Use a cache instead of sync.Pool in script processor (elastic#19562)

This updates the script processor to keep a simple cache of Javascript VM sessions instead of relying on sync.Pool for this task. The size of this cache can be controlled by the new `max_cached_sessions` option. The reasoning behind this change is to avoid sync.Pool discarding and re-allocating new sessions every garbage collection cycle. For large Javascript pipelines, allocating a new session is a very expensive operation that can take hundreds of milliseconds or even seconds to complete. This has a severe impact in ingestion rates.
adriansr · Jul 7, 2020 · 7930f9e · 7930f9e
1 parent 5c719cf
commit 7930f9e
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diff --git a/CHANGELOG.next.asciidoc b/CHANGELOG.next.asciidoc
@@ -323,6 +323,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Add the `ignore_failure` configuration option to the dissect processor. {pull}19464[19464]
 - Add the `overwrite_keys` configuration option to the dissect processor. {pull}19464[19464]
 - Add support to trim captured values in the dissect processor. {pull}19464[19464]
+- Added the `max_cached_sessions` option to the script processor. {pull}19562[19562]
 
 *Auditbeat*
 

diff --git a/libbeat/processors/script/docs/script.asciidoc b/libbeat/processors/script/docs/script.asciidoc
@@ -113,6 +113,9 @@ is interrupted. You can set this option to prevent a script from running for
 too long (like preventing an infinite `while` loop). By default there is no
 timeout.
 
+`max_cached_sessions`:: This sets the maximum number of Javascript VM sessions
+that will be cached to avoid reallocation. The default is `4`.
+
 [float]
 ==== Event API
 

diff --git a/libbeat/processors/script/javascript/config.go b/libbeat/processors/script/javascript/config.go
@@ -25,13 +25,14 @@ import (
 
 // Config defines the Javascript source files to use for the processor.
 type Config struct {
-	Tag            string                 `config:"tag"`                      // Processor ID for debug and metrics.
-	Source         string                 `config:"source"`                   // Inline script to execute.
-	File           string                 `config:"file"`                     // Source file.
-	Files          []string               `config:"files"`                    // Multiple source files.
-	Params         map[string]interface{} `config:"params"`                   // Parameters to pass to script.
-	Timeout        time.Duration          `config:"timeout" validate:"min=0"` // Execution timeout.
-	TagOnException string                 `config:"tag_on_exception"`         // Tag to add to events when an exception happens.
+	Tag               string                 `config:"tag"`                                  // Processor ID for debug and metrics.
+	Source            string                 `config:"source"`                               // Inline script to execute.
+	File              string                 `config:"file"`                                 // Source file.
+	Files             []string               `config:"files"`                                // Multiple source files.
+	Params            map[string]interface{} `config:"params"`                               // Parameters to pass to script.
+	Timeout           time.Duration          `config:"timeout" validate:"min=0"`             // Execution timeout.
+	TagOnException    string                 `config:"tag_on_exception"`                     // Tag to add to events when an exception happens.
+	MaxCachedSessions int                    `config:"max_cached_sessions" validate:"min=0"` // Max. number of cached VM sessions.
 }
 
 // Validate returns an error if one (and only one) option is not set.
@@ -57,6 +58,7 @@ func (c Config) Validate() error {
 
 func defaultConfig() Config {
 	return Config{
-		TagOnException: "_js_exception",
+		TagOnException:    "_js_exception",
+		MaxCachedSessions: 4,
 	}
 }
diff --git a/libbeat/processors/script/javascript/session.go b/libbeat/processors/script/javascript/session.go
@@ -19,7 +19,6 @@ package javascript
 
 import (
 	"reflect"
-	"sync"
 	"time"
 
 	"github.com/dop251/goja"
@@ -83,17 +82,25 @@ type session struct {
 }
 
 func newSession(p *goja.Program, conf Config, test bool) (*session, error) {
+	// Create a logger
+	logger := logp.NewLogger(logName)
+	if conf.Tag != "" {
+		logger = logger.With("instance_id", conf.Tag)
+	}
+	// Measure load times
+	start := time.Now()
+	defer func() {
+		took := time.Now().Sub(start)
+		logger.Debugf("Load of javascript pipeline took %v", took)
+	}()
 	// Setup JS runtime.
 	s := &session{
 		vm:             goja.New(),
-		log:            logp.NewLogger(logName),
+		log:            logger,
 		makeEvent:      newBeatEventV0,
 		timeout:        conf.Timeout,
 		tagOnException: conf.TagOnException,
 	}
-	if conf.Tag != "" {
-		s.log = s.log.With("instance_id", conf.Tag)
-	}
 
 	// Register modules.
 	for _, registerModule := range sessionHooks {
@@ -266,7 +273,8 @@ func init() {
 }
 
 type sessionPool struct {
-	pool *sync.Pool
+	New func() *session
+	C   chan *session
 }
 
 func newSessionPool(p *goja.Program, c Config) (*sessionPool, error) {
@@ -275,24 +283,32 @@ func newSessionPool(p *goja.Program, c Config) (*sessionPool, error) {
 		return nil, err
 	}
 
-	pool := &sync.Pool{
-		New: func() interface{} {
+	pool := sessionPool{
+		New: func() *session {
 			s, _ := newSession(p, c, false)
 			return s
 		},
+		C: make(chan *session, c.MaxCachedSessions),
 	}
 	pool.Put(s)
 
-	return &sessionPool{pool}, nil
+	return &pool, nil
 }
 
 func (p *sessionPool) Get() *session {
-	s, _ := p.pool.Get().(*session)
-	return s
+	select {
+	case s := <-p.C:
+		return s
+	default:
+		return p.New()
+	}
 }
 
 func (p *sessionPool) Put(s *session) {
 	if s != nil {
-		p.pool.Put(s)
+		select {
+		case p.C <- s:
+		default:
+		}
 	}
 }