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Implement TTL for cached datasource instances #1230

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4110d1d
WIP: Implementing TTL for cached datasource instances
iwysiu Feb 12, 2025
2ccc384
increase expiration timeout
iwysiu Apr 15, 2025
a3ed029
fix race condition in test
iwysiu Apr 17, 2025
5c2a1ba
Merge remote-tracking branch 'origin/main' into iwysiu/ds/329
iwysiu Jun 13, 2025
521ca10
fixes for feedback
iwysiu Jun 13, 2025
3ad2374
Implement idle time TTL and reduce TTL
njvrzm Jul 24, 2025
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50 changes: 31 additions & 19 deletions backend/instancemgmt/instance_manager.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,14 +2,15 @@ package instancemgmt

import (
"context"
"fmt"
"reflect"
"sync"
"time"

"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promauto"

"github.com/grafana/grafana-plugin-sdk-go/backend"
gocache "github.com/patrickmn/go-cache"
)

var (
Expand All @@ -18,7 +19,10 @@ var (
Name: "active_instances",
Help: "The number of active plugin instances",
})
disposeTTL = 5 * time.Second
defaultDisposeTTL = 5 * time.Second

defaultInstanceTTL = 1 * time.Hour
defaultInstanceCleanup = 2 * time.Hour
)

// Instance is a marker interface for an instance.
Expand Down Expand Up @@ -73,21 +77,35 @@ type InstanceProvider interface {

// New create a new instance manager.
func New(provider InstanceProvider) InstanceManager {
return NewWithOptions(provider, defaultInstanceTTL, defaultInstanceCleanup, defaultDisposeTTL)
}

func NewWithOptions(provider InstanceProvider, instanceTTL, instanceCleanup, disposeTTL time.Duration) InstanceManager {
if provider == nil {
panic("provider cannot be nil")
}
cache := gocache.New(instanceTTL, instanceCleanup)
cache.OnEvicted(func(_ string, i interface{}) {
ci := i.(CachedInstance)
if disposer, valid := ci.instance.(InstanceDisposer); valid {
time.AfterFunc(disposeTTL, func() {
disposer.Dispose()
})
}
activeInstances.Dec()
})

return &instanceManager{
provider: provider,
cache: sync.Map{},
cache: cache,
locker: newLocker(),
}
}

type instanceManager struct {
locker *locker
provider InstanceProvider
cache sync.Map
cache *gocache.Cache
}

func (im *instanceManager) Get(ctx context.Context, pluginContext backend.PluginContext) (Instance, error) {
Expand All @@ -96,45 +114,39 @@ func (im *instanceManager) Get(ctx context.Context, pluginContext backend.Plugin
return nil, err
}
// Double-checked locking for update/create criteria
im.locker.RLock(cacheKey)
item, ok := im.cache.Load(cacheKey)
im.locker.RUnlock(cacheKey)
strKey := fmt.Sprintf("%v", cacheKey)
item, ok := im.cache.Get(strKey)

if ok {
ci := item.(CachedInstance)
needsUpdate := im.provider.NeedsUpdate(ctx, pluginContext, ci)

if !needsUpdate {
im.cache.SetDefault(strKey, ci)
return ci.instance, nil
}
}

im.locker.Lock(cacheKey)
defer im.locker.Unlock(cacheKey)
im.locker.Lock(strKey)
defer im.locker.Unlock(strKey)

if item, ok := im.cache.Load(cacheKey); ok {
if item, ok := im.cache.Get(strKey); ok {
ci := item.(CachedInstance)
needsUpdate := im.provider.NeedsUpdate(ctx, pluginContext, ci)

if !needsUpdate {
im.cache.SetDefault(strKey, ci)
return ci.instance, nil
}

if disposer, valid := ci.instance.(InstanceDisposer); valid {
time.AfterFunc(disposeTTL, func() {
disposer.Dispose()
activeInstances.Dec()
})
} else {
activeInstances.Dec()
}
im.cache.Delete(strKey)
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It may be a little faster to avoid this delete, make a function for the disposer code, and call that function from here and in the OnEvicted handler.

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I think the added complexity probably isn't worth it here - Delete here does acquire a lock, but we'll only hit this code path when the datasource config or Grafana config are updated, so quite rarely in the scheme of things.

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Leaving it as is for now. This code shouldn't run that often so I'm not sure we'd see that much of a speed improvement

