clean expired cache entries periodically

Signed-off-by: Rudrakh Panigrahi <rudrakh97@gmail.com>

topdown/cache/cache.go

@@ -7,15 +7,20 @@ package cache
 
 import (
 	"container/list"
+	"fmt"
+	"math"
 	"sync"
+	"time"
 
 	"github.com/open-policy-agent/opa/ast"
 
 	"github.com/open-policy-agent/opa/util"
 )
 
 const (
-	defaultMaxSizeBytes = int64(0) // unlimited
+	defaultMaxSizeBytes                      = int64(0)   // unlimited
+	defaultForcedEvictionThresholdPercentage = int64(100) // trigger at max_size_bytes
+	defaultStaleEntryEvictionPeriodSeconds   = int64(0)   // never
 )
 
 // Config represents the configuration of the inter-query cache.
@@ -25,15 +30,21 @@ type Config struct {
 
 // InterQueryBuiltinCacheConfig represents the configuration of the inter-query cache that built-in functions can utilize.
 type InterQueryBuiltinCacheConfig struct {
-	MaxSizeBytes *int64 `json:"max_size_bytes,omitempty"`
+	MaxSizeBytes                      *int64 `json:"max_size_bytes,omitempty"`
+	ForcedEvictionThresholdPercentage *int64 `json:"forced_eviction_threshold_percentage,omitempty"`
+	StaleEntryEvictionPeriodSeconds   *int64 `json:"stale_entry_eviction_period_seconds,omitempty"`
 }
 
 // ParseCachingConfig returns the config for the inter-query cache.
 func ParseCachingConfig(raw []byte) (*Config, error) {
 	if raw == nil {
 		maxSize := new(int64)
 		*maxSize = defaultMaxSizeBytes
-		return &Config{InterQueryBuiltinCache: InterQueryBuiltinCacheConfig{MaxSizeBytes: maxSize}}, nil
+		threshold := new(int64)
+		*threshold = defaultForcedEvictionThresholdPercentage
+		period := new(int64)
+		*period = defaultStaleEntryEvictionPeriodSeconds
+		return &Config{InterQueryBuiltinCache: InterQueryBuiltinCacheConfig{MaxSizeBytes: maxSize, ForcedEvictionThresholdPercentage: threshold, StaleEntryEvictionPeriodSeconds: period}}, nil
 	}
 
 	var config Config
@@ -55,6 +66,26 @@ func (c *Config) validateAndInjectDefaults() error {
 		*maxSize = defaultMaxSizeBytes
 		c.InterQueryBuiltinCache.MaxSizeBytes = maxSize
 	}
+	if c.InterQueryBuiltinCache.ForcedEvictionThresholdPercentage == nil {
+		threshold := new(int64)
+		*threshold = defaultForcedEvictionThresholdPercentage
+		c.InterQueryBuiltinCache.ForcedEvictionThresholdPercentage = threshold
+	} else {
+		threshold := *c.InterQueryBuiltinCache.ForcedEvictionThresholdPercentage
+		if threshold < 0 || threshold > 100 {
+			return fmt.Errorf("invalid forced_eviction_threshold_percentage %v", threshold)
+		}
+	}
+	if c.InterQueryBuiltinCache.StaleEntryEvictionPeriodSeconds == nil {
+		period := new(int64)
+		*period = defaultStaleEntryEvictionPeriodSeconds
+		c.InterQueryBuiltinCache.StaleEntryEvictionPeriodSeconds = period
+	} else {
+		period := *c.InterQueryBuiltinCache.StaleEntryEvictionPeriodSeconds
+		if period < 0 {
+			return fmt.Errorf("invalid stale_entry_eviction_period_seconds %v", period)
+		}
+	}
 	return nil
 }
 
@@ -67,24 +98,40 @@ type InterQueryCacheValue interface {
 // InterQueryCache defines the interface for the inter-query cache.
 type InterQueryCache interface {
 	Get(key ast.Value) (value InterQueryCacheValue, found bool)
-	Insert(key ast.Value, value InterQueryCacheValue) int
+	Insert(key ast.Value, value InterQueryCacheValue, expiresAt time.Time) int
 	Delete(key ast.Value)
 	UpdateConfig(config *Config)
 	Clone(value InterQueryCacheValue) (InterQueryCacheValue, error)
 }
 
