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distribute: Make server work with multiple remote disks

Browse Source 
This change initializes rpc servers associated with disks that are
local. It makes object layer initialization on demand, namely on the
first request to the object layer.

Also adds lock RPC service vendorized minio/dsync
This commit is contained in:
Krishnan Parthasarathi
2016-07-31 14:11:14 -07:00
committed by Harshavardhana
parent f82f535509
commit e55926e8cf
24 changed files with 1312 additions and 115 deletions
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vendor/github.com/minio/dsync/LICENSE generated vendored Normal file
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81
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dsync
=====
A distributed sync package.
Introduction
------------
`dsync` is a package for doing distributed locks over a network of `n` nodes. It is designed with simplicity in mind and hence offers limited scalability (`n <= 16`). Each node will be connected to all other nodes and lock requests from any node will be broadcast to all connected nodes. A node will succeed in getting the lock if `n/2 + 1` nodes (including itself) respond positively. If the lock is acquired it can be held for some time and needs to be released afterwards. This will cause the release to be broadcast to all nodes after which the lock becomes available again.
Design goals
------------
* Simple design: by keeping the design simple, many tricky edge cases can be avoided.
* No master node: there is no concept of a master node which, if this would be used and the master would be down, causes locking to come to a complete stop. (Unless you have a design with a slave node but this adds yet more complexity.)
* Resilient: if one or more nodes go down, the other nodes should not be affected and can continue to acquire locks (provided not more than `n/2 - 1` nodes are down).
* Automatically reconnect to (restarted) nodes.
* Compatible with `sync/mutex` API.
Restrictions
------------
* Limited scalability: up to 16 nodes.
* Fixed configuration: changes in the number and/or network names/IP addresses need a restart of all nodes in order to take effect.
* If a down node comes up, it will not in any way (re)acquire any locks that it may have held.
* Not designed for high performance applications such as key/value stores
Performance
-----------
* Lock requests (successful) should not take longer than 1ms (provided decent network connection of 1 Gbit or more between the nodes)
* Support up to 4000 locks per node per second.
* Scale linearly with the number of locks. For the maximum size case of 16 nodes this means a maximum of 64K locks/sec (and 2048K lock request & release messages/sec)
* Do not take more than (overall) 10% CPU usage
Issues
------
* In case the node that has the lock goes down, the lock release will not be broadcast: what do we do? (periodically ping 'back' to requesting node from all nodes that have the lock?) Or detect that the network connection has gone down.
* If one of the nodes that participated in the lock goes down, this is not a problem since (when it comes back online) the node that originally acquired the lock will still have it, and a request for a new lock will fail due to only `n/2` being available.
* If two nodes go down and both participated in the lock then there is a chance that a new lock will acquire locks from `n/2 + 1` nodes and will success, so we would have two concurrent locks. One way to counter this would be to monitor the network connections from the nodes that originated the lock, and, upon losing a connection to a node that granted a lock, get a new lock from a free node.
* When two nodes want to acquire the same lock, it is possible for both to just acquire `n` locks and there is no majority winner so both would fail (and presumably fail back to their clients?). This then requires a retry in order to acquire the lock at a later time.
* What if late acquire response still comes in after lock has been obtained (quorum is in) and has already been released again.
Comparison to other techniques
------------------------------
We are well aware that there are more sophisticated systems such as zookeeper, raft, etc but we found that for our limited use case this was adding too much complexity. So if `dsync` does not meet your requirements than you are probably better off using one of those systems.
Performance
-----------
```
benchmark old ns/op new ns/op delta
BenchmarkMutexUncontended-8 4.22 1164018 +27583264.93%
BenchmarkMutex-8 96.5 1223266 +1267533.16%
BenchmarkMutexSlack-8 120 1192900 +993983.33%
BenchmarkMutexWork-8 108 1239893 +1147949.07%
BenchmarkMutexWorkSlack-8 142 1210129 +852103.52%
BenchmarkMutexNoSpin-8 292 319479 +109310.62%
BenchmarkMutexSpin-8 1163 1270066 +109106.02%
```
Usage
-----
Explain usage
```
```
License
-------
Released under the Apache License v2.0. You can find the complete text in the file LICENSE.
