service/storage_service: Add and use xxhash feature

We add a cluster feature that informs whether the xxHash algorithm is
supported, and allow nodes to switch to it. We use a cluster feature
because older versions are not ready to receive a different digest
algorithm than MD5 when answering a data request.

If we ever should add a new hash algorithm, we would also need to
add a new cluster feature for that algorithm. The alternative would be
to add code so a coordinator could negotiate what digest algorithm to
use with the set of replicas it is contacting.

Fixes #2884

Signed-off-by: Duarte Nunes <duarte@scylladb.com>

digest_algorithm.hh

@@ -25,8 +25,8 @@ namespace query {
 
 enum class digest_algorithm : uint8_t {
     none = 0,  // digest not required
-    MD5 = 1,   // default algorithm
-    xxHash = 2,
+    MD5 = 1,
+    xxHash = 2,// default algorithm
 };
 
 }

idl/query.idl.hh

@@ -31,7 +31,8 @@ class query_result stub [[writable]] {
 
 enum class digest_algorithm : uint8_t {
     none = 0,  // digest not required
-    MD5 = 1,   // default algorithm
+    MD5 = 1,
+    xxHash = 2,// default algorithm
 };
 
 }

service/storage_proxy.cc

@@ -2457,7 +2457,9 @@ public:
 };
 
 query::digest_algorithm digest_algorithm() {
-    return query::digest_algorithm::MD5;
+    return service::get_local_storage_service().cluster_supports_xxhash_digest_algorithm()
+         ? query::digest_algorithm::xxHash
+         : query::digest_algorithm::MD5;
 }
 
 class abstract_read_executor : public enable_shared_from_this<abstract_read_executor> {

service/storage_service.cc

@@ -92,6 +92,7 @@ static const sstring CORRECT_COUNTER_ORDER_FEATURE = "CORRECT_COUNTER_ORDER";
 static const sstring SCHEMA_TABLES_V3 = "SCHEMA_TABLES_V3";
 static const sstring CORRECT_NON_COMPOUND_RANGE_TOMBSTONES = "CORRECT_NON_COMPOUND_RANGE_TOMBSTONES";
 static const sstring WRITE_FAILURE_REPLY_FEATURE = "WRITE_FAILURE_REPLY";
+static const sstring XXHASH_FEATURE = "XXHASH";
 
 distributed<storage_service> _the_storage_service;
 
@@ -139,6 +140,7 @@ sstring storage_service::get_config_supported_features() {
         SCHEMA_TABLES_V3,
         CORRECT_NON_COMPOUND_RANGE_TOMBSTONES,
         WRITE_FAILURE_REPLY_FEATURE,
+        XXHASH_FEATURE,
     };
     if (service::get_local_storage_service()._db.local().get_config().experimental()) {
         features.push_back(MATERIALIZED_VIEWS_FEATURE);
@@ -351,6 +353,7 @@ void storage_service::register_features() {
     _schema_tables_v3 = gms::feature(SCHEMA_TABLES_V3);
     _correct_non_compound_range_tombstones = gms::feature(CORRECT_NON_COMPOUND_RANGE_TOMBSTONES);
     _write_failure_reply_feature = gms::feature(WRITE_FAILURE_REPLY_FEATURE);
+    _xxhash_feature = gms::feature(XXHASH_FEATURE);
 
     if (_db.local().get_config().experimental()) {
         _materialized_views_feature = gms::feature(MATERIALIZED_VIEWS_FEATURE);

service/storage_service.hh

@@ -275,6 +275,7 @@ private:
     gms::feature _schema_tables_v3;
     gms::feature _correct_non_compound_range_tombstones;
     gms::feature _write_failure_reply_feature;
+    gms::feature _xxhash_feature;
 public:
     void enable_all_features() {
         _range_tombstones_feature.enable();
@@ -287,6 +288,7 @@ public:
         _schema_tables_v3.enable();
         _correct_non_compound_range_tombstones.enable();
         _write_failure_reply_feature.enable();
+        _xxhash_feature.enable();
     }
 
     void finish_bootstrapping() {
@@ -2259,6 +2261,10 @@ public:
     bool cluster_supports_write_failure_reply() const {
         return bool(_write_failure_reply_feature);
     }
+
+    bool cluster_supports_xxhash_digest_algorithm() const {
+        return bool(_xxhash_feature);
+    }
 };
 
 inline future<> init_storage_service(distributed<database>& db, sharded<auth::service>& auth_service) {