepb.MVCCStats, delay time.Duration, gcTTL time.Duration) bool {
now := deletionTime.Add(delay.Nanoseconds(), 0)
r := makeMVCCGCQueueScoreImpl(ctx, 0 /* seed */, now, ms, gcTTL, hlc.Timestamp{}, true,
r := makeMVCCGCQueueScoreImpl(ctx, 0 /* seed */, now, ms, gcTTL, now.Add(-time.Hour.Nanoseconds(), 0), true,
roachpb.GCHint{}, time.Hour)
return r.ShouldQueue
}
Expand Down