From f3b5289610db5f0b54c73ff5ec0cd80e51f1ae94 Mon Sep 17 00:00:00 2001
From: Tom Clegg <tom@curii.com>
Date: Thu, 25 May 2023 11:25:02 -0400
Subject: [PATCH] 20511: Limit server-to-server client to 1/4 of API req
 capacity.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>
---
 sdk/go/arvados/client.go  | 11 ++++++-----
 sdk/go/arvados/limiter.go |  4 ++++
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/sdk/go/arvados/client.go b/sdk/go/arvados/client.go
index d1a87e30e8..6316d1beda 100644
--- a/sdk/go/arvados/client.go
+++ b/sdk/go/arvados/client.go
@@ -142,11 +142,12 @@ func NewClientFromConfig(cluster *Cluster) (*Client, error) {
 		}
 	}
 	return &Client{
-		Client:   hc,
-		Scheme:   ctrlURL.Scheme,
-		APIHost:  ctrlURL.Host,
-		Insecure: cluster.TLS.Insecure,
-		Timeout:  5 * time.Minute,
+		Client:         hc,
+		Scheme:         ctrlURL.Scheme,
+		APIHost:        ctrlURL.Host,
+		Insecure:       cluster.TLS.Insecure,
+		Timeout:        5 * time.Minute,
+		requestLimiter: requestLimiter{maxlimit: int64(cluster.API.MaxConcurrentRequests / 4)},
 	}, nil
 }
 
diff --git a/sdk/go/arvados/limiter.go b/sdk/go/arvados/limiter.go
index 0fc6cc0964..dc944160ab 100644
--- a/sdk/go/arvados/limiter.go
+++ b/sdk/go/arvados/limiter.go
@@ -21,6 +21,7 @@ var (
 type requestLimiter struct {
 	current    int64
 	limit      int64
+	maxlimit   int64
 	lock       sync.Mutex
 	cond       *sync.Cond
 	quietUntil time.Time
@@ -144,6 +145,9 @@ func (rl *requestLimiter) Report(resp *http.Response, err error) bool {
 		if max := rl.current * 2; max < rl.limit {
 			rl.limit = max
 		}
+		if rl.maxlimit > 0 && rl.maxlimit < rl.limit {
+			rl.limit = rl.maxlimit
+		}
 		rl.cond.Broadcast()
 	}
 	return false
-- 
2.30.2