host_source.go

package gocql

import (
	"context"
	"errors"
	"fmt"
	"net"
	"strconv"
	"strings"
	"sync"
	"time"
)

var ErrCannotFindHost = errors.New("cannot find host")
var ErrHostAlreadyExists = errors.New("host already exists")

type nodeState int32

func (n nodeState) String() string {
	if n == NodeUp {
		return "UP"
	} else if n == NodeDown {
		return "DOWN"
	}
	return fmt.Sprintf("UNKNOWN_%d", n)
}

const (
	NodeUp nodeState = iota
	NodeDown
)

type cassVersion struct {
	Major, Minor, Patch int
}

func (c *cassVersion) Set(v string) error {
	if v == "" {
		return nil
	}

	return c.UnmarshalCQL(nil, []byte(v))
}

func (c *cassVersion) UnmarshalCQL(info TypeInfo, data []byte) error {
	return c.unmarshal(data)
}

func (c *cassVersion) unmarshal(data []byte) error {
	version := strings.TrimSuffix(string(data), "-SNAPSHOT")
	version = strings.TrimPrefix(version, "v")
	v := strings.Split(version, ".")

	if len(v) < 2 {
		return fmt.Errorf("invalid version string: %s", data)
	}

	var err error
	c.Major, err = strconv.Atoi(v[0])
	if err != nil {
		return fmt.Errorf("invalid major version %v: %v", v[0], err)
	}

	c.Minor, err = strconv.Atoi(v[1])
	if err != nil {
		return fmt.Errorf("invalid minor version %v: %v", v[1], err)
	}

	if len(v) > 2 {
		c.Patch, err = strconv.Atoi(v[2])
		if err != nil {
			return fmt.Errorf("invalid patch version %v: %v", v[2], err)
		}
	}

	return nil
}

func (c cassVersion) Before(major, minor, patch int) bool {
	// We're comparing us (cassVersion) with the provided version (major, minor, patch)
	// We return true if our version is lower (comes before) than the provided one.
	if c.Major < major {
		return true
	} else if c.Major == major {
		if c.Minor < minor {
			return true
		} else if c.Minor == minor && c.Patch < patch {
			return true
		}

	}
	return false
}

func (c cassVersion) AtLeast(major, minor, patch int) bool {
	return !c.Before(major, minor, patch)
}

func (c cassVersion) String() string {
	return fmt.Sprintf("v%d.%d.%d", c.Major, c.Minor, c.Patch)
}

func (c cassVersion) nodeUpDelay() time.Duration {
	if c.Major >= 2 && c.Minor >= 2 {
		// CASSANDRA-8236
		return 0
	}

	return 10 * time.Second
}

type HostInfo struct {
	// TODO(zariel): reduce locking maybe, not all values will change, but to ensure
	// that we are thread safe use a mutex to access all fields.
	mu                         sync.RWMutex
	hostname                   string
	peer                       net.IP
	broadcastAddress           net.IP
	listenAddress              net.IP
	rpcAddress                 net.IP
	preferredIP                net.IP
	connectAddress             net.IP
	untranslatedConnectAddress net.IP
	port                       int
	dataCenter                 string
	rack                       string
	hostId                     string
	workload                   string
	graph                      bool
	dseVersion                 string
	partitioner                string
	clusterName                string
	version                    cassVersion
	state                      nodeState
	schemaVersion              string
	tokens                     []string

	scyllaShardAwarePort    uint16
	scyllaShardAwarePortTLS uint16
}

func (h *HostInfo) Equal(host *HostInfo) bool {
	if h == host {
		// prevent rlock reentry
		return true
	}

	return h.HostID() == host.HostID() && h.ConnectAddressAndPort() == host.ConnectAddressAndPort()
}

func (h *HostInfo) Peer() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.peer
}

func (h *HostInfo) invalidConnectAddr() bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	addr, _ := h.connectAddressLocked()
	return !validIpAddr(addr)
}

func validIpAddr(addr net.IP) bool {
	return addr != nil && !addr.IsUnspecified()
}

func (h *HostInfo) connectAddressLocked() (net.IP, string) {
	if validIpAddr(h.connectAddress) {
		return h.connectAddress, "connect_address"
	} else if validIpAddr(h.rpcAddress) {
		return h.rpcAddress, "rpc_adress"
	} else if validIpAddr(h.preferredIP) {
		// where does perferred_ip get set?
		return h.preferredIP, "preferred_ip"
	} else if validIpAddr(h.broadcastAddress) {
		return h.broadcastAddress, "broadcast_address"
	} else if validIpAddr(h.peer) {
		return h.peer, "peer"
	}
	return net.IPv4zero, "invalid"
}