Contributing
------------
Contributions are welcome, please send PRs for any enhancements.

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vendor/github.com/minio/dsync/dmutex.go generated vendored Normal file
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/*
* Minio Cloud Storage, (C) 2016 Minio, 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 dsync
import (
"log"
"math"
"math/rand"
"net/rpc"
"strings"
"sync"
"time"
)
const DMutexAcquireTimeout = 25 * time.Millisecond
// A DMutex is a distributed mutual exclusion lock.
type DMutex struct {
Name string
locks []bool // Array of nodes that granted a lock
uids []string // Array of uids for verification of sending correct release messages
m sync.Mutex // Mutex to prevent multiple simultaneous locks from this node
// TODO: Decide: create per object or create once for whole class
clnts []*rpc.Client
}
type Granted struct {
index int
locked bool
uid string
}
func connectLazy(dm *DMutex) {
if dm.clnts == nil {
dm.clnts = make([]*rpc.Client, n)
}
for i := range dm.clnts {
if dm.clnts[i] == nil {
// pass in unique path (as required by server.HandleHTTP()
dm.clnts[i], _ = rpc.DialHTTPPath("tcp", nodes[i], rpcPath+"-"+strings.Split(nodes[i], ":")[1])
}
}
}
// Lock locks dm.
//
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (dm *DMutex) Lock() {
// Shield Lock() with local mutex in order to prevent more than
// one broadcast going out at the same time from this node
dm.m.Lock()
defer dm.m.Unlock()
runs, backOff := 1, 1
for {
// TODO: Implement reconnect
connectLazy(dm)
// create temp arrays on stack
locks := make([]bool, n)
ids := make([]string, n)
// try to acquire the lock
success := lock(dm.clnts, &locks, &ids, dm.Name)
if success {
// if success, copy array to object
dm.locks = make([]bool, n)
copy(dm.locks, locks[:])
dm.uids = make([]string, n)
copy(dm.uids, ids[:])
return
}
// We timed out on the previous lock, incrementally wait for a longer back-off time,
// and try again afterwards
time.Sleep(time.Duration(backOff) * time.Millisecond)
backOff += int(rand.Float64() * math.Pow(2, float64(runs)))
if backOff > 1024 {
backOff = backOff % 64
runs = 1 // reset runs
} else if runs < 10 {
runs++
}
}
}
func (dm *DMutex) tryLockTimeout() bool {
// Shield Lock() with local mutex in order to prevent more than
// one broadcast going out at the same time from this node
dm.m.Lock()
defer dm.m.Unlock()
// TODO: Implement reconnect
connectLazy(dm)
// create temp arrays on stack
locks := make([]bool, n)
ids := make([]string, n)
// try to acquire the lock
success := lock(dm.clnts, &locks, &ids, dm.Name)
if success {
// if success, copy array to object
dm.locks = make([]bool, n)
copy(dm.locks, locks[:])
dm.uids = make([]string, n)
copy(dm.uids, ids[:])
}
return success
}
// lock tries to acquire the distributed lock, returning true or false
//
func lock(clnts []*rpc.Client, locks *[]bool, uids *[]string, lockName string) bool {
// Create buffered channel of quorum size
ch := make(chan Granted, n/2+1)
for index, c := range clnts {
if c == nil {
continue
}
// broadcast lock request to all nodes
go func(index int, c *rpc.Client) {
// All client methods issuing RPCs are thread-safe and goroutine-safe,
// i.e. it is safe to call them from multiple concurrently running go routines.
