// Copyright (c) 2012 The gocql Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gocql
//This file will be the future home for more policies
import (
"context"
"errors"
"fmt"
"math"
"math/rand"
"net"
"sync"
"sync/atomic"
"time"
"github.com/hailocab/go-hostpool"
)
// cowHostList implements a copy on write host list, its equivalent type is []*HostInfo
type cowHostList struct {
list atomic.Value
mu sync.Mutex
}
func (c *cowHostList) String() string {
return fmt.Sprintf("%+v", c.get())
}
func (c *cowHostList) get() []*HostInfo {
// TODO(zariel): should we replace this with []*HostInfo?
l, ok := c.list.Load().(*[]*HostInfo)
if !ok {
return nil
}
return *l
}
// add will add a host if it not already in the list
func (c *cowHostList) add(host *HostInfo) bool {
c.mu.Lock()
l := c.get()
if n := len(l); n == 0 {
l = []*HostInfo{host}
} else {
newL := make([]*HostInfo, n+1)
for i := 0; i < n; i++ {
if host.Equal(l[i]) {
c.mu.Unlock()
return false
}
newL[i] = l[i]
}
newL[n] = host
l = newL
}
c.list.Store(&l)
c.mu.Unlock()
return true
}
func (c *cowHostList) remove(ip net.IP) bool {
c.mu.Lock()
l := c.get()
size := len(l)
if size == 0 {
c.mu.Unlock()
return false
}
found := false
newL := make([]*HostInfo, 0, size)
for i := 0; i < len(l); i++ {
if !l[i].ConnectAddress().Equal(ip) {
newL = append(newL, l[i])
} else {
found = true
}
}
if !found {
c.mu.Unlock()
return false
}
newL = newL[: size-1 : size-1]
c.list.Store(&newL)
c.mu.Unlock()
return true
}
// RetryableQuery is an interface that represents a query or batch statement that
// exposes the correct functions for the retry policy logic to evaluate correctly.
type RetryableQuery interface {
Attempts() int
SetConsistency(c Consistency)
GetConsistency() Consistency
Context() context.Context
}
type RetryType uint16
const (
Retry RetryType = 0x00 // retry on same connection
RetryNextHost RetryType = 0x01 // retry on another connection
Ignore RetryType = 0x02 // ignore error and return result
Rethrow RetryType = 0x03 // raise error and stop retrying
)
// ErrUnknownRetryType is returned if the retry policy returns a retry type
// unknown to the query executor.
var ErrUnknownRetryType = errors.New("unknown retry type returned by retry policy")
// RetryPolicy interface is used by gocql to determine if a query can be attempted
// again after a retryable error has been received. The interface allows gocql
// users to implement their own logic to determine if a query can be attempted
// again.
//
// See SimpleRetryPolicy as an example of implementing and using a RetryPolicy
// interface.
type RetryPolicy interface {
Attempt(RetryableQuery) bool
GetRetryType(error) RetryType
}
// SimpleRetryPolicy has simple logic for attempting a query a fixed number of times.
//
// See below for examples of usage:
//
// //Assign to the cluster
// cluster.RetryPolicy = &gocql.SimpleRetryPolicy{NumRetries: 3}
//
// //Assign to a query
// query.RetryPolicy(&gocql.SimpleRetryPolicy{NumRetries: 1})
type SimpleRetryPolicy struct {
NumRetries int //Number of times to retry a query
}
// Attempt tells gocql to attempt the query again based on query.Attempts being less
// than the NumRetries defined in the policy.
