21227: Don't reduce outgoing request concurrency below 4.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>

diff --git a/sdk/go/arvados/limiter.go b/sdk/go/arvados/limiter.go
index dc944160ab2dd5d459a31fa2386ebe9a5f6bb2c3..9edc5386a7655c3f1d9e31bcb0d3f55b2a999c87 100644 (file)
--- a/sdk/go/arvados/limiter.go
+++ b/sdk/go/arvados/limiter.go
@@ -16,6 +16,7 @@ import (
 var (
        requestLimiterQuietPeriod        = time.Second
        requestLimiterInitialLimit int64 = 8
+       requestLimiterMinimumLimit int64 = 4
 )
 
 type requestLimiter struct {
@@ -145,6 +146,12 @@ func (rl *requestLimiter) Report(resp *http.Response, err error) bool {
                if max := rl.current * 2; max < rl.limit {
                        rl.limit = max
                }
+               if min := requestLimiterMinimumLimit; min > rl.limit {
+                       // If limit is too low, programs like
+                       // controller and test suites can end up with
+                       // too few slots to complete a single request.
+                       rl.limit = min
+               }
                if rl.maxlimit > 0 && rl.maxlimit < rl.limit {
                        rl.limit = rl.maxlimit
                }