sqlccl: rate limit presplitRanges in RESTORE

On clusters of more than 1 node, dumping all 16000 splits at once (more
or less) would consistenly get the cluster stuck in some state it never
got out of. Given that our normal codepaths probably weren't designed
with this sort of abuse in mind, spread the splits out a bit.

For cockroachdb#14792.

pkg/ccl/sqlccl/restore.go

@@ -12,6 +12,7 @@ import (
 	"github.com/pkg/errors"
 	"golang.org/x/net/context"
 	"golang.org/x/sync/errgroup"
+	"golang.org/x/time/rate"
 
 	"github.com/cockroachdb/cockroach/pkg/ccl/storageccl"
 	"github.com/cockroachdb/cockroach/pkg/ccl/utilccl"
@@ -479,14 +480,26 @@ func presplitRanges(baseCtx context.Context, db client.DB, input []roachpb.Key)
 
 	ctx, span := tracing.ChildSpan(baseCtx, "presplitRanges")
 	defer tracing.FinishSpan(span)
+	log.Infof(ctx, "presplitting %d ranges", len(input))
 
 	if len(input) == 0 {
 		return nil
 	}
 
+	// 100 was picked because it's small enough to work with on a 3-node cluster
+	// on my laptop and large enough that it only takes a couple minutes to
+	// presplit for a ~16000 range dataset.
+	// TODO(dan): See if there's some better solution #14798.
+	const splitsPerSecond, splitsBurst = 100, 1
+	limiter := rate.NewLimiter(splitsPerSecond, splitsBurst)
+
 	g, ctx := errgroup.WithContext(ctx)
 	var splitFn func([]roachpb.Key) error
 	splitFn = func(splitPoints []roachpb.Key) error {
+		if err := limiter.Wait(ctx); err != nil {
+			return err
+		}
+
 		// Pick the index such that it's 0 if len(splitPoints) == 1.
 		splitIdx := len(splitPoints) / 2
 		// AdminSplit requires that the key be a valid table key, which means