forked from dgraph-io/dgraph
/
lists.go
498 lines (438 loc) · 12.6 KB
/
lists.go
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/*
* Copyright 2015 DGraph Labs, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package posting
import (
"context"
"crypto/md5"
"flag"
"fmt"
"io/ioutil"
"log"
"os"
"os/exec"
"runtime"
"runtime/debug"
"strconv"
"strings"
"sync"
"sync/atomic"
"time"
"github.com/dgryski/go-farm"
"github.com/dgraph-io/dgraph/store"
"github.com/dgraph-io/dgraph/types"
"github.com/dgraph-io/dgraph/x"
)
var (
maxmemory = flag.Int("stw_ram_mb", 4096,
"If RAM usage exceeds this, we stop the world, and flush our buffers.")
commitFraction = flag.Float64("gentlecommit", 0.10, "Fraction of dirty posting lists to commit every few seconds.")
lhmapNumShards = flag.Int("lhmap", 32, "Number of shards for lhmap.")
dummyPostingList []byte // Used for indexing.
)
// 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.
type syncMarks struct {
sync.RWMutex
m map[uint32]*x.WaterMark
}
func init() {
x.AddInit(func() {
h := md5.New()
pl := types.PostingList{
Checksum: h.Sum(nil),
}
var err error
dummyPostingList, err = pl.Marshal()
x.Check(err)
})
}
func (g *syncMarks) create(group uint32) *x.WaterMark {
g.Lock()
defer g.Unlock()
if g.m == nil {
g.m = make(map[uint32]*x.WaterMark)
}
if prev, present := g.m[group]; present {
return prev
}
w := &x.WaterMark{Name: fmt.Sprintf("Synced: Group %d", group)}
w.Init()
g.m[group] = w
return w
}
func (g *syncMarks) Get(group uint32) *x.WaterMark {
g.RLock()
if w, present := g.m[group]; present {
g.RUnlock()
return w
}
g.RUnlock()
return g.create(group)
}
// SyncMarkFor returns the synced watermark for the given RAFT group.
// We use this to determine the index to use when creating a new snapshot.
func SyncMarkFor(group uint32) *x.WaterMark {
return marks.Get(group)
}
type counters struct {
ticker *time.Ticker
done uint64
noop uint64
lastVal uint64
}
func (c *counters) periodicLog() {
for _ = range c.ticker.C {
c.log()
}
}
func (c *counters) log() {
done := atomic.LoadUint64(&c.done)
noop := atomic.LoadUint64(&c.noop)
lastVal := atomic.LoadUint64(&c.lastVal)
if done == lastVal {
// Ignore.
return
}
atomic.StoreUint64(&c.lastVal, done)
log.Printf("Commit counters. done: %5d noop: %5d\n", done, noop)
}
func newCounters() *counters {
c := new(counters)
c.ticker = time.NewTicker(time.Second)
go c.periodicLog()
return c
}
func aggressivelyEvict() {
// Okay, we exceed the max memory threshold.
// Stop the world, and deal with this first.
megs := getMemUsage()
log.Printf("Memory usage over threshold. STW. Allocated MB: %v\n", megs)
log.Println("Aggressive evict, committing to RocksDB")
CommitLists(1)
log.Println("Trying to free OS memory")
// Forces garbage collection followed by returning as much memory to the OS
// as possible.
debug.FreeOSMemory()
megs = getMemUsage()
log.Printf("EVICT DONE! Memory usage after calling GC. Allocated MB: %v", megs)
}
func gentleCommit(dirtyMap map[uint64]struct{}, pending chan struct{}) {
select {
case pending <- struct{}{}:
default:
fmt.Println("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([]uint64, 0, n)
for key := range dirtyMap {
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 []uint64) {
defer func() { <-pending }()
if len(keys) == 0 {
return
}
ctr := newCounters()
defer ctr.ticker.Stop()
for _, key := range keys {
l, ok := lhmap.Get(key)
if !ok || 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, ctr)
}
ctr.log()
}(keysBuffer)
}
// 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(5 * time.Second)
dirtyMap := make(map[uint64]struct{}, 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.
for {
select {
case key := <-dirtyChan:
dirtyMap[key] = struct{}{}
case <-ticker.C:
if len(dirtyMap) != dsize {
dsize = len(dirtyMap)
log.Printf("Dirty map size: %d\n", dsize)
}
totMemory := getMemUsage()
if totMemory <= *maxmemory {
gentleCommit(dirtyMap, pending)
break
}
// Do aggressive commit, which would delete all the PLs from memory.
// Acquire lock, so no new posting lists are given out.
stopTheWorld.Lock()
DIRTYLOOP:
// 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.
for {
select {
case <-dirtyChan:
// pass
default:
break DIRTYLOOP
}
}
aggressivelyEvict()
for k := range dirtyMap {
delete(dirtyMap, k)
}
stopTheWorld.Unlock()
}
}
}
// getMemUsage returns the amount of memory used by the process in MB
func getMemUsage() int {
var ms runtime.MemStats
runtime.ReadMemStats(&ms)
megs := ms.Alloc / (1 << 20)
return int(megs)
// Sticking to ms.Alloc temoprarily.
