Make maximum pending request configurable

This also bumps up the default to be 50 queued requests
instead of 10.

docs/faq.md

@@ -232,3 +232,9 @@ curl http://localhost:11434/api/generate -d '{"model": "llama3", "keep_alive": 0
 Alternatively, you can change the amount of time all models are loaded into memory by setting the `OLLAMA_KEEP_ALIVE` environment variable when starting the Ollama server. The `OLLAMA_KEEP_ALIVE` variable uses the same parameter types as the `keep_alive` parameter types mentioned above. Refer to section explaining [how to configure the Ollama server](#how-do-i-configure-ollama-server) to correctly set the environment variable.
 
 If you wish to override the `OLLAMA_KEEP_ALIVE` setting, use the `keep_alive` API parameter with the `/api/generate` or `/api/chat` API endpoints.
+
+## How do I manage the maximum number of requests the server can queue
+
+If too many requests are sent to the server, it will respond with a 503 error
+indicating the server is overloaded.  You can adjust how many requests may be
+queue by setting `OLLAMA_MAX_QUEUE`

server/routes.go

@@ -146,12 +146,7 @@ func (s *Server) GenerateHandler(c *gin.Context) {
 	select {
 	case runner = <-rCh:
 	case err = <-eCh:
-		if errors.Is(err, context.Canceled) {
-			c.JSON(499, gin.H{"error": "request canceled"})
-			return
-		}
-
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		handleErrorResponse(c, err)
 		return
 	}
 
@@ -394,12 +389,7 @@ func (s *Server) EmbeddingsHandler(c *gin.Context) {
 	select {
 	case runner = <-rCh:
 	case err = <-eCh:
-		if errors.Is(err, context.Canceled) {
-			c.JSON(499, gin.H{"error": "request canceled"})
-			return
-		}
-
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		handleErrorResponse(c, err)
 		return
 	}
 
@@ -1212,12 +1202,7 @@ func (s *Server) ChatHandler(c *gin.Context) {
 	select {
 	case runner = <-rCh:
 	case err = <-eCh:
-		if errors.Is(err, context.Canceled) {
-			c.JSON(499, gin.H{"error": "request canceled"})
-			return
-		}
-
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		handleErrorResponse(c, err)
 		return
 	}
 
@@ -1338,3 +1323,15 @@ func (s *Server) ChatHandler(c *gin.Context) {
 
 	streamResponse(c, ch)
 }
+
+func handleErrorResponse(c *gin.Context, err error) {
+	if errors.Is(err, context.Canceled) {
+		c.JSON(499, gin.H{"error": "request canceled"})
+		return
+	}
+	if errors.Is(err, ErrMaxQueue) {
+		c.JSON(http.StatusServiceUnavailable, gin.H{"error": err.Error()})
+		return
+	}
+	c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+}

server/sched.go

@@ -43,10 +43,13 @@ type Scheduler struct {
 	getGpuFn    func() gpu.GpuInfoList
 }
 
-// TODO set this to zero after a release or two, to enable multiple models by default
-var loadedMax = 1          // Maximum runners; < 1 maps to as many as will fit in VRAM (unlimited for CPU runners)
-var maxQueuedRequests = 10 // TODO configurable
-var numParallel = 1
+var (
+	// TODO set this to zero after a release or two, to enable multiple models by default
+	loadedMax         = 1 // Maximum runners; < 1 maps to as many as will fit in VRAM (unlimited for CPU runners)
+	maxQueuedRequests = 512
+	numParallel       = 1
+	ErrMaxQueue       = fmt.Errorf("server busy, please try again.  maximum pending requests exceeded")
+)
 
 func InitScheduler(ctx context.Context) *Scheduler {
 	maxRunners := os.Getenv("OLLAMA_MAX_LOADED_MODELS")
@@ -66,6 +69,14 @@ func InitScheduler(ctx context.Context) *Scheduler {
 			numParallel = p
 		}
 	}
+	if onp := os.Getenv("OLLAMA_MAX_QUEUE"); onp != "" {
+		p, err := strconv.Atoi(onp)
+		if err != nil || p <= 0 {
+			slog.Error("invalid setting", "OLLAMA_MAX_QUEUE", onp, "error", err)
+		} else {
+			maxQueuedRequests = p
+		}
+	}
 
 	sched := &Scheduler{
 		pendingReqCh:  make(chan *LlmRequest, maxQueuedRequests),
@@ -95,7 +106,7 @@ func (s *Scheduler) GetRunner(c context.Context, model *Model, opts api.Options,
 	select {
 	case s.pendingReqCh <- req:
 	default:
-		req.errCh <- fmt.Errorf("server busy, please try again.  maximum pending requests exceeded")
+		req.errCh <- ErrMaxQueue
 	}
 	return req.successCh, req.errCh
 }