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resilient_srv_topo_server.go
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resilient_srv_topo_server.go
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// Copyright 2013, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package vtgate
import (
"flag"
"fmt"
"html/template"
"sort"
"sync"
"time"
log "github.com/golang/glog"
"golang.org/x/net/context"
"github.com/youtube/vitess/go/stats"
"github.com/youtube/vitess/go/vt/topo"
topodatapb "github.com/youtube/vitess/go/vt/proto/topodata"
)
var (
srvTopoCacheTTL = flag.Duration("srv_topo_cache_ttl", 1*time.Second, "how long to use cached entries for topology")
srvTopoTimeout = flag.Duration("srv_topo_timeout", 2*time.Second, "topo server timeout")
)
const (
queryCategory = "query"
cachedCategory = "cached"
errorCategory = "error"
// TopoTemplate is the HTML to use to display the
// ResilientSrvTopoServerCacheStatus object
TopoTemplate = `
<style>
table {
border-collapse: collapse;
}
td, th {
border: 1px solid #999;
padding: 0.2rem;
}
</style>
<table>
<tr>
<th colspan="2">SrvKeyspace Names Cache</th>
</tr>
<tr>
<th>Cell</th>
<th>SrvKeyspace Names</th>
</tr>
{{range $i, $skn := .SrvKeyspaceNames}}
<tr>
<td>{{github_com_youtube_vitess_vtctld_srv_cell $skn.Cell}}</td>
<td>{{if $skn.LastError}}<b>{{$skn.LastError}}</b>{{else}}{{range $j, $value := $skn.Value}}{{github_com_youtube_vitess_vtctld_srv_keyspace $skn.Cell $value}} {{end}}{{end}}</td>
</tr>
{{end}}
</table>
<br>
<table>
<tr>
<th colspan="3">SrvKeyspace Cache</th>
</tr>
<tr>
<th>Cell</th>
<th>Keyspace</th>
<th>SrvKeyspace</th>
</tr>
{{range $i, $sk := .SrvKeyspaces}}
<tr>
<td>{{github_com_youtube_vitess_vtctld_srv_cell $sk.Cell}}</td>
<td>{{github_com_youtube_vitess_vtctld_srv_keyspace $sk.Cell $sk.Keyspace}}</td>
<td>{{if $sk.LastError}}<b>{{$sk.LastError}}</b>{{else}}{{$sk.StatusAsHTML}}{{end}}</td>
</tr>
{{end}}
</table>
`
)
// ResilientSrvTopoServer is an implementation of SrvTopoServer based
// on a topo.Server that uses a cache for two purposes:
// - limit the QPS to the underlying topo.Server
// - return the last known value of the data if there is an error
type ResilientSrvTopoServer struct {
topoServer topo.Server
cacheTTL time.Duration
counts *stats.Counters
// mutex protects the cache map itself, not the individual
// values in the cache.
mutex sync.RWMutex
srvKeyspaceNamesCache map[string]*srvKeyspaceNamesEntry
srvKeyspaceCache map[string]*srvKeyspaceEntry
}
type srvKeyspaceNamesEntry struct {
// unmutable values
cell string
// the mutex protects any access to this structure (read or write)
mutex sync.Mutex
insertionTime time.Time
value []string
lastError error
lastErrorCtx context.Context
}
type srvKeyspaceEntry struct {
// unmutable values
cell string
keyspace string
// the mutex protects any access to this structure (read or write)
mutex sync.RWMutex
// watchRunning describes if the watch go routine is running.
// It is easier to have an explicit field instead of guessing
// based on value and lastError.
//
// if watchrunning is not set, the next time we try to access the
// keyspace, we will start a watch.
// if watchrunning is set, we are guaranteed to have exactly one of
// value or lastError be nil, and the other non-nil.
watchRunning bool
value *topodatapb.SrvKeyspace
lastError error
// lastErrorCtx tries to remember the context of the query
// that failed to get the SrvKeyspace, so we can display it in
// the status UI. The background routine that refreshes the
// keyspace will not populate this field.
// The intent is to have the source of a query that for instance
// has a bad keyspace or cell name.
lastErrorCtx context.Context
}
// NewResilientSrvTopoServer creates a new ResilientSrvTopoServer
// based on the provided topo.Server.
func NewResilientSrvTopoServer(base topo.Server, counterPrefix string) *ResilientSrvTopoServer {
return &ResilientSrvTopoServer{
topoServer: base,
cacheTTL: *srvTopoCacheTTL,
counts: stats.NewCounters(counterPrefix + "Counts"),
srvKeyspaceNamesCache: make(map[string]*srvKeyspaceNamesEntry),
srvKeyspaceCache: make(map[string]*srvKeyspaceEntry),
}
}
// GetSrvKeyspaceNames returns all keyspace names for the given cell.
