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lists.go
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lists.go
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/*
* Copyright (C) 2017 Dgraph Labs, Inc. and Contributors
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package posting
import (
"crypto/md5"
"fmt"
"io/ioutil"
"math"
"os"
"os/exec"
"runtime"
"strconv"
"strings"
"sync"
"time"
"golang.org/x/net/trace"
"github.com/dgraph-io/badger"
"gopkg.in/adibiarsotp/dgraph.v83/protos"
"gopkg.in/adibiarsotp/dgraph.v83/x"
)
var (
dummyPostingList []byte // Used for indexing.
elog trace.EventLog
)
const (
MB = 1 << 20
)
// syncMarks stores the watermark for synced RAFT proposals. Each RAFT proposal consists
// of many individual mutations, which could be applied to many different posting lists.
// Thus, each PL when being mutated would send an undone Mark, and each list would
// accumulate all such pending marks. When the PL is synced to RocksDB, it would
// mark all the pending ones as done.
// This ideally belongs to RAFT node struct (where committed watermark is being tracked),
// but because the logic of mutations is
// present here and to avoid a circular dependency, we've placed it here.
// Note that there's one watermark for each RAFT node/group.
// This watermark would be used for taking snapshots, to ensure that all the data and
// index mutations have been syned to RocksDB, before a snapshot is taken, and previous
// RAFT entries discarded.
func init() {
x.AddInit(func() {
h := md5.New()
pl := protos.PostingList{
Checksum: h.Sum(nil),
}
var err error
dummyPostingList, err = pl.Marshal()
x.Check(err)
})
elog = trace.NewEventLog("Memory", "")
}
func gentleCommit(dirtyMap map[string]time.Time, pending chan struct{},
commitFraction float64) {
select {
case pending <- struct{}{}:
default:
elog.Printf("Skipping gentleCommit")
return
}
// NOTE: No need to acquire read lock for stopTheWorld. This portion is being run
// serially alongside aggressive commit.
n := int(float64(len(dirtyMap)) * commitFraction)
if n < 1000 {
// Have a min value of n, so we can merge small number of dirty PLs fast.
n = 1000
}
keysBuffer := make([]string, 0, n)
// Convert map to list.
var loops int
for key, ts := range dirtyMap {
loops++
if loops > 3*n {
break
}
if time.Since(ts) < 5*time.Second {
continue
}
delete(dirtyMap, key)
keysBuffer = append(keysBuffer, key)
if len(keysBuffer) >= n {
// We don't want to process the entire dirtyMap in one go.
break
}
}
go func(keys []string) {
defer func() { <-pending }()
if len(keys) == 0 {
return
}
for _, key := range keys {
l := lcache.Get(key)
if l == nil {
continue
}
// Not removing the postings list from the map, to avoid a race condition,
// where another caller re-creates the posting list before a commit happens.
commitOne(l)
}
}(keysBuffer)
}
func getMemUsage() int {
if runtime.GOOS != "linux" {
pid := os.Getpid()
cmd := fmt.Sprintf("ps -ao rss,pid | grep %v", pid)
c1, err := exec.Command("bash", "-c", cmd).Output()
if err != nil {
// In case of error running the command, resort to go way
var ms runtime.MemStats
runtime.ReadMemStats(&ms)
megs := ms.Alloc
return int(megs)
}
rss := strings.Split(string(c1), " ")[0]
kbs, err := strconv.Atoi(rss)
if err != nil {
return 0
}
megs := kbs << 10
return megs
}
contents, err := ioutil.ReadFile("/proc/self/stat")
if err != nil {
x.Println("Can't read the proc file", err)
return 0
}
cont := strings.Split(string(contents), " ")
// 24th entry of the file is the RSS which denotes the number of pages
// used by the process.
if len(cont) < 24 {
x.Println("Error in RSS from stat")
return 0
}
rss, err := strconv.Atoi(cont[23])
if err != nil {
x.Println(err)
return 0
}
return rss * os.Getpagesize()
}
// periodicMerging periodically merges the dirty posting lists. It also checks our memory
// usage. If it exceeds a certain threshold, it would stop the world, and aggressively
// merge and evict all posting lists from memory.
func periodicCommit() {
ticker := time.NewTicker(time.Second)
dirtyMap := make(map[string]time.Time, 1000)
// pending is used to ensure that we only have up to 15 goroutines doing gentle commits.
pending := make(chan struct{}, 15)
dsize := 0 // needed for better reporting.
setLruMemory := true
for {
select {
case key := <-dirtyChan:
dirtyMap[string(key)] = time.Now()
case <-ticker.C:
if len(dirtyMap) != dsize {
dsize = len(dirtyMap)
x.DirtyMapSize.Set(int64(dsize))
}
var ms runtime.MemStats
runtime.ReadMemStats(&ms)
megs := (ms.HeapInuse + ms.StackInuse) / (1 << 20)
inUse := float64(megs)
fraction := math.Min(1.0, Config.CommitFraction*math.Exp(float64(dsize)/1000000.0))
gentleCommit(dirtyMap, pending, fraction)
stats := lcache.Stats()
x.EvictedPls.Set(int64(stats.NumEvicts))
x.LcacheSize.Set(int64(stats.Size))
x.LcacheLen.Set(int64(stats.Length))
// Flush out the dirtyChan after acquiring lock. This allow posting lists which
// are currently being processed to not get stuck on dirtyChan, which won't be
// processed until aggressive evict finishes.