 // NewInterQueryCache returns a new inter-query cache.
 func NewInterQueryCache(config *Config) InterQueryCache {
-	return &cache{
+	iqCache := &cache{
 		items:  map[string]cacheItem{},
 		usage:  0,
 		config: config,
 		l:      list.New(),
 	}
+
+	// Start routine to clean up stale values once every StaleEntryEvictionPeriodSeconds
+	cleanupPeriod := iqCache.staleEntryEvictionTimePeriodSeconds()
+	if cleanupPeriod > 0 {
+		ticker := time.NewTicker(time.Duration(cleanupPeriod) * time.Second)
+		go func() {
+			defer ticker.Stop()
+			for {
+				<-ticker.C
+				iqCache.cleanStaleValues()
+			}
+		}()
+	}
+
+	return iqCache
 }
 
 type cacheItem struct {
 	value      InterQueryCacheValue
+	expiresAt  time.Time
 	keyElement *list.Element
 }
 
@@ -97,10 +144,10 @@ type cache struct {
 }
 
 // Insert inserts a key k into the cache with value v.
-func (c *cache) Insert(k ast.Value, v InterQueryCacheValue) (dropped int) {
+func (c *cache) Insert(k ast.Value, v InterQueryCacheValue, expiresAt time.Time) (dropped int) {
 	c.mtx.Lock()
 	defer c.mtx.Unlock()
-	return c.unsafeInsert(k, v)
+	return c.unsafeInsert(k, v, expiresAt)
 }
 
 // Get returns the value in the cache for k.
@@ -137,10 +184,9 @@ func (c *cache) Clone(value InterQueryCacheValue) (InterQueryCacheValue, error)
 	return c.unsafeClone(value)
 }
 
-func (c *cache) unsafeInsert(k ast.Value, v InterQueryCacheValue) (dropped int) {
+func (c *cache) unsafeInsert(k ast.Value, v InterQueryCacheValue, expiresAt time.Time) (dropped int) {
 	size := v.SizeInBytes()
-	limit := c.maxSizeBytes()
-
+	limit := int64(math.Ceil(float64(c.forcedEvictionThresholdPercentage())/100.0) * (float64(c.maxSizeBytes())))
 	if limit > 0 {
 		if size > limit {
 			dropped++
@@ -159,6 +205,7 @@ func (c *cache) unsafeInsert(k ast.Value, v InterQueryCacheValue) (dropped int)
 
 	c.items[k.String()] = cacheItem{
 		value:      v,
+		expiresAt:  expiresAt,
 		keyElement: c.l.PushBack(k),
 	}
 	c.usage += size
@@ -191,3 +238,32 @@ func (c *cache) maxSizeBytes() int64 {
 	}
 	return *c.config.InterQueryBuiltinCache.MaxSizeBytes
 }
+
+func (c *cache) forcedEvictionThresholdPercentage() int64 {
+	if c.config == nil {
+		return defaultForcedEvictionThresholdPercentage
+	}
+	return *c.config.InterQueryBuiltinCache.ForcedEvictionThresholdPercentage
+}
+
+func (c *cache) staleEntryEvictionTimePeriodSeconds() int64 {
+	if c.config == nil {
+		return defaultStaleEntryEvictionPeriodSeconds
+	}
+	return *c.config.InterQueryBuiltinCache.StaleEntryEvictionPeriodSeconds
+}
+
+func (c *cache) cleanStaleValues() (dropped int) {
+	c.mtx.Lock()
+	defer c.mtx.Unlock()
+	for key := c.l.Front(); key != nil; {
+		nextKey := key.Next()
+		// if expiresAt is zero, the item doesn't have an expiry
+		if ea := c.items[(key.Value.(ast.Value)).String()].expiresAt; !ea.IsZero() && ea.Before(time.Now()) {
+			c.unsafeDelete(key.Value.(ast.Value))
+			dropped++
+		}
+		key = nextKey
+	}
+	return dropped
+}