func (s *SimpleRetryPolicy) Attempt(q RetryableQuery) bool {
return q.Attempts() <= s.NumRetries
}
func (s *SimpleRetryPolicy) GetRetryType(err error) RetryType {
return RetryNextHost
}
// ExponentialBackoffRetryPolicy sleeps between attempts
type ExponentialBackoffRetryPolicy struct {
NumRetries int
Min, Max time.Duration
}
func (e *ExponentialBackoffRetryPolicy) Attempt(q RetryableQuery) bool {
if q.Attempts() > e.NumRetries {
return false
}
time.Sleep(e.napTime(q.Attempts()))
return true
}
// used to calculate exponentially growing time
func getExponentialTime(min time.Duration, max time.Duration, attempts int) time.Duration {
if min <= 0 {
min = 100 * time.Millisecond
}
if max <= 0 {
max = 10 * time.Second
}
minFloat := float64(min)
napDuration := minFloat * math.Pow(2, float64(attempts-1))
// add some jitter
napDuration += rand.Float64()*minFloat - (minFloat / 2)
if napDuration > float64(max) {
return time.Duration(max)
}
return time.Duration(napDuration)
}
func (e *ExponentialBackoffRetryPolicy) GetRetryType(err error) RetryType {
return RetryNextHost
}
// DowngradingConsistencyRetryPolicy: Next retry will be with the next consistency level
// provided in the slice
//
// On a read timeout: the operation is retried with the next provided consistency
// level.
//
// On a write timeout: if the operation is an :attr:`~.UNLOGGED_BATCH`
// and at least one replica acknowledged the write, the operation is
// retried with the next consistency level. Furthermore, for other
// write types, if at least one replica acknowledged the write, the
// timeout is ignored.
//
// On an unavailable exception: if at least one replica is alive, the
// operation is retried with the next provided consistency level.
type DowngradingConsistencyRetryPolicy struct {
ConsistencyLevelsToTry []Consistency
}
func (d *DowngradingConsistencyRetryPolicy) Attempt(q RetryableQuery) bool {
currentAttempt := q.Attempts()
if currentAttempt > len(d.ConsistencyLevelsToTry) {
return false
} else if currentAttempt > 0 {
q.SetConsistency(d.ConsistencyLevelsToTry[currentAttempt-1])
}
return true
}
func (d *DowngradingConsistencyRetryPolicy) GetRetryType(err error) RetryType {
switch t := err.(type) {
case *RequestErrUnavailable:
if t.Alive > 0 {
return Retry
}
return Rethrow
case *RequestErrWriteTimeout:
if t.WriteType == "SIMPLE" || t.WriteType == "BATCH" || t.WriteType == "COUNTER" {
if t.Received > 0 {
return Ignore
}
return Rethrow
}
if t.WriteType == "UNLOGGED_BATCH" {
return Retry
}
return Rethrow
case *RequestErrReadTimeout:
return Retry
default:
return RetryNextHost
}
}
func (e *ExponentialBackoffRetryPolicy) napTime(attempts int) time.Duration {
return getExponentialTime(e.Min, e.Max, attempts)
}
type HostStateNotifier interface {
AddHost(host *HostInfo)
RemoveHost(host *HostInfo)
HostUp(host *HostInfo)
HostDown(host *HostInfo)
}
type KeyspaceUpdateEvent struct {
Keyspace string
Change string
}
type HostTierer interface {
// HostTier returns an integer specifying how far a host is from the client.
// Tier must start at 0.
// The value is used to prioritize closer hosts during host selection.
// For example this could be:
// 0 - local rack, 1 - local DC, 2 - remote DC
// or:
// 0 - local DC, 1 - remote DC
HostTier(host *HostInfo) uint
// This function returns the maximum possible host tier
MaxHostTier() uint
}
// HostSelectionPolicy is an interface for selecting
// the most appropriate host to execute a given query.
// HostSelectionPolicy instances cannot be shared between sessions.
type HostSelectionPolicy interface {
HostStateNotifier
SetPartitioner
KeyspaceChanged(KeyspaceUpdateEvent)
Init(*Session)
IsLocal(host *HostInfo) bool
// Pick returns an iteration function over selected hosts.
// Multiple attempts of a single query execution won't call the returned NextHost function concurrently,
// so it's safe to have internal state without additional synchronization as long as every call to Pick returns
// a different instance of NextHost.
