bump to 500 pool size

Signed-off-by: Olga Shestopalova <oshestopalova@hubspot.com>

go/flags/endtoend/vtgate.txt

@@ -230,7 +230,7 @@ Flags:
       --vschema_ddl_authorized_users string                              List of users authorized to execute vschema ddl operations, or '%' to allow all users.
       --vtgate-config-terse-errors                                       prevent bind vars from escaping in returned errors
       --warming-reads-percent int                                        Percentage of reads on the primary to forward to replicas. Useful for keeping buffer pools warm. (default 0)
-      --warming-reads-pool-size int                                      Size of goroutine pool for warming reads (default 100)
+      --warming-reads-pool-size int                                      Size of goroutine pool for warming reads (default 500)
       --warming-reads-query-timeout duration                             Timeout of warming read queries (default 5s)
       --warn_memory_rows int                                             Warning threshold for in-memory results. A row count higher than this amount will cause the VtGateWarnings.ResultsExceeded counter to be incremented. (default 30000)
       --warn_payload_size int                                            The warning threshold for query payloads in bytes. A payload greater than this threshold will cause the VtGateWarnings.WarnPayloadSizeExceeded counter to be incremented.

go/vt/vtgate/engine/route.go

@@ -628,5 +628,6 @@ func (route *Route) executeWarmingReplicaRead(ctx context.Context, vcursor VCurs
 			}
 		}(replicaVCursor)
 	default:
+		log.Warning("Failed to execute warming replica read as pool is full")
 	}
 }

go/vt/vtgate/vtgate.go

@@ -114,7 +114,7 @@ var (
 
 	warmingReadsPercent      = 0
 	warmingReadsQueryTimeout = 5 * time.Second
-	warmingReadsPoolSize     = 100
+	warmingReadsPoolSize     = 500
 )
 
 func registerFlags(fs *pflag.FlagSet) {
@@ -149,7 +149,7 @@ func registerFlags(fs *pflag.FlagSet) {
 	fs.BoolVar(&enableViews, "enable-views", enableViews, "Enable views support in vtgate.")
 	fs.BoolVar(&allowKillStmt, "allow-kill-statement", allowKillStmt, "Allows the execution of kill statement")
 	fs.IntVar(&warmingReadsPercent, "warming-reads-percent", 0, "Percentage of reads on the primary to forward to replicas. Useful for keeping buffer pools warm (default 0)")
-	fs.IntVar(&warmingReadsPoolSize, "warming-reads-pool-size", 100, "Size of goroutine pool for warming reads (default 100)")
+	fs.IntVar(&warmingReadsPoolSize, "warming-reads-pool-size", 500, "Size of goroutine pool for warming reads (default 500)")
 	fs.DurationVar(&warmingReadsQueryTimeout, "warming-reads-query-timeout", 5*time.Second, "Timeout of warming read queries (default 5s)")
 
 	_ = fs.String("schema_change_signal_user", "", "User to be used to send down query to vttablet to retrieve schema changes")