func (server *ResilientSrvTopoServer) GetSrvKeyspaceNames(ctx context.Context, cell string) ([]string, error) {
server.counts.Add(queryCategory, 1)
// find the entry in the cache, add it if not there
key := cell
server.mutex.Lock()
entry, ok := server.srvKeyspaceNamesCache[key]
if !ok {
entry = &srvKeyspaceNamesEntry{
cell: cell,
}
server.srvKeyspaceNamesCache[key] = entry
}
server.mutex.Unlock()
// Lock the entry, and do everything holding the lock. This
// means two concurrent requests will only issue one
// underlying query.
entry.mutex.Lock()
defer entry.mutex.Unlock()
// If the entry is fresh enough, return it
if time.Now().Sub(entry.insertionTime) < server.cacheTTL {
return entry.value, entry.lastError
}
// not in cache or too old, get the real value
newCtx, cancel := context.WithTimeout(context.Background(), *srvTopoTimeout)
defer cancel()
result, err := server.topoServer.GetSrvKeyspaceNames(newCtx, cell)
if err != nil {
if entry.insertionTime.IsZero() {
server.counts.Add(errorCategory, 1)
log.Errorf("GetSrvKeyspaceNames(%v, %v) failed: %v (no cached value, caching and returning error)", newCtx, cell, err)
} else {
server.counts.Add(cachedCategory, 1)
log.Warningf("GetSrvKeyspaceNames(%v, %v) failed: %v (returning cached value: %v %v)", newCtx, cell, err, entry.value, entry.lastError)
return entry.value, entry.lastError
}
}
// save the value we got and the current time in the cache
entry.insertionTime = time.Now()
entry.value = result
entry.lastError = err
entry.lastErrorCtx = newCtx
return result, err
}
// WatchSrvVSchema is part of the SrvTopoServer API
func (server *ResilientSrvTopoServer) WatchSrvVSchema(ctx context.Context, cell string) (*topo.WatchSrvVSchemaData, <-chan *topo.WatchSrvVSchemaData, topo.CancelFunc) {
return server.topoServer.WatchSrvVSchema(ctx, cell)
}
func (server *ResilientSrvTopoServer) getSrvKeyspaceEntry(cell, keyspace string) *srvKeyspaceEntry {
// find the entry in the cache, add it if not there
key := cell + "." + keyspace
server.mutex.RLock()
entry, ok := server.srvKeyspaceCache[key]
if ok {
server.mutex.RUnlock()
return entry
}
server.mutex.RUnlock()
server.mutex.Lock()
entry, ok = server.srvKeyspaceCache[key]
if !ok {
entry = &srvKeyspaceEntry{
cell: cell,
keyspace: keyspace,
}
server.srvKeyspaceCache[key] = entry
}
server.mutex.Unlock()
return entry
}
// GetSrvKeyspace returns SrvKeyspace object for the given cell and keyspace.
func (server *ResilientSrvTopoServer) GetSrvKeyspace(ctx context.Context, cell, keyspace string) (*topodatapb.SrvKeyspace, error) {
entry := server.getSrvKeyspaceEntry(cell, keyspace)
// If the watch is already running, return the value
entry.mutex.RLock()
if entry.watchRunning {
v, e := entry.value, entry.lastError
entry.mutex.RUnlock()
return v, e
}
entry.mutex.RUnlock()
// Lock the entry, and do everything holding the lock. This
// means two concurrent requests will only issue one
// underlying query.
entry.mutex.Lock()
defer entry.mutex.Unlock()
// If the watch is already running, return the value
if entry.watchRunning {
return entry.value, entry.lastError
}
// Watch is not running, let's try to start it.
// We use a background context, as starting the watch should keep going
// even if the current query context is short-lived.
newCtx := context.Background()
current, changes, _ := server.topoServer.WatchSrvKeyspace(newCtx, cell, keyspace)
if current.Err != nil {
// lastError and lastErrorCtx will be visible from the UI
// until the next try
entry.value = nil
entry.lastError = current.Err
entry.lastErrorCtx = ctx
log.Errorf("WatchSrvKeyspace failed for %v/%v: %v", cell, keyspace, current.Err)
return nil, current.Err
}
// we are now watching, cache the first notification
entry.watchRunning = true
entry.value = current.Value
entry.lastError = nil
entry.lastErrorCtx = nil
go func() {
for c := range changes {
if c.Err != nil {
// Watch errored out. We log it, clear
// our record, and return.
err := fmt.Errorf("watch for SrvKeyspace %v in cell %v failed: %v", keyspace, cell, c.Err)
log.Errorf("%v", err)
entry.mutex.Lock()
entry.watchRunning = false
entry.value = nil
entry.lastError = err
entry.lastErrorCtx = nil
entry.mutex.Unlock()
return
}
// We got a new value, save it.
entry.mutex.Lock()
entry.value = c.Value
entry.lastError = nil
entry.lastErrorCtx = nil
entry.mutex.Unlock()
}
}()
return entry.value, entry.lastError
}
// The next few structures and methods are used to get a displayable
// version of the cache in a status page.