Pick(ExecutableQuery) NextHost
}
// SelectedHost is an interface returned when picking a host from a host
// selection policy.
type SelectedHost interface {
Info() *HostInfo
Mark(error)
}
type selectedHost HostInfo
func (host *selectedHost) Info() *HostInfo {
return (*HostInfo)(host)
}
func (host *selectedHost) Mark(err error) {}
// NextHost is an iteration function over picked hosts
type NextHost func() SelectedHost
// RoundRobinHostPolicy is a round-robin load balancing policy, where each host
// is tried sequentially for each query.
func RoundRobinHostPolicy() HostSelectionPolicy {
return &roundRobinHostPolicy{}
}
type roundRobinHostPolicy struct {
hosts cowHostList
lastUsedHostIdx uint64
}
func (r *roundRobinHostPolicy) IsLocal(*HostInfo) bool { return true }
func (r *roundRobinHostPolicy) KeyspaceChanged(KeyspaceUpdateEvent) {}
func (r *roundRobinHostPolicy) SetPartitioner(partitioner string) {}
func (r *roundRobinHostPolicy) Init(*Session) {}
func (r *roundRobinHostPolicy) Pick(qry ExecutableQuery) NextHost {
nextStartOffset := atomic.AddUint64(&r.lastUsedHostIdx, 1)
return roundRobbin(int(nextStartOffset), r.hosts.get())
}
func (r *roundRobinHostPolicy) AddHost(host *HostInfo) {
r.hosts.add(host)
}
func (r *roundRobinHostPolicy) RemoveHost(host *HostInfo) {
r.hosts.remove(host.ConnectAddress())
}
func (r *roundRobinHostPolicy) HostUp(host *HostInfo) {
r.AddHost(host)
}
func (r *roundRobinHostPolicy) HostDown(host *HostInfo) {
r.RemoveHost(host)
}
func ShuffleReplicas() func(*tokenAwareHostPolicy) {
return func(t *tokenAwareHostPolicy) {
t.shuffleReplicas = true
}
}
// NonLocalReplicasFallback enables fallback to replicas that are not considered local.
//
// TokenAwareHostPolicy used with DCAwareHostPolicy fallback first selects replicas by partition key in local DC, then
// falls back to other nodes in the local DC. Enabling NonLocalReplicasFallback causes TokenAwareHostPolicy
// to first select replicas by partition key in local DC, then replicas by partition key in remote DCs and fall back
// to other nodes in local DC.
func NonLocalReplicasFallback() func(policy *tokenAwareHostPolicy) {
return func(t *tokenAwareHostPolicy) {
t.nonLocalReplicasFallback = true
}
}
// TokenAwareHostPolicy is a token aware host selection policy, where hosts are
// selected based on the partition key, so queries are sent to the host which
// owns the partition. Fallback is used when routing information is not available.
func TokenAwareHostPolicy(fallback HostSelectionPolicy, opts ...func(*tokenAwareHostPolicy)) HostSelectionPolicy {
p := &tokenAwareHostPolicy{fallback: fallback}
for _, opt := range opts {
opt(p)
}
return p
}
// clusterMeta holds metadata about cluster topology.
// It is used inside atomic.Value and shallow copies are used when replacing it,
// so fields should not be modified in-place. Instead, to modify a field a copy of the field should be made
// and the pointer in clusterMeta updated to point to the new value.
type clusterMeta struct {
// replicas is map[keyspace]map[token]hosts
replicas map[string]tokenRingReplicas
tokenRing *tokenRing
}
type tokenAwareHostPolicy struct {
fallback HostSelectionPolicy
getKeyspaceMetadata func(keyspace string) (*KeyspaceMetadata, error)
getKeyspaceName func() string
shuffleReplicas bool
nonLocalReplicasFallback bool
// mu protects writes to hosts, partitioner, metadata.
// reads can be unlocked as long as they are not used for updating state later.
mu sync.Mutex
hosts cowHostList
partitioner string
metadata atomic.Value // *clusterMeta
logger StdLogger
}
func (t *tokenAwareHostPolicy) Init(s *Session) {
t.mu.Lock()
defer t.mu.Unlock()
if t.getKeyspaceMetadata != nil {
// Init was already called.
