Add CacheLatestTtlSecs to allow expiration of latest schemas (#1106)

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* chore: update repo semaphore config

* Add CacheLatestTtlSecs to allow expiration of latest schemas

* Fix golint

* Add runtime finalizer to stop ticker

---------

Co-authored-by: Confluent Jenkins Bot <jenkins@confluent.io>

Author: rayokota

schemaregistry/cache/cache.go

@@ -37,6 +37,8 @@ type Cache interface {
 	// Parameters:
 	//  * `key` - the key to delete
 	Delete(key interface{})
+	// Clear clears the cache
+	Clear()
 	// ToMap returns the current cache entries copied into a map
 	ToMap() map[interface{}]interface{}
 }

schemaregistry/cache/lrucache.go

@@ -131,6 +131,19 @@ func (c *LRUCache) Delete(key interface{}) {
 	}
 }
 
+// Clear clears the cache
+func (c *LRUCache) Clear() {
+	c.cacheLock.Lock()
+	for key, value := range c.lruElements {
+		delete(c.lruElements, key)
+		c.lruKeys.Remove(value)
+	}
+	for key := range c.entries {
+		delete(c.entries, key)
+	}
+	c.cacheLock.Unlock()
+}
+
 // ToMap returns the current cache entries copied into a map
 func (c *LRUCache) ToMap() map[interface{}]interface{} {
 	ret := make(map[interface{}]interface{})

schemaregistry/cache/mapcache.go

@@ -57,6 +57,13 @@ func (c *MapCache) Delete(key interface{}) {
 	delete(c.entries, key)
 }
 
+// Clear clears the cache
+func (c *MapCache) Clear() {
+	for key := range c.entries {
+		delete(c.entries, key)
+	}
+}
+
 // ToMap returns the current cache entries copied into a map
 func (c *MapCache) ToMap() map[interface{}]interface{} {
 	ret := make(map[interface{}]interface{})

schemaregistry/config.go

@@ -62,6 +62,8 @@ type Config struct {
 	RequestTimeoutMs int
 	// CacheCapacity positive integer or zero for unbounded capacity
 	CacheCapacity int
+	// CacheLatestTTLSecs ttl in secs for caching the latest schema
+	CacheLatestTTLSecs int
 
 	// HTTP client
 	HTTPClient *http.Client

schemaregistry/schemaregistry_client.go

@@ -20,8 +20,10 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/url"
+	"runtime"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/confluentinc/confluent-kafka-go/v2/schemaregistry/cache"
 )
@@ -189,6 +191,9 @@ type client struct {
 	schemaToVersionCacheLock sync.RWMutex
 	versionToSchemaCache     cache.Cache
 	versionToSchemaCacheLock sync.RWMutex
+	latestToSchemaCache      cache.Cache
+	latestToSchemaCacheLock  sync.RWMutex
+	evictor                  *evictor
 }
 
 var _ Client = new(client)
@@ -243,6 +248,7 @@ func NewClient(conf *Config) (Client, error) {
 	var idToSchemaCache cache.Cache
 	var schemaToVersionCache cache.Cache
 	var versionToSchemaCache cache.Cache
+	var latestToSchemaCache cache.Cache
 	if conf.CacheCapacity != 0 {
 		schemaToIDCache, err = cache.NewLRUCache(conf.CacheCapacity)
 		if err != nil {
@@ -260,18 +266,28 @@ func NewClient(conf *Config) (Client, error) {
 		if err != nil {
 			return nil, err
 		}
+		latestToSchemaCache, err = cache.NewLRUCache(conf.CacheCapacity)
+		if err != nil {
+			return nil, err
+		}
 	} else {
 		schemaToIDCache = cache.NewMapCache()
 		idToSchemaCache = cache.NewMapCache()
 		schemaToVersionCache = cache.NewMapCache()
 		versionToSchemaCache = cache.NewMapCache()
+		latestToSchemaCache = cache.NewMapCache()
 	}
 	handle := &client{
 		restService:          restService,
 		schemaToIDCache:      schemaToIDCache,
 		idToSchemaCache:      idToSchemaCache,
 		schemaToVersionCache: schemaToVersionCache,
 		versionToSchemaCache: versionToSchemaCache,
+		latestToSchemaCache:  latestToSchemaCache,
+	}
+	if conf.CacheLatestTTLSecs > 0 {
+		runEvictor(handle, time.Duration(conf.CacheLatestTTLSecs)*time.Second)
+		runtime.SetFinalizer(handle, stopEvictor)
 	}
 	return handle, nil
 }
@@ -393,7 +409,26 @@ func (c *client) GetID(subject string, schema SchemaInfo, normalize bool) (id in
 // GetLatestSchemaMetadata fetches latest version registered with the provided subject
 // Returns SchemaMetadata object
 func (c *client) GetLatestSchemaMetadata(subject string) (result SchemaMetadata, err error) {
-	return c.GetSchemaMetadata(subject, -1)
+	c.latestToSchemaCacheLock.RLock()
+	metadataValue, ok := c.latestToSchemaCache.Get(subject)
+	c.latestToSchemaCacheLock.RUnlock()
+	if ok {
+		return *metadataValue.(*SchemaMetadata), nil
+	}
+
+	c.latestToSchemaCacheLock.Lock()
+	// another goroutine could have already put it in cache
+	metadataValue, ok = c.latestToSchemaCache.Get(subject)
+	if !ok {
+		err = c.restService.handleRequest(newRequest("GET", versions, nil, url.PathEscape(subject), "latest"), &result)
+		if err == nil {
+			c.latestToSchemaCache.Put(subject, &result)
+		}
+	} else {
+		result = *metadataValue.(*SchemaMetadata)
+	}
+	c.latestToSchemaCacheLock.Unlock()
+	return result, err
 }
 
 // GetSchemaMetadata fetches the requested subject schema identified by version
@@ -687,3 +722,34 @@ func (c *client) UpdateDefaultCompatibility(update Compatibility) (compatibility
 
 	return result.CompatibilityUpdate, err
 }
+
+type evictor struct {
+	Interval time.Duration
+	stop     chan bool
+}
+
+func (e *evictor) Run(c cache.Cache) {
+	ticker := time.NewTicker(e.Interval)
+	for {
+		select {
+		case <-ticker.C:
+			c.Clear()
+		case <-e.stop:
+			ticker.Stop()
+			return
+		}
+	}
+}
+
+func stopEvictor(c *client) {
+	c.evictor.stop <- true
+}
+
+func runEvictor(c *client, ci time.Duration) {
+	e := &evictor{
+		Interval: ci,
+		stop:     make(chan bool),
+	}
+	c.evictor = e
+	go e.Run(c.latestToSchemaCache)
+}