// TODO(Ashwin): Switch to total Memory(RSS) once we figure out
// how to release memory to OS (Currently only a small chunk
// is returned)
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 / (1 << 20)
return int(megs)
}
rss := strings.Split(string(c1), " ")[0]
kbs, err := strconv.Atoi(rss)
if err != nil {
return 0
}
megs := kbs / (1 << 10)
return megs
}
contents, err := ioutil.ReadFile("/proc/self/stat")
if err != nil {
log.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 {
log.Println("Error in RSS from stat")
return 0
}
rss, err := strconv.Atoi(cont[23])
if err != nil {
log.Println(err)
return 0
}
return rss * os.Getpagesize() / (1 << 20)
}
var (
stopTheWorld sync.RWMutex
lhmap *listMap
pstore *store.Store
syncCh chan syncEntry
dirtyChan chan uint64 // All dirty posting list keys are pushed here.
marks *syncMarks
)
// Init initializes the posting lists package, the in memory and dirty list hash.
func Init(ps *store.Store) {
marks = new(syncMarks)
pstore = ps
lhmap = newShardedListMap(*lhmapNumShards)
dirtyChan = make(chan uint64, 10000)
fmt.Println("Starting commit routine.")
syncCh = make(chan syncEntry, 10000)
go periodicCommit()
go batchSync()
}
func getFromMap(key uint64) *List {
lp, _ := lhmap.Get(key)
if lp == nil {
return nil
}
lp.incr()
return lp
}
// GetOrCreate stores the List corresponding to key, if it's not there already.
// to lhmap and returns it. It also returns a reference decrement function to be called by caller.
//
// plist, decr := GetOrCreate(key, store)
// defer decr()
// ... // 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 GetOrCreate(key []byte, group uint32) (rlist *List, decr func()) {
fp := farm.Fingerprint64(key)
stopTheWorld.RLock()
defer stopTheWorld.RUnlock()
lp, _ := lhmap.Get(fp)
if lp != nil {
lp.incr()
return lp, lp.decr
}
// 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) // This retrieves a new *List and sets refcount to 1.
l.water = marks.Get(group)
lp = lhmap.PutIfMissing(fp, l)
// We are always going to return lp to caller, whether it is l or not. So, let's
// increment its reference counter.
lp.incr()
if lp != l {
// Undo the increment in getNew() call above.
l.decr()
}
pk := x.Parse(key)
// This replaces "TokensTable". The idea is that we want to quickly add the
// index key to the data store, with essentially an empty value. We just need
// the keys for filtering / sorting.
if l == lp && pk.IsIndex() {
// Lock before entering goroutine. Otherwise, some tests in query will fail.
l.Lock()
go func(key []byte) {
defer l.Unlock()
slice, err := pstore.Get(key)
x.Check(err)
if slice.Size() == 0 {
x.Check(pstore.SetOne(key, dummyPostingList))
}
}(key)
}
return lp, lp.decr
}
func commitOne(l *List, c *counters) {
if l == nil {
return
}
if merged, err := l.SyncIfDirty(context.Background()); err != nil {
log.Printf("Error while commiting dirty list: %v\n", err)
} else if merged {
atomic.AddUint64(&c.done, 1)
} else {
atomic.AddUint64(&c.noop, 1)
}
}
func CommitLists(numRoutines int) {
c := newCounters()
defer c.ticker.Stop()
// 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 {
l.SetForDeletion() // No more AddMutation.
commitOne(l, c)
l.decr()
}
}()
}
lhmap.EachWithDelete(func(k uint64, l *List) {
if l == nil { // To be safe. Check might be unnecessary.
return
}
// We lose one reference for deletion from lhmap. But we gain one reference
// for pushing into workChan. So no decr or incr here.
workChan <- l
})
close(workChan)
wg.Wait()
}
// The following logic is used to batch up all the writes to RocksDB.
type syncEntry struct {
key []byte
val []byte
water *x.WaterMark
pending []uint64
sw *x.SafeWait
}
func batchSync() {
var entries []syncEntry
var loop uint64
b := pstore.NewWriteBatch()
defer b.Destroy()
for {
select {
case e := <-syncCh:
entries = append(entries, e)
default:
// default is executed if no other case is ready.
start := time.Now()
if len(entries) > 0 {
x.AssertTrue(b != nil)
loop++
fmt.Printf("[%4d] Writing batch of size: %v\n", loop, len(entries))
for _, e := range entries {
b.Put(e.key, e.val)
}
x.Checkf(pstore.WriteBatch(b), "Error while writing to RocksDB.")
b.Clear()
for _, e := range entries {
e.sw.Done()
if e.water != nil {
e.water.Ch <- x.Mark{Indices: e.pending, Done: true}
}
}
entries = entries[:0]
}
// Add a sleep clause to avoid a busy wait loop if there's no input to commitCh.
sleepFor := 10*time.Millisecond - time.Since(start)
time.Sleep(sleepFor)
}
}
}