// nodeToNodeAddress returns address broadcasted between node to nodes.
// It's either `broadcast_address` if host info is read from system.local or `peer` if read from system.peers.
// This IP address is also part of CQL Event emitted on topology/status changes,
// but does not uniquely identify the node in case multiple nodes use the same IP address.
func (h *HostInfo) nodeToNodeAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()

	if validIpAddr(h.broadcastAddress) {
		return h.broadcastAddress
	} else if validIpAddr(h.peer) {
		return h.peer
	}
	return net.IPv4zero
}

// Returns the address that should be used to connect to the host.
// If you wish to override this, use an AddressTranslator or
// use a HostFilter to SetConnectAddress()
func (h *HostInfo) ConnectAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()

	if addr, _ := h.connectAddressLocked(); validIpAddr(addr) {
		return addr
	}
	panic(fmt.Sprintf("no valid connect address for host: %v. Is your cluster configured correctly?", h))
}

func (h *HostInfo) UntranslatedConnectAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()

	if len(h.untranslatedConnectAddress) != 0 {
		return h.untranslatedConnectAddress
	}

	if addr, _ := h.connectAddressLocked(); validIpAddr(addr) {
		return addr
	}
	panic(fmt.Sprintf("no valid connect address for host: %v. Is your cluster configured correctly?", h))
}

func (h *HostInfo) SetConnectAddress(address net.IP) *HostInfo {
	// TODO(zariel): should this not be exported?
	h.mu.Lock()
	defer h.mu.Unlock()
	h.connectAddress = address
	return h
}

func (h *HostInfo) BroadcastAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.broadcastAddress
}

func (h *HostInfo) ListenAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.listenAddress
}

func (h *HostInfo) RPCAddress() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.rpcAddress
}

func (h *HostInfo) PreferredIP() net.IP {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.preferredIP
}

func (h *HostInfo) DataCenter() string {
	h.mu.RLock()
	dc := h.dataCenter
	h.mu.RUnlock()
	return dc
}

func (h *HostInfo) Rack() string {
	h.mu.RLock()
	rack := h.rack
	h.mu.RUnlock()
	return rack
}

func (h *HostInfo) HostID() string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.hostId
}

func (h *HostInfo) SetHostID(hostID string) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.hostId = hostID
}

func (h *HostInfo) WorkLoad() string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.workload
}

func (h *HostInfo) Graph() bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.graph
}

func (h *HostInfo) DSEVersion() string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.dseVersion
}

func (h *HostInfo) Partitioner() string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.partitioner
}

func (h *HostInfo) ClusterName() string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.clusterName
}

func (h *HostInfo) Version() cassVersion {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.version
}

func (h *HostInfo) State() nodeState {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.state
}

func (h *HostInfo) setState(state nodeState) *HostInfo {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.state = state
	return h
}

func (h *HostInfo) Tokens() []string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.tokens
}

func (h *HostInfo) Port() int {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.port
}

func (h *HostInfo) update(from *HostInfo) {
	if h == from {
		return
	}

	h.mu.Lock()
	defer h.mu.Unlock()

	from.mu.RLock()
	defer from.mu.RUnlock()