// See https://github.com/scylladb/gocql/issues/94.
panic("sharing token aware host selection policy between sessions is not supported")
}
t.getKeyspaceMetadata = s.KeyspaceMetadata
t.getKeyspaceName = func() string { return s.cfg.Keyspace }
t.logger = s.logger
}
func (t *tokenAwareHostPolicy) IsLocal(host *HostInfo) bool {
return t.fallback.IsLocal(host)
}
func (t *tokenAwareHostPolicy) KeyspaceChanged(update KeyspaceUpdateEvent) {
t.mu.Lock()
defer t.mu.Unlock()
meta := t.getMetadataForUpdate()
t.updateReplicas(meta, update.Keyspace)
t.metadata.Store(meta)
}
// updateReplicas updates replicas in clusterMeta.
// It must be called with t.mu mutex locked.
// meta must not be nil and it's replicas field will be updated.
func (t *tokenAwareHostPolicy) updateReplicas(meta *clusterMeta, keyspace string) {
newReplicas := make(map[string]tokenRingReplicas, len(meta.replicas))
ks, err := t.getKeyspaceMetadata(keyspace)
if err == nil {
strat := getStrategy(ks, t.logger)
if strat != nil {
if meta != nil && meta.tokenRing != nil {
newReplicas[keyspace] = strat.replicaMap(meta.tokenRing)
}
}
}
for ks, replicas := range meta.replicas {
if ks != keyspace {
newReplicas[ks] = replicas
}
}
meta.replicas = newReplicas
}
func (t *tokenAwareHostPolicy) SetPartitioner(partitioner string) {
t.mu.Lock()
defer t.mu.Unlock()
if t.partitioner != partitioner {
t.fallback.SetPartitioner(partitioner)
t.partitioner = partitioner
meta := t.getMetadataForUpdate()
meta.resetTokenRing(t.partitioner, t.hosts.get(), t.logger)
t.updateReplicas(meta, t.getKeyspaceName())
t.metadata.Store(meta)
}
}
func (t *tokenAwareHostPolicy) AddHost(host *HostInfo) {
t.mu.Lock()
if t.hosts.add(host) {
meta := t.getMetadataForUpdate()
meta.resetTokenRing(t.partitioner, t.hosts.get(), t.logger)
t.updateReplicas(meta, t.getKeyspaceName())
t.metadata.Store(meta)
}
t.mu.Unlock()
t.fallback.AddHost(host)
}
func (t *tokenAwareHostPolicy) AddHosts(hosts []*HostInfo) {
t.mu.Lock()
for _, host := range hosts {
t.hosts.add(host)
}
meta := t.getMetadataForUpdate()
meta.resetTokenRing(t.partitioner, t.hosts.get(), t.logger)
t.updateReplicas(meta, t.getKeyspaceName())
t.metadata.Store(meta)
t.mu.Unlock()
for _, host := range hosts {
t.fallback.AddHost(host)
}
}
func (t *tokenAwareHostPolicy) RemoveHost(host *HostInfo) {
t.mu.Lock()
if t.hosts.remove(host.ConnectAddress()) {
meta := t.getMetadataForUpdate()
meta.resetTokenRing(t.partitioner, t.hosts.get(), t.logger)
t.updateReplicas(meta, t.getKeyspaceName())
t.metadata.Store(meta)
}
t.mu.Unlock()
t.fallback.RemoveHost(host)
}
func (t *tokenAwareHostPolicy) HostUp(host *HostInfo) {
t.fallback.HostUp(host)
}
func (t *tokenAwareHostPolicy) HostDown(host *HostInfo) {
t.fallback.HostDown(host)
}
// getMetadataReadOnly returns current cluster metadata.
// Metadata uses copy on write, so the returned value should be only used for reading.
// To obtain a copy that could be updated, use getMetadataForUpdate instead.
func (t *tokenAwareHostPolicy) getMetadataReadOnly() *clusterMeta {
meta, _ := t.metadata.Load().(*clusterMeta)
return meta
}
// getMetadataForUpdate returns clusterMeta suitable for updating.
// It is a SHALLOW copy of current metadata in case it was already set or new empty clusterMeta otherwise.