var status bool
err := c.Call("Dsync.Lock", lockName, &status)
locked, uid := false, ""
if err == nil {
locked = status
// TODO: Get UIOD again
uid = ""
} else {
// silently ignore error, retry later
}
ch <- Granted{index: index, locked: locked, uid: uid}
}(index, c)
}
var wg sync.WaitGroup
wg.Add(1)
quorum := false
go func() {
// Wait until we have received (minimally) quorum number of responses or timeout
i := 0
done := false
timeout := time.After(DMutexAcquireTimeout)
for ; i < n; i++ {
select {
case grant := <-ch:
if grant.locked {
// Mark that this node has acquired the lock
(*locks)[grant.index] = true
(*uids)[grant.index] = grant.uid
} else {
done = true
//fmt.Println("one lock failed before quorum -- release locks acquired")
releaseAll(clnts, locks, uids, lockName)
}
case <-timeout:
done = true
// timeout happened, maybe one of the nodes is slow, count
// number of locks to check whether we have quorum or not
if !quorumMet(locks) {
//fmt.Println("timed out -- release locks acquired")
releaseAll(clnts, locks, uids, lockName)
}
}
if done {
break
}
}
// Count locks in order to determine whterh we have quorum or not
quorum = quorumMet(locks)
// Signal that we have the quorum
wg.Done()
// Wait for the other responses and immediately release the locks
// (do not add them to the locks array because the DMutex could
// already has been unlocked again by the original calling thread)
for ; i < n; i++ {
grantToBeReleased := <-ch
if grantToBeReleased.locked {
// release lock
go sendRelease(clnts[grantToBeReleased.index], lockName, grantToBeReleased.uid)
}
}
}()
wg.Wait()
return quorum
}
// quorumMet determines whether we have acquired n/2+1 underlying locks or not
func quorumMet(locks *[]bool) bool {
count := 0
for _, locked := range *locks {
if locked {
count++
}
}
return count >= n/2+1
}
// releaseAll releases all locks that are marked as locked
func releaseAll(clnts []*rpc.Client, locks *[]bool, ids *[]string, lockName string) {
for lock := 0; lock < n; lock++ {
if (*locks)[lock] {
go sendRelease(clnts[lock], lockName, (*ids)[lock])
(*locks)[lock] = false
(*ids)[lock] = ""
}
}
}
// hasLock returns whether or not a node participated in granting the lock
func (dm *DMutex) hasLock(node string) bool {
for index, n := range nodes {
if n == node {
return dm.locks[index]
}
}
return false
}
// locked returns whether or not we have met the quorum
func (dm *DMutex) locked() bool {
locks := make([]bool, n)
copy(locks[:], dm.locks[:])
return quorumMet(&locks)
}
// Unlock unlocks dm.
//
// It is a run-time error if dm is not locked on entry to Unlock.
func (dm *DMutex) Unlock() {
// Verify that we have the lock or panic otherwise (similar to sync.mutex)
if !dm.locked() {
panic("dsync: unlock of unlocked distributed mutex")
}
// We don't need to wait until we have released all the locks (or the quorum)
// (a subsequent lock will retry automatically in case it would fail to get
// quorum)
for index, c := range dm.clnts {
if dm.locks[index] {
// broadcast lock release to all nodes the granted the lock
go sendRelease(c, dm.Name, dm.uids[index])
dm.locks[index] = false
}
}
}
// sendRelease sends a release message to a node that previously granted a lock
func sendRelease(c *rpc.Client, name, uid string) {
// All client methods issuing RPCs are thread-safe and goroutine-safe,
// i.e. it is safe to call them from multiple concurrently running goroutines.
var status bool
// TODO: Send UID to server
if err := c.Call("Dsync.Unlock", name, &status); err != nil {
log.Fatal("Unlock on %s failed on client %v", name, c)
}
}

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vendor/github.com/minio/dsync/drwmutex.go generated vendored Normal file
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/*
* Minio Cloud Storage, (C) 2016 Minio, 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 dsync
import (
"fmt"
"sync"
)
const maxReaders = 8
type DRWMutex struct {
rArray []*DMutex
rLockedArray []bool
w DMutex // held if there are pending writers
m sync.Mutex // Mutex to prevent multiple simultaneous locks from this node
m2 sync.Mutex // Mutex to prevent multiple simultaneous locks from this node
}
func NewDRWMutex(name string) (drw *DRWMutex) {
rArray := make([]*DMutex, maxReaders)
rLockedArray := make([]bool, maxReaders)
for r := 0; r < maxReaders; r++ {
rArray[r] = &DMutex{Name: fmt.Sprintf("%s-r%d", name, r)}
}
return &DRWMutex{
rArray: rArray,
rLockedArray: rLockedArray,
w: DMutex{Name: name + "-w"}}
}
// RLock locks drw for reading.