	// autogenerated do not update
	if h.peer == nil {
		h.peer = from.peer
	}
	if h.broadcastAddress == nil {
		h.broadcastAddress = from.broadcastAddress
	}
	if h.listenAddress == nil {
		h.listenAddress = from.listenAddress
	}
	if h.rpcAddress == nil {
		h.rpcAddress = from.rpcAddress
	}
	if h.preferredIP == nil {
		h.preferredIP = from.preferredIP
	}
	if h.connectAddress == nil {
		h.connectAddress = from.connectAddress
	}
	if h.port == 0 {
		h.port = from.port
	}
	if h.dataCenter == "" {
		h.dataCenter = from.dataCenter
	}
	if h.rack == "" {
		h.rack = from.rack
	}
	if h.hostId == "" {
		h.hostId = from.hostId
	}
	if h.workload == "" {
		h.workload = from.workload
	}
	if h.dseVersion == "" {
		h.dseVersion = from.dseVersion
	}
	if h.partitioner == "" {
		h.partitioner = from.partitioner
	}
	if h.clusterName == "" {
		h.clusterName = from.clusterName
	}
	if h.version == (cassVersion{}) {
		h.version = from.version
	}
	if h.tokens == nil {
		h.tokens = from.tokens
	}
}

func (h *HostInfo) IsUp() bool {
	return h != nil && h.State() == NodeUp
}

func (h *HostInfo) IsBusy(s *Session) bool {
	pool, ok := s.pool.getPool(h)
	return ok && h != nil && pool.InFlight() >= MAX_IN_FLIGHT_THRESHOLD
}

func (h *HostInfo) HostnameAndPort() string {
	// Fast path: in most cases hostname is not empty
	var (
		hostname string
		port     int
	)
	h.mu.RLock()
	hostname = h.hostname
	port = h.port
	h.mu.RUnlock()

	if hostname != "" {
		return net.JoinHostPort(hostname, strconv.Itoa(port))
	}

	// Slow path: hostname is empty
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.hostname == "" { // recheck is hostname empty
		// if yes - fill it
		addr, _ := h.connectAddressLocked()
		h.hostname = addr.String()
	}
	return net.JoinHostPort(h.hostname, strconv.Itoa(h.port))
}

func (h *HostInfo) Hostname() string {
	// Fast path: in most cases hostname is not empty
	var hostname string
	h.mu.RLock()
	hostname = h.hostname
	h.mu.RUnlock()

	if hostname != "" {
		return hostname
	}

	// Slow path: hostname is empty
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.hostname == "" {
		addr, _ := h.connectAddressLocked()
		h.hostname = addr.String()
	}
	return h.hostname
}

func (h *HostInfo) ConnectAddressAndPort() string {
	h.mu.Lock()
	defer h.mu.Unlock()
	addr, _ := h.connectAddressLocked()
	return net.JoinHostPort(addr.String(), strconv.Itoa(h.port))
}

func (h *HostInfo) String() string {
	h.mu.RLock()
	defer h.mu.RUnlock()

	connectAddr, source := h.connectAddressLocked()
	return fmt.Sprintf("[HostInfo hostname=%q connectAddress=%q peer=%q rpc_address=%q broadcast_address=%q "+
		"preferred_ip=%q connect_addr=%q connect_addr_source=%q "+
		"port=%d data_centre=%q rack=%q host_id=%q version=%q state=%s num_tokens=%d]",
		h.hostname, h.connectAddress, h.peer, h.rpcAddress, h.broadcastAddress, h.preferredIP,
		connectAddr, source,
		h.port, h.dataCenter, h.rack, h.hostId, h.version, h.state, len(h.tokens))
}

func (h *HostInfo) setScyllaSupported(s scyllaSupported) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.scyllaShardAwarePort = s.shardAwarePort
	h.scyllaShardAwarePortTLS = s.shardAwarePortSSL
}

// ScyllaShardAwarePort returns the shard aware port of this host.
// Returns zero if the shard aware port is not known.
func (h *HostInfo) ScyllaShardAwarePort() uint16 {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.scyllaShardAwarePort
}

// ScyllaShardAwarePortTLS returns the TLS-enabled shard aware port of this host.
// Returns zero if the shard aware port is not known.
func (h *HostInfo) ScyllaShardAwarePortTLS() uint16 {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.scyllaShardAwarePortTLS
}

// Experimental, this interface and use may change
type ReplicaInfo struct {
	hostId  UUID
	shardId int
}