// This function should be called with t.mu mutex locked and the mutex should not be released before
// storing the new metadata.
func (t *tokenAwareHostPolicy) getMetadataForUpdate() *clusterMeta {
metaReadOnly := t.getMetadataReadOnly()
meta := new(clusterMeta)
if metaReadOnly != nil {
*meta = *metaReadOnly
}
return meta
}
// resetTokenRing creates a new tokenRing.
// It must be called with t.mu locked.
func (m *clusterMeta) resetTokenRing(partitioner string, hosts []*HostInfo, logger StdLogger) {
if partitioner == "" {
// partitioner not yet set
return
}
// create a new token ring
tokenRing, err := newTokenRing(partitioner, hosts)
if err != nil {
logger.Printf("Unable to update the token ring due to error: %s", err)
return
}
// replace the token ring
m.tokenRing = tokenRing
}
func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
if qry == nil {
return t.fallback.Pick(qry)
}
routingKey, err := qry.GetRoutingKey()
if err != nil {
return t.fallback.Pick(qry)
} else if routingKey == nil {
return t.fallback.Pick(qry)
}
meta := t.getMetadataReadOnly()
if meta == nil || meta.tokenRing == nil {
return t.fallback.Pick(qry)
}
token := meta.tokenRing.partitioner.Hash(routingKey)
ht := meta.replicas[qry.Keyspace()].replicasFor(token)
var replicas []*HostInfo
if ht == nil {
host, _ := meta.tokenRing.GetHostForToken(token)
replicas = []*HostInfo{host}
} else {
replicas = ht.hosts
if t.shuffleReplicas {
replicas = shuffleHosts(replicas)
}
}
var (
fallbackIter NextHost
i, j, k int
remote [][]*HostInfo
tierer HostTierer
tiererOk bool
maxTier uint
)
if tierer, tiererOk = t.fallback.(HostTierer); tiererOk {
maxTier = tierer.MaxHostTier()
} else {
maxTier = 1
}
if t.nonLocalReplicasFallback {
remote = make([][]*HostInfo, maxTier)
}
used := make(map[*HostInfo]bool, len(replicas))
return func() SelectedHost {
for i < len(replicas) {
h := replicas[i]
i++
var tier uint
if tiererOk {
tier = tierer.HostTier(h)
} else if t.fallback.IsLocal(h) {
tier = 0
} else {
tier = 1
}
if tier != 0 {
if t.nonLocalReplicasFallback {
remote[tier-1] = append(remote[tier-1], h)
}
continue
}
if h.IsUp() {
used[h] = true
return (*selectedHost)(h)
}
}
if t.nonLocalReplicasFallback {
for j < len(remote) && k < len(remote[j]) {
h := remote[j][k]
k++
if k >= len(remote[j]) {
j++
k = 0
}
if h.IsUp() {
used[h] = true
return (*selectedHost)(h)
}
}
}
if fallbackIter == nil {
// fallback
fallbackIter = t.fallback.Pick(qry)
}
// filter the token aware selected hosts from the fallback hosts
for fallbackHost := fallbackIter(); fallbackHost != nil; fallbackHost = fallbackIter() {
if !used[fallbackHost.Info()] {
used[fallbackHost.Info()] = true
return fallbackHost
}
}
return nil
}
}
// HostPoolHostPolicy is a host policy which uses the bitly/go-hostpool library
// to distribute queries between hosts and prevent sending queries to
// unresponsive hosts. When creating the host pool that is passed to the policy
// use an empty slice of hosts as the hostpool will be populated later by gocql.