func (drw *DRWMutex) RLock() {
drw.m.Lock()
defer drw.m.Unlock()
// Check if no write is active, block otherwise
// Can skip this?
drw.w.Lock()
drw.w.Unlock()
// Lock either one of the reader locks
for i := 0; ; i++ {
drw.rLockedArray[i%maxReaders] = drw.rArray[i%maxReaders].tryLockTimeout()
if drw.rLockedArray[i%maxReaders] {
return
}
}
}
// RUnlock undoes a single RLock call;
// it does not affect other simultaneous readers.
// It is a run-time error if rw is not locked for reading
// on entry to RUnlock.
func (drw *DRWMutex) RUnlock() {
drw.m.Lock()
defer drw.m.Unlock()
// Unlock whichever readlock that was acquired)
for r := 0; r < maxReaders; r++ {
if drw.rLockedArray[r] {
drw.rArray[r].Unlock()
drw.rLockedArray[r] = false
// we only want to release a single read lock at a time
break
}
}
}
// Lock locks rw for writing.
// If the lock is already locked for reading or writing,
// Lock blocks until the lock is available.
// To ensure that the lock eventually becomes available,
// a blocked Lock call excludes new readers from acquiring
// the lock.
func (drw *DRWMutex) Lock() {
drw.m.Lock()
defer drw.m.Unlock()
// First, resolve competition with other writers.
drw.w.Lock()
// Acquire all read locks.
var wg sync.WaitGroup
wg.Add(maxReaders)
for r := 0; r < maxReaders; r++ {
go func(r int) {
defer wg.Done()
drw.rArray[r].Lock()
drw.rLockedArray[r] = true
}(r)
}
wg.Wait()
}
// Unlock unlocks rw for writing. It is a run-time error if rw is
// not locked for writing on entry to Unlock.
//
// As with Mutexes, a locked RWMutex is not associated with a particular
// goroutine. One goroutine may RLock (Lock) an RWMutex and then
// arrange for another goroutine to RUnlock (Unlock) it.
func (drw *DRWMutex) Unlock() {
drw.m.Lock()
defer drw.m.Unlock()
for r := 0; r < maxReaders; r++ {
if !drw.rLockedArray[r] {
panic("dsync: unlock of unlocked distributed rwmutex")
}
}
// Unlock all read locks
for r := 0; r < maxReaders; r++ {
drw.rArray[r].Unlock()
drw.rLockedArray[r] = false
}
// Allow other writers to proceed.
drw.w.Unlock()
}

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vendor/github.com/minio/dsync/dsync.go generated vendored Normal file
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/*
* Minio Cloud Storage, (C) 2016 Minio, 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 dsync
import (
"errors"
"net/rpc"
)
const RpcPath = "/dsync"
const DebugPath = "/debug"
const DefaultPath = "/rpc/dsync"
var n int
var nodes []string
var rpcPath string
func closeClients(clients []*rpc.Client) {
for _, clnt := range clients {
clnt.Close()
}
}
// Same as SetNodes, but takes a path argument different from the package-level default.
func SetNodesWithPath(nodeList []string, path string) (err error) {
// Validate if number of nodes is within allowable range.
if n != 0 {
return errors.New("Cannot reinitialize dsync package")
} else if len(nodeList) < 4 {
return errors.New("Dsync not designed for less than 4 nodes")
} else if len(nodeList) > 16 {
return errors.New("Dsync not designed for more than 16 nodes")
}
nodes = make([]string, len(nodeList))
copy(nodes, nodeList[:])
rpcPath = path
n = len(nodes)
return nil
}