// Experimental, this interface and use may change
type TabletInfo struct {
	keyspaceName string
	tableName    string
	firstToken   int64
	lastToken    int64
	replicas     []ReplicaInfo
}

func (t *TabletInfo) KeyspaceName() string {
	return t.keyspaceName
}

func (t *TabletInfo) FirstToken() int64 {
	return t.firstToken
}

func (t *TabletInfo) LastToken() int64 {
	return t.lastToken
}

func (t *TabletInfo) TableName() string {
	return t.tableName
}

func (t *TabletInfo) Replicas() []ReplicaInfo {
	return t.replicas
}

// Search for place in tablets table with specific Keyspace and Table name
func findTablets(tablets []*TabletInfo, k string, t string) (int, int) {
	l := -1
	r := -1
	for i, tablet := range tablets {
		if tablet.KeyspaceName() == k && tablet.TableName() == t {
			if l == -1 {
				l = i
			}
			r = i
		} else if l != -1 {
			break
		}
	}

	return l, r
}

func addTabletToTabletsList(tablets []*TabletInfo, tablet *TabletInfo) []*TabletInfo {
	l, r := findTablets(tablets, tablet.keyspaceName, tablet.tableName)
	if l == -1 && r == -1 {
		l = 0
		r = 0
	} else {
		r = r + 1
	}

	l1, r1 := l, r
	l2, r2 := l1, r1

	// find first overlaping range
	for l1 < r1 {
		mid := (l1 + r1) / 2
		if tablets[mid].FirstToken() < tablet.FirstToken() {
			l1 = mid + 1
		} else {
			r1 = mid
		}
	}
	start := l1

	if start > l && tablets[start-1].LastToken() > tablet.FirstToken() {
		start = start - 1
	}

	// find last overlaping range
	for l2 < r2 {
		mid := (l2 + r2) / 2
		if tablets[mid].LastToken() < tablet.LastToken() {
			l2 = mid + 1
		} else {
			r2 = mid
		}
	}
	end := l2
	if end < r && tablets[end].FirstToken() >= tablet.LastToken() {
		end = end - 1
	}
	if end == len(tablets) {
		end = end - 1
	}

	updated_tablets := tablets
	if start <= end {
		// Delete elements from index start to end
		updated_tablets = append(tablets[:start], tablets[end+1:]...)
	}
	// Insert tablet element at index start
	updated_tablets2 := append(updated_tablets[:start], append([]*TabletInfo{tablet}, updated_tablets[start:]...)...)
	return updated_tablets2
}

// Search for place in tablets table for token starting from index l to index r
func findTabletForToken(tablets []*TabletInfo, token Token, l int, r int) *TabletInfo {
	for l < r {
		var m int
		if r*l > 0 {
			m = l + (r-l)/2
		} else {
			m = (r + l) / 2
		}
		if int64Token(tablets[m].LastToken()).Less(token) {
			l = m + 1
		} else {
			r = m
		}
	}

	return tablets[l]
}

// Polls system.peers at a specific interval to find new hosts
type ringDescriber struct {
	session         *Session
	mu              sync.Mutex
	prevHosts       []*HostInfo
	prevPartitioner string
	// Experimental, this interface and use may change
	prevTablets []*TabletInfo
}

// Returns true if we are using system_schema.keyspaces instead of system.schema_keyspaces
func checkSystemSchema(control *controlConn) (bool, error) {
	iter := control.query("SELECT * FROM system_schema.keyspaces" + control.session.usingTimeoutClause)
	if err := iter.err; err != nil {
		if errf, ok := err.(*errorFrame); ok {
			if errf.code == ErrCodeSyntax {
				return false, nil
			}
		}

		return false, err
	}

	return true, nil
}

// Given a map that represents a row from either system.local or system.peers
// return as much information as we can in *HostInfo
func hostInfoFromMap(row map[string]interface{}, host *HostInfo, translateAddressPort func(addr net.IP, port int) (net.IP, int)) (*HostInfo, error) {
	const assertErrorMsg = "Assertion failed for %s"
	var ok bool