// See below for examples of usage:
//
// // Create host selection policy using a simple host pool
// cluster.PoolConfig.HostSelectionPolicy = HostPoolHostPolicy(hostpool.New(nil))
//
// // Create host selection policy using an epsilon greedy pool
// cluster.PoolConfig.HostSelectionPolicy = HostPoolHostPolicy(
// hostpool.NewEpsilonGreedy(nil, 0, &hostpool.LinearEpsilonValueCalculator{}),
// )
func HostPoolHostPolicy(hp hostpool.HostPool) HostSelectionPolicy {
return &hostPoolHostPolicy{hostMap: map[string]*HostInfo{}, hp: hp}
}
type hostPoolHostPolicy struct {
hp hostpool.HostPool
mu sync.RWMutex
hostMap map[string]*HostInfo
}
func (r *hostPoolHostPolicy) Init(*Session) {}
func (r *hostPoolHostPolicy) KeyspaceChanged(KeyspaceUpdateEvent) {}
func (r *hostPoolHostPolicy) SetPartitioner(string) {}
func (r *hostPoolHostPolicy) IsLocal(*HostInfo) bool { return true }
func (r *hostPoolHostPolicy) SetHosts(hosts []*HostInfo) {
peers := make([]string, len(hosts))
hostMap := make(map[string]*HostInfo, len(hosts))
for i, host := range hosts {
ip := host.ConnectAddress().String()
peers[i] = ip
hostMap[ip] = host
}
r.mu.Lock()
r.hp.SetHosts(peers)
r.hostMap = hostMap
r.mu.Unlock()
}
func (r *hostPoolHostPolicy) AddHost(host *HostInfo) {
ip := host.ConnectAddress().String()
r.mu.Lock()
defer r.mu.Unlock()
// If the host addr is present and isn't nil return
if h, ok := r.hostMap[ip]; ok && h != nil {
return
}
// otherwise, add the host to the map
r.hostMap[ip] = host
// and construct a new peer list to give to the HostPool
hosts := make([]string, 0, len(r.hostMap))
for addr := range r.hostMap {
hosts = append(hosts, addr)
}
r.hp.SetHosts(hosts)
}
func (r *hostPoolHostPolicy) RemoveHost(host *HostInfo) {
ip := host.ConnectAddress().String()
r.mu.Lock()
defer r.mu.Unlock()
if _, ok := r.hostMap[ip]; !ok {
return
}
delete(r.hostMap, ip)
hosts := make([]string, 0, len(r.hostMap))
for _, host := range r.hostMap {
hosts = append(hosts, host.ConnectAddress().String())
}
r.hp.SetHosts(hosts)
}
func (r *hostPoolHostPolicy) HostUp(host *HostInfo) {
r.AddHost(host)
}
func (r *hostPoolHostPolicy) HostDown(host *HostInfo) {
r.RemoveHost(host)
}
func (r *hostPoolHostPolicy) Pick(qry ExecutableQuery) NextHost {
return func() SelectedHost {
r.mu.RLock()
defer r.mu.RUnlock()
if len(r.hostMap) == 0 {
return nil
}
hostR := r.hp.Get()
host, ok := r.hostMap[hostR.Host()]
if !ok {
return nil
}
return selectedHostPoolHost{
policy: r,
info: host,
hostR: hostR,
}
}
}
// selectedHostPoolHost is a host returned by the hostPoolHostPolicy and
// implements the SelectedHost interface
type selectedHostPoolHost struct {
policy *hostPoolHostPolicy
info *HostInfo
hostR hostpool.HostPoolResponse
}
func (host selectedHostPoolHost) Info() *HostInfo {
return host.info
}
func (host selectedHostPoolHost) Mark(err error) {
ip := host.info.ConnectAddress().String()
host.policy.mu.RLock()
defer host.policy.mu.RUnlock()
if _, ok := host.policy.hostMap[ip]; !ok {
// host was removed between pick and mark
return
}
host.hostR.Mark(err)
}
type dcAwareRR struct {
local string
localHosts cowHostList
remoteHosts cowHostList
lastUsedHostIdx uint64
}
// DCAwareRoundRobinPolicy is a host selection policies which will prioritize and
// return hosts which are in the local datacentre before returning hosts in all
// other datercentres
func DCAwareRoundRobinPolicy(localDC string) HostSelectionPolicy {
return &dcAwareRR{local: localDC}
}
func (d *dcAwareRR) Init(*Session) {}
func (d *dcAwareRR) KeyspaceChanged(KeyspaceUpdateEvent) {}
func (d *dcAwareRR) SetPartitioner(p string) {}