// SrvKeyspaceNamesCacheStatus is the current value for SrvKeyspaceNames
type SrvKeyspaceNamesCacheStatus struct {
Cell string
Value []string
LastError error
LastErrorCtx context.Context
}
// SrvKeyspaceNamesCacheStatusList is used for sorting
type SrvKeyspaceNamesCacheStatusList []*SrvKeyspaceNamesCacheStatus
// Len is part of sort.Interface
func (skncsl SrvKeyspaceNamesCacheStatusList) Len() int {
return len(skncsl)
}
// Less is part of sort.Interface
func (skncsl SrvKeyspaceNamesCacheStatusList) Less(i, j int) bool {
return skncsl[i].Cell < skncsl[j].Cell
}
// Swap is part of sort.Interface
func (skncsl SrvKeyspaceNamesCacheStatusList) Swap(i, j int) {
skncsl[i], skncsl[j] = skncsl[j], skncsl[i]
}
// SrvKeyspaceCacheStatus is the current value for a SrvKeyspace object
type SrvKeyspaceCacheStatus struct {
Cell string
Keyspace string
Value *topodatapb.SrvKeyspace
LastError error
LastErrorCtx context.Context
}
// StatusAsHTML returns an HTML version of our status.
// It works best if there is data in the cache.
func (st *SrvKeyspaceCacheStatus) StatusAsHTML() template.HTML {
if st.Value == nil {
return template.HTML("No Data")
}
result := "<b>Partitions:</b><br>"
for _, keyspacePartition := range st.Value.Partitions {
result += " <b>" + keyspacePartition.ServedType.String() + ":</b>"
for _, shard := range keyspacePartition.ShardReferences {
result += " " + shard.Name
}
result += "<br>"
}
if st.Value.ShardingColumnName != "" {
result += "<b>ShardingColumnName:</b> " + st.Value.ShardingColumnName + "<br>"
result += "<b>ShardingColumnType:</b> " + st.Value.ShardingColumnType.String() + "<br>"
}
if len(st.Value.ServedFrom) > 0 {
result += "<b>ServedFrom:</b><br>"
for _, sf := range st.Value.ServedFrom {
result += " <b>" + sf.TabletType.String() + ":</b> " + sf.Keyspace + "<br>"
}
}
return template.HTML(result)
}
// SrvKeyspaceCacheStatusList is used for sorting
type SrvKeyspaceCacheStatusList []*SrvKeyspaceCacheStatus
// Len is part of sort.Interface
func (skcsl SrvKeyspaceCacheStatusList) Len() int {
return len(skcsl)
}
// Less is part of sort.Interface
func (skcsl SrvKeyspaceCacheStatusList) Less(i, j int) bool {
return skcsl[i].Cell+"."+skcsl[i].Keyspace <
skcsl[j].Cell+"."+skcsl[j].Keyspace
}
// Swap is part of sort.Interface
func (skcsl SrvKeyspaceCacheStatusList) Swap(i, j int) {
skcsl[i], skcsl[j] = skcsl[j], skcsl[i]
}
// ResilientSrvTopoServerCacheStatus has the full status of the cache
type ResilientSrvTopoServerCacheStatus struct {
SrvKeyspaceNames SrvKeyspaceNamesCacheStatusList
SrvKeyspaces SrvKeyspaceCacheStatusList
}
// CacheStatus returns a displayable version of the cache
func (server *ResilientSrvTopoServer) CacheStatus() *ResilientSrvTopoServerCacheStatus {
result := &ResilientSrvTopoServerCacheStatus{}
server.mutex.Lock()
for _, entry := range server.srvKeyspaceNamesCache {
entry.mutex.Lock()
result.SrvKeyspaceNames = append(result.SrvKeyspaceNames, &SrvKeyspaceNamesCacheStatus{
Cell: entry.cell,
Value: entry.value,
LastError: entry.lastError,
LastErrorCtx: entry.lastErrorCtx,
})
entry.mutex.Unlock()
}
for _, entry := range server.srvKeyspaceCache {
entry.mutex.RLock()
result.SrvKeyspaces = append(result.SrvKeyspaces, &SrvKeyspaceCacheStatus{
Cell: entry.cell,
Keyspace: entry.keyspace,
Value: entry.value,
LastError: entry.lastError,
LastErrorCtx: entry.lastErrorCtx,
})
entry.mutex.RUnlock()
}
server.mutex.Unlock()
// do the sorting without the mutex
sort.Sort(result.SrvKeyspaceNames)
sort.Sort(result.SrvKeyspaces)
return result
}