Add another tablet load balancer algorithm: random (#18787)

Signed-off-by: Nick Van Wiggeren <[email protected]>
Signed-off-by: Nick Van Wiggeren <[email protected]>
Co-authored-by: Tim Vaillancourt <[email protected]>

Author: nickvanw

go/flags/endtoend/vtgate.txt

@@ -28,8 +28,8 @@ Flags:
       --allow-kill-statement                                             Allows the execution of kill statement
       --allowed-tablet-types strings                                     Specifies the tablet types this vtgate is allowed to route queries to. Should be provided as a comma-separated set of tablet types.
       --alsologtostderr                                                  log to standard error as well as files
-      --balancer-keyspaces strings                                       When in balanced mode, a comma-separated list of keyspaces for which to use the balancer (optional)
-      --balancer-vtgate-cells strings                                    When in balanced mode, a comma-separated list of cells that contain vtgates (required)
+      --balancer-keyspaces strings                                       Comma-separated list of keyspaces for which to use the balancer (optional). If empty, applies to all keyspaces.
+      --balancer-vtgate-cells strings                                    Comma-separated list of cells that contain vttablets. For 'prefer-cell' mode, this is required. For 'random' mode, this is optional and filters tablets to those cells.
       --bind-address string                                              Bind address for the server. If empty, the server will listen on all available unicast and anycast IP addresses of the local system.
       --buffer-drain-concurrency int                                     Maximum number of requests retried simultaneously. More concurrency will increase the load on the PRIMARY vttablet when draining the buffer. (default 1)
       --buffer-keyspace-shards string                                    If not empty, limit buffering to these entries (comma separated). Entry format: keyspace or keyspace/shard. Requires --enable_buffer=true.
@@ -56,7 +56,7 @@ Flags:
       --discovery-high-replication-lag-minimum-serving duration          Threshold above which replication lag is considered too high when applying the min_number_serving_vttablets flag. (default 2h0m0s)
       --discovery-low-replication-lag duration                           Threshold below which replication lag is considered low enough to be healthy. (default 30s)
       --emit-stats                                                       If set, emit stats to push-based monitoring and stats backends
-      --enable-balancer                                                  Enable the tablet balancer to evenly spread query load for a given tablet type
+      --enable-balancer                                                  (DEPRECATED: use --vtgate-balancer-mode instead) Enable the tablet balancer to evenly spread query load for a given tablet type
       --enable-buffer                                                    Enable buffering (stalling) of primary traffic during failovers.
       --enable-buffer-dry-run                                            Detect and log failover events, but do not actually buffer requests.
       --enable-direct-ddl                                                Allow users to submit direct DDL statements (default true)
@@ -246,6 +246,7 @@ Flags:
   -v, --version                                                          print binary version
       --vmodule vModuleFlag                                              comma-separated list of pattern=N settings for file-filtered logging
       --vschema-ddl-authorized-users string                              List of users authorized to execute vschema ddl operations, or '%' to allow all users.
+      --vtgate-balancer-mode string                                      Tablet balancer mode (options: cell, prefer-cell, random). Defaults to 'cell' which shuffles tablets in the local cell.
       --vtgate-config-terse-errors                                       prevent bind vars from escaping in returned errors
       --warming-reads-concurrency int                                    Number of concurrent warming reads allowed (default 500)
       --warming-reads-percent int                                        Percentage of reads on the primary to forward to replicas. Useful for keeping buffer pools warm

go/test/endtoend/cluster/cluster_process.go

@@ -453,6 +453,7 @@ func (cluster *LocalProcessCluster) AddShard(keyspaceName string, shardName stri
 			HTTPPort:  cluster.GetAndReservePort(),
 			GrpcPort:  cluster.GetAndReservePort(),
 			MySQLPort: cluster.GetAndReservePort(),
+			Cell:      cluster.Cell,
 			Alias:     fmt.Sprintf("%s-%010d", cluster.Cell, tabletUID),
 		}
 		if i == 0 { // Make the first one as primary