func (d *dcAwareRR) IsLocal(host *HostInfo) bool {
return host.DataCenter() == d.local
}
func (d *dcAwareRR) AddHost(host *HostInfo) {
if d.IsLocal(host) {
d.localHosts.add(host)
} else {
d.remoteHosts.add(host)
}
}
func (d *dcAwareRR) RemoveHost(host *HostInfo) {
if d.IsLocal(host) {
d.localHosts.remove(host.ConnectAddress())
} else {
d.remoteHosts.remove(host.ConnectAddress())
}
}
func (d *dcAwareRR) HostUp(host *HostInfo) { d.AddHost(host) }
func (d *dcAwareRR) HostDown(host *HostInfo) { d.RemoveHost(host) }
// This function is supposed to be called in a fashion
// roundRobbin(offset, hostsPriority1, hostsPriority2, hostsPriority3 ... )
//
// E.g. for DC-naive strategy:
// roundRobbin(offset, allHosts)
//
// For tiered and DC-aware strategy:
// roundRobbin(offset, localHosts, remoteHosts)
func roundRobbin(shift int, hosts ...[]*HostInfo) NextHost {
currentLayer := 0
currentlyObserved := 0
return func() SelectedHost {
// iterate over layers
for {
if currentLayer == len(hosts) {
return nil
}
currentLayerSize := len(hosts[currentLayer])
// iterate over hosts within a layer
for {
currentlyObserved++
if currentlyObserved > currentLayerSize {
currentLayer++
currentlyObserved = 0
break
}
h := hosts[currentLayer][(shift+currentlyObserved)%currentLayerSize]
if h.IsUp() {
return (*selectedHost)(h)
}
}
}
}
}
func (d *dcAwareRR) Pick(q ExecutableQuery) NextHost {
nextStartOffset := atomic.AddUint64(&d.lastUsedHostIdx, 1)
return roundRobbin(int(nextStartOffset), d.localHosts.get(), d.remoteHosts.get())
}
// RackAwareRoundRobinPolicy is a host selection policies which will prioritize and
// return hosts which are in the local rack, before hosts in the local datacenter but
// a different rack, before hosts in all other datercentres
type rackAwareRR struct {
// lastUsedHostIdx keeps the index of the last used host.
// It is accessed atomically and needs to be aligned to 64 bits, so we
// keep it first in the struct. Do not move it or add new struct members
// before it.
lastUsedHostIdx uint64
localDC string
localRack string
hosts []cowHostList
}
func RackAwareRoundRobinPolicy(localDC string, localRack string) HostSelectionPolicy {
hosts := make([]cowHostList, 3)
return &rackAwareRR{localDC: localDC, localRack: localRack, hosts: hosts}
}
func (d *rackAwareRR) Init(*Session) {}
func (d *rackAwareRR) KeyspaceChanged(KeyspaceUpdateEvent) {}
func (d *rackAwareRR) SetPartitioner(p string) {}
func (d *rackAwareRR) MaxHostTier() uint {
return 2
}
func (d *rackAwareRR) HostTier(host *HostInfo) uint {
if host.DataCenter() == d.localDC {
if host.Rack() == d.localRack {
return 0
} else {
return 1
}
} else {
return 2
}
}
func (d *rackAwareRR) IsLocal(host *HostInfo) bool {
return d.HostTier(host) == 0
}
func (d *rackAwareRR) AddHost(host *HostInfo) {
dist := d.HostTier(host)
d.hosts[dist].add(host)
}
func (d *rackAwareRR) RemoveHost(host *HostInfo) {
dist := d.HostTier(host)
d.hosts[dist].remove(host.ConnectAddress())
}
func (d *rackAwareRR) HostUp(host *HostInfo) { d.AddHost(host) }
func (d *rackAwareRR) HostDown(host *HostInfo) { d.RemoveHost(host) }
func (d *rackAwareRR) Pick(q ExecutableQuery) NextHost {
nextStartOffset := atomic.AddUint64(&d.lastUsedHostIdx, 1)
return roundRobbin(int(nextStartOffset), d.hosts[0].get(), d.hosts[1].get(), d.hosts[2].get())
}
// ReadyPolicy defines a policy for when a HostSelectionPolicy can be used. After
// each host connects during session initialization, the Ready method will be
// called. If you only need a single Host to be up you can wrap a
// HostSelectionPolicy policy with SingleHostReadyPolicy.
