Use fnv32a hash for user_subring

CHANGELOG.md

@@ -68,6 +68,7 @@
 * [BUGFIX] Experimental Delete Series: Fixed a data race in Purger. #2817
 * [BUGFIX] KV: Fixed a bug that triggered a panic due to metrics being registered with the same name but different labels when using a `multi` configured KV client. #2837
 * [BUGFIX] Query-frontend: Fix passing HTTP `Host` header if `-frontend.downstream-url` is configured. #2880
+* [BUGFIX] Ingester: Improve time-series distribution when `-experimental.distributor.user-subring-size` is enabled. #2887
 
 ## 1.2.0 / 2020-07-01
 

pkg/distributor/distributor.go

@@ -512,7 +512,7 @@ func (d *Distributor) Push(ctx context.Context, req *client.WriteRequest) (*clie
 
 	// Obtain a subring if required
 	if size := d.limits.SubringSize(userID); size > 0 {
-		h := client.HashAdd32(client.HashNew32(), userID)
+		h := client.HashAdd32a(client.HashNew32a(), userID)
 		subRing, err = d.ingestersRing.Subring(h, size)
 		if err != nil {
 			return nil, httpgrpc.Errorf(http.StatusInternalServerError, "unable to create subring: %v", err)

pkg/ingester/client/fnv.go

@@ -75,3 +75,25 @@ func HashAddByte32(h uint32, b byte) uint32 {
 	h ^= uint32(b)
 	return h
 }
+
+// HashNew32a initializies a new fnv32a hash value.
+func HashNew32a() uint32 {
+	return offset32
+}
+
+// HashAdd32a adds a string to a fnv32a hash value, returning the updated hash.
+// Note this is the same algorithm as Go stdlib `sum32.Write()`
+func HashAdd32a(h uint32, s string) uint32 {
+	for i := 0; i < len(s); i++ {
+		h ^= uint32(s[i])
+		h *= prime32
+	}
+	return h
+}
+
+// HashAddByte32a adds a byte to a fnv32a hash value, returning the updated hash.
+func HashAddByte32a(h uint32, b byte) uint32 {
+	h ^= uint32(b)
+	h *= prime32
+	return h
+}