	// Default to our connected port if the cluster doesn't have port information
	for key, value := range row {
		switch key {
		case "data_center":
			host.dataCenter, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "data_center")
			}
		case "rack":
			host.rack, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "rack")
			}
		case "host_id":
			hostId, ok := value.(UUID)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "host_id")
			}
			host.hostId = hostId.String()
		case "release_version":
			version, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "release_version")
			}
			host.version.Set(version)
		case "peer":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "peer")
			}
			host.peer = net.ParseIP(ip)
		case "cluster_name":
			host.clusterName, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "cluster_name")
			}
		case "partitioner":
			host.partitioner, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "partitioner")
			}
		case "broadcast_address":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "broadcast_address")
			}
			host.broadcastAddress = net.ParseIP(ip)
		case "preferred_ip":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "preferred_ip")
			}
			host.preferredIP = net.ParseIP(ip)
		case "rpc_address":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "rpc_address")
			}
			host.rpcAddress = net.ParseIP(ip)
		case "native_address":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "native_address")
			}
			host.rpcAddress = net.ParseIP(ip)
		case "listen_address":
			ip, ok := value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "listen_address")
			}
			host.listenAddress = net.ParseIP(ip)
		case "native_port":
			native_port, ok := value.(int)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "native_port")
			}
			host.port = native_port
		case "workload":
			host.workload, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "workload")
			}
		case "graph":
			host.graph, ok = value.(bool)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "graph")
			}
		case "tokens":
			host.tokens, ok = value.([]string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "tokens")
			}
		case "dse_version":
			host.dseVersion, ok = value.(string)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "dse_version")
			}
		case "schema_version":
			schemaVersion, ok := value.(UUID)
			if !ok {
				return nil, fmt.Errorf(assertErrorMsg, "schema_version")
			}
			host.schemaVersion = schemaVersion.String()
		}
		// TODO(thrawn01): Add 'port'? once CASSANDRA-7544 is complete
		// Not sure what the port field will be called until the JIRA issue is complete
	}

	host.untranslatedConnectAddress = host.ConnectAddress()
	ip, port := translateAddressPort(host.untranslatedConnectAddress, host.port)
	host.connectAddress = ip
	host.port = port

	return host, nil
}

func (s *Session) hostInfoFromIter(iter *Iter, connectAddress net.IP, defaultPort int) (*HostInfo, error) {
	rows, err := iter.SliceMap()
	if err != nil {
		// TODO(zariel): make typed error
		return nil, err
	}

	if len(rows) == 0 {
		return nil, errors.New("query returned 0 rows")
	}

	host, err := hostInfoFromMap(rows[0], &HostInfo{connectAddress: connectAddress, port: defaultPort}, s.cfg.translateAddressPort)
	if err != nil {
		return nil, err
	}
	return host, nil
}

// Ask the control node for the local host info
func (r *ringDescriber) getLocalHostInfo() (*HostInfo, error) {
	if r.session.control == nil {
		return nil, errNoControl
	}

	iter := r.session.control.withConnHost(func(ch *connHost) *Iter {
		return ch.conn.querySystemLocal(context.TODO())
	})

	if iter == nil {
		return nil, errNoControl
	}

	host, err := r.session.hostInfoFromIter(iter, nil, r.session.cfg.Port)
	if err != nil {
		return nil, fmt.Errorf("could not retrieve local host info: %w", err)
	}
	return host, nil
}

// Ask the control node for host info on all it's known peers
func (r *ringDescriber) getClusterPeerInfo(localHost *HostInfo) ([]*HostInfo, error) {
	if r.session.control == nil {
		return nil, errNoControl
	}

	var peers []*HostInfo
	iter := r.session.control.withConnHost(func(ch *connHost) *Iter {
		return ch.conn.querySystemPeers(context.TODO(), localHost.version)
	})

	if iter == nil {
		return nil, errNoControl
	}

	rows, err := iter.SliceMap()
	if err != nil {
		// TODO(zariel): make typed error
		return nil, fmt.Errorf("unable to fetch peer host info: %s", err)
	}

	for _, row := range rows {
		// extract all available info about the peer
		host, err := hostInfoFromMap(row, &HostInfo{port: r.session.cfg.Port}, r.session.cfg.translateAddressPort)
		if err != nil {
			return nil, err
		} else if !isValidPeer(host) {
			// If it's not a valid peer
			r.session.logger.Printf("Found invalid peer '%s' "+
				"Likely due to a gossip or snitch issue, this host will be ignored", host)
			continue
		}

		peers = append(peers, host)
	}

	return peers, nil
}

// Return true if the host is a valid peer
func isValidPeer(host *HostInfo) bool {
	return !(len(host.RPCAddress()) == 0 ||
		host.hostId == "" ||
		host.dataCenter == "" ||
		host.rack == "" ||
		len(host.tokens) == 0)
}