type ReadyPolicy interface {
Ready() bool
}
// SingleHostReadyPolicy wraps a HostSelectionPolicy and returns Ready after a
// single host has been added via HostUp
func SingleHostReadyPolicy(p HostSelectionPolicy) *singleHostReadyPolicy {
return &singleHostReadyPolicy{
HostSelectionPolicy: p,
}
}
type singleHostReadyPolicy struct {
HostSelectionPolicy
ready bool
readyMux sync.Mutex
}
func (s *singleHostReadyPolicy) HostUp(host *HostInfo) {
s.HostSelectionPolicy.HostUp(host)
s.readyMux.Lock()
s.ready = true
s.readyMux.Unlock()
}
func (s *singleHostReadyPolicy) Ready() bool {
s.readyMux.Lock()
ready := s.ready
s.readyMux.Unlock()
if !ready {
return false
}
// in case the wrapped policy is also a ReadyPolicy, defer to that
if rdy, ok := s.HostSelectionPolicy.(ReadyPolicy); ok {
return rdy.Ready()
}
return true
}
// ConvictionPolicy interface is used by gocql to determine if a host should be
// marked as DOWN based on the error and host info
type ConvictionPolicy interface {
// Implementations should return `true` if the host should be convicted, `false` otherwise.
AddFailure(error error, host *HostInfo) bool
//Implementations should clear out any convictions or state regarding the host.
Reset(host *HostInfo)
}
// SimpleConvictionPolicy implements a ConvictionPolicy which convicts all hosts
// regardless of error
type SimpleConvictionPolicy struct {
}
func (e *SimpleConvictionPolicy) AddFailure(error error, host *HostInfo) bool {
return true
}
func (e *SimpleConvictionPolicy) Reset(host *HostInfo) {}
// ReconnectionPolicy interface is used by gocql to determine if reconnection
// can be attempted after connection error. The interface allows gocql users
// to implement their own logic to determine how to attempt reconnection.
type ReconnectionPolicy interface {
GetInterval(currentRetry int) time.Duration
GetMaxRetries() int
}
// ConstantReconnectionPolicy has simple logic for returning a fixed reconnection interval.
//
// Examples of usage:
//
// cluster.ReconnectionPolicy = &gocql.ConstantReconnectionPolicy{MaxRetries: 10, Interval: 8 * time.Second}
type ConstantReconnectionPolicy struct {
MaxRetries int
Interval time.Duration
}
func (c *ConstantReconnectionPolicy) GetInterval(currentRetry int) time.Duration {
return c.Interval
}
func (c *ConstantReconnectionPolicy) GetMaxRetries() int {
return c.MaxRetries
}
// ExponentialReconnectionPolicy returns a growing reconnection interval.
type ExponentialReconnectionPolicy struct {
MaxRetries int
InitialInterval time.Duration
MaxInterval time.Duration
}
func (e *ExponentialReconnectionPolicy) GetInterval(currentRetry int) time.Duration {
max := e.MaxInterval
if max < e.InitialInterval {
max = math.MaxInt16 * time.Second
}
return getExponentialTime(e.InitialInterval, max, currentRetry)
}
func (e *ExponentialReconnectionPolicy) GetMaxRetries() int {
return e.MaxRetries
}
type SpeculativeExecutionPolicy interface {
Attempts() int
Delay() time.Duration
}
type NonSpeculativeExecution struct{}
func (sp NonSpeculativeExecution) Attempts() int { return 0 } // No additional attempts
func (sp NonSpeculativeExecution) Delay() time.Duration { return 1 } // The delay. Must be positive to be used in a ticker.
type SimpleSpeculativeExecution struct {
NumAttempts int
TimeoutDelay time.Duration
}
func (sp *SimpleSpeculativeExecution) Attempts() int { return sp.NumAttempts }
func (sp *SimpleSpeculativeExecution) Delay() time.Duration { return sp.TimeoutDelay }