}

instance, err := im.provider.NewInstance(ctx, pluginContext)
if err != nil {
return nil, err
}
im.cache.Store(cacheKey, CachedInstance{
im.cache.SetDefault(strKey, CachedInstance{
PluginContext: pluginContext,
instance: instance,
})
Expand Down
53 changes: 40 additions & 13 deletions backend/instancemgmt/instance_manager_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,7 @@ func TestInstanceManager(t *testing.T) {
}

tip := &testInstanceProvider{}
im := New(tip)
im := NewWithOptions(tip, defaultInstanceTTL, defaultInstanceCleanup, time.Millisecond)

t.Run("When getting instance should create a new instance", func(t *testing.T) {
instance, err := im.Get(ctx, pCtx)
Expand All @@ -43,11 +43,6 @@ func TestInstanceManager(t *testing.T) {
Updated: time.Now(),
},
}
origDisposeTTL := disposeTTL
disposeTTL = time.Millisecond
t.Cleanup(func() {
disposeTTL = origDisposeTTL
})
newInstance, err := im.Get(ctx, pCtxUpdated)

t.Run("New instance should be created", func(t *testing.T) {
Expand All @@ -70,6 +65,44 @@ func TestInstanceManager(t *testing.T) {
})
}

func TestInstanceManagerExpiration(t *testing.T) {
ctx := context.Background()
pCtx := backend.PluginContext{
OrgID: 1,
AppInstanceSettings: &backend.AppInstanceSettings{
Updated: time.Now(),
},
}

tip := &testInstanceProvider{}
im := NewWithOptions(tip, time.Millisecond, 2*time.Millisecond, 10*time.Millisecond)

instance, err := im.Get(ctx, pCtx)
require.NoError(t, err)
require.NotNil(t, instance)
require.Equal(t, pCtx.OrgID, instance.(*testInstance).orgID)
require.Equal(t, pCtx.AppInstanceSettings.Updated, instance.(*testInstance).updated)

t.Run("After expiration", func(t *testing.T) {
instance.(*testInstance).wg.Wait()
require.True(t, instance.(*testInstance).disposed.Load())
require.Equal(t, int64(1), instance.(*testInstance).disposedTimes.Load())

newInstance, err := im.Get(ctx, pCtx)

t.Run("New instance should be created", func(t *testing.T) {
require.NoError(t, err)
require.NotNil(t, newInstance)
require.Equal(t, pCtx.OrgID, newInstance.(*testInstance).orgID)
require.Equal(t, pCtx.AppInstanceSettings.Updated, newInstance.(*testInstance).updated)
})

t.Run("New instance should not be the same as old instance", func(t *testing.T) {
require.NotSame(t, instance, newInstance)
})
})
}

func TestInstanceManagerConcurrency(t *testing.T) {
t.Run("Check possible race condition issues when initially creating instance", func(t *testing.T) {
ctx := context.Background()
Expand Down Expand Up @@ -110,12 +143,6 @@ func TestInstanceManagerConcurrency(t *testing.T) {
})

t.Run("Check possible race condition issues when re-creating instance on settings update", func(t *testing.T) {
origDisposeTTL := disposeTTL
disposeTTL = time.Millisecond
t.Cleanup(func() {
disposeTTL = origDisposeTTL
})

ctx := context.Background()
initialPCtx := backend.PluginContext{
OrgID: 1,
Expand All @@ -124,7 +151,7 @@ func TestInstanceManagerConcurrency(t *testing.T) {
},
}
tip := &testInstanceProvider{}
im := New(tip)
im := NewWithOptions(tip, defaultInstanceTTL, defaultInstanceCleanup, time.Millisecond)
// Creating initial instance with old contexts
instanceToDispose, _ := im.Get(ctx, initialPCtx)

Expand Down
1 change: 1 addition & 0 deletions go.mod
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,7 @@ require (
github.com/oasdiff/yaml3 v0.0.0-20250309153720-d2182401db90 // indirect
github.com/oklog/run v1.0.0 // indirect
github.com/oklog/ulid v1.3.1 // indirect
github.com/patrickmn/go-cache v2.1.0+incompatible
github.com/perimeterx/marshmallow v1.1.5 // indirect
github.com/pierrec/lz4/v4 v4.1.22 // indirect
github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
Expand Down
2 changes: 2 additions & 0 deletions go.sum
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,8 @@ github.com/oklog/ulid v1.3.1 h1:EGfNDEx6MqHz8B3uNV6QAib1UR2Lm97sHi3ocA6ESJ4=
github.com/oklog/ulid v1.3.1/go.mod h1:CirwcVhetQ6Lv90oh/F+FBtV6XMibvdAFo93nm5qn4U=
github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=
github.com/olekukonko/tablewriter v0.0.5/go.mod h1:hPp6KlRPjbx+hW8ykQs1w3UBbZlj6HuIJcUGPhkA7kY=
github.com/patrickmn/go-cache v2.1.0+incompatible h1:HRMgzkcYKYpi3C8ajMPV8OFXaaRUnok+kx1WdO15EQc=
github.com/patrickmn/go-cache v2.1.0+incompatible/go.mod h1:3Qf8kWWT7OJRJbdiICTKqZju1ZixQ/KpMGzzAfe6+WQ=
github.com/perimeterx/marshmallow v1.1.5 h1:a2LALqQ1BlHM8PZblsDdidgv1mWi1DgC2UmX50IvK2s=
github.com/perimeterx/marshmallow v1.1.5/go.mod h1:dsXbUu8CRzfYP5a87xpp0xq9S3u0Vchtcl8we9tYaXw=
github.com/pierrec/lz4/v4 v4.1.22 h1:cKFw6uJDK+/gfw5BcDL0JL5aBsAFdsIT18eRtLj7VIU=
Expand Down