// GetHosts returns a list of hosts found via queries to system.local and system.peers
func (r *ringDescriber) GetHosts() ([]*HostInfo, string, error) {
	r.mu.Lock()
	defer r.mu.Unlock()

	localHost, err := r.getLocalHostInfo()
	if err != nil {
		return r.prevHosts, r.prevPartitioner, err
	}

	peerHosts, err := r.getClusterPeerInfo(localHost)
	if err != nil {
		return r.prevHosts, r.prevPartitioner, err
	}

	hosts := append([]*HostInfo{localHost}, peerHosts...)
	var partitioner string
	if len(hosts) > 0 {
		partitioner = hosts[0].Partitioner()
	}

	return hosts, partitioner, nil
}

// Given an ip/port return HostInfo for the specified ip/port
func (r *ringDescriber) getHostInfo(hostID UUID) (*HostInfo, error) {
	var host *HostInfo
	for _, table := range []string{"system.peers", "system.local"} {
		iter := r.session.control.withConnHost(func(ch *connHost) *Iter {
			if ch.host.HostID() == hostID.String() {
				host = ch.host
				return nil
			}

			if table == "system.peers" {
				return ch.conn.querySystemPeers(context.TODO(), ch.host.version)
			} else {
				return ch.conn.query(context.TODO(), fmt.Sprintf("SELECT * FROM %s", table))
			}
		})

		if iter != nil {
			rows, err := iter.SliceMap()
			if err != nil {
				return nil, err
			}

			for _, row := range rows {
				h, err := hostInfoFromMap(row, &HostInfo{port: r.session.cfg.Port}, r.session.cfg.translateAddressPort)
				if err != nil {
					return nil, err
				}

				if h.HostID() == hostID.String() {
					host = h
					break
				}
			}
		}
	}

	if host == nil {
		return nil, errors.New("unable to fetch host info: invalid control connection")
	} else if host.invalidConnectAddr() {
		return nil, fmt.Errorf("host ConnectAddress invalid ip=%v: %v", host.connectAddress, host)
	}

	return host, nil
}

// debounceRingRefresh submits a ring refresh request to the ring refresh debouncer.
func (s *Session) debounceRingRefresh() {
	s.ringRefresher.debounce()
}

// refreshRing executes a ring refresh immediately and cancels pending debounce ring refresh requests.
func (s *Session) refreshRing() error {
	err, ok := <-s.ringRefresher.refreshNow()
	if !ok {
		return errors.New("could not refresh ring because stop was requested")
	}

	return err
}

func refreshRing(r *ringDescriber) error {
	hosts, partitioner, err := r.GetHosts()
	if err != nil {
		return err
	}

	prevHosts := r.session.ring.currentHosts()

	for _, h := range hosts {
		if r.session.cfg.filterHost(h) {
			continue
		}

		if host, ok := r.session.ring.addHostIfMissing(h); !ok {
			r.session.startPoolFill(h)
		} else {
			// host (by hostID) already exists; determine if IP has changed
			newHostID := h.HostID()
			existing, ok := prevHosts[newHostID]
			if !ok {
				return fmt.Errorf("get existing host=%s from prevHosts: %w", h, ErrCannotFindHost)
			}
			if h.connectAddress.Equal(existing.connectAddress) && h.nodeToNodeAddress().Equal(existing.nodeToNodeAddress()) {
				// no host IP change
				host.update(h)
			} else {
				// host IP has changed
				// remove old HostInfo (w/old IP)
				r.session.removeHost(existing)
				if _, alreadyExists := r.session.ring.addHostIfMissing(h); alreadyExists {
					return fmt.Errorf("add new host=%s after removal: %w", h, ErrHostAlreadyExists)
				}
				// add new HostInfo (same hostID, new IP)
				r.session.startPoolFill(h)
			}
		}
		delete(prevHosts, h.HostID())
	}