// Okay, we exceed the max memory threshold.
// Stop the world, and deal with this first.
x.NumGoRoutines.Set(int64(runtime.NumGoroutine()))
Config.Mu.Lock()
mem := Config.AllottedMemory
Config.Mu.Unlock()
if setLruMemory && inUse > 0.75*mem {
lcache.UpdateMaxSize()
setLruMemory = false
}
}
}
}
func updateMemoryMetrics() {
ticker := time.NewTicker(time.Minute)
for range ticker.C {
var ms runtime.MemStats
runtime.ReadMemStats(&ms)
megs := (ms.HeapInuse + ms.StackInuse)
inUse := float64(megs)
idle := float64(ms.HeapIdle - ms.HeapReleased)
x.MemoryInUse.Set(int64(inUse))
x.HeapIdle.Set(int64(idle))
x.TotalOSMemory.Set(int64(getMemUsage()))
}
}
var (
pstore *badger.KV
dirtyChan chan []byte // All dirty posting list keys are pushed here.
marks *x.WaterMark
lcache *listCache
)
func SyncMarks() *x.WaterMark {
return marks
}
// Init initializes the posting lists package, the in memory and dirty list hash.
func Init(ps *badger.KV) {
marks = &x.WaterMark{Name: "Synced watermark"}
marks.Init()
pstore = ps
lcache = newListCache(math.MaxUint64)
x.LcacheCapacity.Set(math.MaxInt64)
dirtyChan = make(chan []byte, 10000)
go periodicCommit()
go updateMemoryMetrics()
}
// Get stores the List corresponding to key, if it's not there already.
// to lru cache and returns it.
//
// plist := Get(key, group)
// ... // Use plist
// TODO: This should take a node id and index. And just append all indices to a list.
// When doing a commit, it should update all the sync index watermarks.
// worker pkg would push the indices to the watermarks held by lists.
// And watermark stuff would have to be located outside worker pkg, maybe in x.
// That way, we don't have a dependency conflict.
func Get(key []byte) (rlist *List) {
lp := lcache.Get(string(key))
if lp != nil {
x.CacheHit.Add(1)
return lp
}
x.CacheMiss.Add(1)
// Any initialization for l must be done before PutIfMissing. Once it's added
// to the map, any other goroutine can retrieve it.
l := getNew(key, pstore)
l.water = marks
// We are always going to return lp to caller, whether it is l or not
lp = lcache.PutIfMissing(string(key), l)
if lp != l {
x.CacheRace.Add(1)
}
return lp
}
// getOrMutate is similar to GetLru the only difference being that for index and count keys it also
// does a SetIfAbsentAsync. This function should be called by functions in the mutation path only.
func getOrMutate(key []byte) (rlist *List) {
lp := lcache.Get(string(key))
if lp != nil {
x.CacheHit.Add(1)
return lp
}
x.CacheMiss.Add(1)
// Any initialization for l must be done before PutIfMissing. Once it's added
// to the map, any other goroutine can retrieve it.
l := getNew(key, pstore)
l.water = marks
// We are always going to return lp to caller, whether it is l or not
lp = lcache.PutIfMissing(string(key), l)
if lp != l {
x.CacheRace.Add(1)
} else {
pk := x.Parse(key)
x.AssertTrue(pk.IsIndex() || pk.IsCount())
// This is a best effort set, hence we don't check error from callback.
if err := pstore.SetIfAbsentAsync(key, nil, 0x00, func(err error) {}); err != nil &&
err != badger.ErrKeyExists {
x.Fatalf("Got error while doing SetIfAbsent: %+v\n", err)
}
}
return lp
}
// GetNoStore takes a key. It checks if the in-memory map has an updated value and returns it if it exists
// or it gets from the store and DOES NOT ADD to lru cache.
func GetNoStore(key []byte) (rlist *List) {
lp := lcache.Get(string(key))
if lp != nil {
return lp
}
lp = getNew(key, pstore) // This retrieves a new *List and sets refcount to 1.
return lp
}
func commitOne(l *List) {
if l == nil {
return
}
if _, err := l.SyncIfDirty(false); err != nil {
x.Printf("Error while committing dirty list: %v\n", err)
}
}
func CommitLists(numRoutines int, gid uint32) {
if gid == 0 {
return
}
// We iterate over lhmap, deleting keys and pushing values (List) into this
// channel. Then goroutines right below will commit these lists to data store.
workChan := make(chan *List, 10000)
var wg sync.WaitGroup
for i := 0; i < numRoutines; i++ {
wg.Add(1)
go func() {
defer wg.Done()
for l := range workChan {
commitOne(l)
}
}()
}
lcache.Each(func(k []byte, l *List) {
if l == nil { // To be safe. Check might be unnecessary.
return
}
workChan <- l
})
close(workChan)
wg.Wait()
}
// This doesn't sync, so call this only when you don't care about dirty posting lists in
// memory(for example before populating snapshot) or after calling syncAllMarks
func EvictLRU() {
lcache.Reset()
}