	for _, host := range prevHosts {
		r.session.removeHost(host)
	}

	r.session.metadata.setPartitioner(partitioner)
	r.session.policy.SetPartitioner(partitioner)

	return nil
}

// Experimental, this interface and use may change
func addTablet(r *ringDescriber, tablet *TabletInfo) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	tablets := r.session.getTablets()
	tablets = addTabletToTabletsList(tablets, tablet)

	r.session.ring.setTablets(tablets)
	r.session.policy.SetTablets(tablets)

	r.session.schemaDescriber.refreshTabletsSchema()

	return nil
}

const (
	ringRefreshDebounceTime = 1 * time.Second
)

// debounces requests to call a refresh function (currently used for ring refresh). It also supports triggering a refresh immediately.
type refreshDebouncer struct {
	mu           sync.Mutex
	stopped      bool
	broadcaster  *errorBroadcaster
	interval     time.Duration
	timer        *time.Timer
	refreshNowCh chan struct{}
	quit         chan struct{}
	refreshFn    func() error
}

func newRefreshDebouncer(interval time.Duration, refreshFn func() error) *refreshDebouncer {
	d := &refreshDebouncer{
		stopped:      false,
		broadcaster:  nil,
		refreshNowCh: make(chan struct{}, 1),
		quit:         make(chan struct{}),
		interval:     interval,
		timer:        time.NewTimer(interval),
		refreshFn:    refreshFn,
	}
	d.timer.Stop()
	go d.flusher()
	return d
}

// debounces a request to call the refresh function
func (d *refreshDebouncer) debounce() {
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.stopped {
		return
	}
	d.timer.Reset(d.interval)
}

// requests an immediate refresh which will cancel pending refresh requests
func (d *refreshDebouncer) refreshNow() <-chan error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.broadcaster == nil {
		d.broadcaster = newErrorBroadcaster()
		select {
		case d.refreshNowCh <- struct{}{}:
		default:
			// already a refresh pending
		}
	}
	return d.broadcaster.newListener()
}

func (d *refreshDebouncer) flusher() {
	for {
		select {
		case <-d.refreshNowCh:
		case <-d.timer.C:
		case <-d.quit:
		}
		d.mu.Lock()
		if d.stopped {
			if d.broadcaster != nil {
				d.broadcaster.stop()
				d.broadcaster = nil
			}
			d.timer.Stop()
			d.mu.Unlock()
			return
		}

		// make sure both request channels are cleared before we refresh
		select {
		case <-d.refreshNowCh:
		default:
		}

		d.timer.Stop()
		select {
		case <-d.timer.C:
		default:
		}

		curBroadcaster := d.broadcaster
		d.broadcaster = nil
		d.mu.Unlock()

		err := d.refreshFn()
		if curBroadcaster != nil {
			curBroadcaster.broadcast(err)
		}
	}
}

func (d *refreshDebouncer) stop() {
	d.mu.Lock()
	if d.stopped {
		d.mu.Unlock()
		return
	}
	d.stopped = true
	d.mu.Unlock()
	d.quit <- struct{}{} // sync with flusher
	close(d.quit)
}

// broadcasts an error to multiple channels (listeners)
type errorBroadcaster struct {
	listeners []chan<- error
	mu        sync.Mutex
}

func newErrorBroadcaster() *errorBroadcaster {
	return &errorBroadcaster{
		listeners: nil,
		mu:        sync.Mutex{},
	}
}

func (b *errorBroadcaster) newListener() <-chan error {
	ch := make(chan error, 1)
	b.mu.Lock()
	defer b.mu.Unlock()
	b.listeners = append(b.listeners, ch)
	return ch
}

func (b *errorBroadcaster) broadcast(err error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	curListeners := b.listeners
	if len(curListeners) > 0 {
		b.listeners = nil
	} else {
		return
	}

	for _, listener := range curListeners {
		listener <- err
		close(listener)
	}
}

func (b *errorBroadcaster) stop() {
	b.mu.Lock()
	defer b.mu.Unlock()
	if len(b.listeners) == 0 {
		return
	}
	for _, listener := range b.listeners {
		close(listener)
	}
	b.listeners = nil
}