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XL: listOnlineDisks should use modTime instead of version. (#2166) 

This change is needed to make reading from objects future proof
in-terms of handling online disks. Our current counter is not
based on affirmative knowledge and relies on arithmetic sequence
which can lead to bugs.

Using modTime simplifies the understanding of `xl.json` and future
tooling / debugging of the format.
This commit is contained in:
Harshavardhana 2016-07-12 15:20:31 -07:00 committed by Anand Babu (AB) Periasamy
parent e5cd35aad0
commit 623e0f9243
7 changed files with 158 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
docs/backend/xl/xl.json
View File

@ -42,7 +42,6 @@
],
},
"stat": {
"version": 0,
"modTime": "2016-05-24T00:09:40.122390255Z",
"size": 14824084
},

85
xl-v1-healing.go
View File

@ -16,33 +16,65 @@
package main
import "sync"
import (
"sync"
"time"
)
// Get the highest integer from a given integer slice.
func highestInt(intSlice []int64, highestInt int64) (highestInteger int64) {
highestInteger = highestInt
for _, integer := range intSlice {
if highestInteger < integer {
highestInteger = integer
break
// commonTime returns a maximally occurring time from a list of time.
func commonTime(modTimes []time.Time) (modTime time.Time) {
var maxima int // Counter for remembering max occurrence of elements.
timeOccurenceMap := make(map[time.Time]int)
// Ignore the uuid sentinel and count the rest.
for _, time := range modTimes {
if time == timeSentinel {
continue
}
timeOccurenceMap[time]++
}
// Find the common cardinality from previously collected
// occurrences of elements.
for time, count := range timeOccurenceMap {
if count > maxima {
maxima = count
modTime = time
}
}
return highestInteger
// Return the collected common uuid.
return modTime
}
// Extracts objects versions from xlMetaV1 slice and returns version slice.
func listObjectVersions(partsMetadata []xlMetaV1, errs []error) (versions []int64) {
versions = make([]int64, len(partsMetadata))
var timeSentinel = time.Unix(0, 0).UTC()
// Boot uuids upto disk count, setting the value to UUID sentinel.
func bootModtimes(diskCount int) []time.Time {
modTimes := make([]time.Time, diskCount)
// Boots up all the uuids.
for i := range modTimes {
modTimes[i] = timeSentinel
}
return modTimes
}
// Extracts list of times from xlMetaV1 slice and returns, skips
// slice elements which have errors. As a special error
// errFileNotFound is treated as a initial good condition.
func listObjectModtimes(partsMetadata []xlMetaV1, errs []error) (modTimes []time.Time) {
modTimes = bootModtimes(len(partsMetadata))
// Set a new time value, specifically set when
// error == errFileNotFound (this is needed when this is a
// fresh PutObject).
timeNow := time.Now().UTC()
for index, metadata := range partsMetadata {
if errs[index] == nil {
versions[index] = metadata.Stat.Version
// Once the file is found, save the uuid saved on disk.
modTimes[index] = metadata.Stat.ModTime
} else if errs[index] == errFileNotFound {
versions[index] = 1
} else {
versions[index] = -1
// Once the file is not found then the epoch is current time.
modTimes[index] = timeNow
}
}
return versions
return modTimes
}
// Reads all `xl.json` metadata as a xlMetaV1 slice.
@ -100,23 +132,22 @@ func (xl xlObjects) shouldHeal(onlineDisks []StorageAPI) (heal bool) {
// - slice returing readable disks.
// - xlMetaV1
// - bool value indicating if healing is needed.
// - error if any.
func (xl xlObjects) listOnlineDisks(partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, version int64, err error) {
func (xl xlObjects) listOnlineDisks(partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, modTime time.Time) {
onlineDisks = make([]StorageAPI, len(xl.storageDisks))
// List all the file versions from partsMetadata list.
versions := listObjectVersions(partsMetadata, errs)
// List all the file commit ids from parts metadata.
modTimes := listObjectModtimes(partsMetadata, errs)
// Get highest object version.
highestVersion := highestInt(versions, int64(1))
// Reduce list of UUIDs to a single common value.
modTime = commonTime(modTimes)
// Pick online disks with version set to highestVersion.
for index, version := range versions {
if version == highestVersion {
// Create a new online disks slice, which have common uuid.
for index, t := range modTimes {
if t == modTime {
onlineDisks[index] = xl.storageDisks[index]
} else {
onlineDisks[index] = nil
}
}
return onlineDisks, highestVersion, nil
return onlineDisks, modTime
}

83
xl-v1-healing_test.go Normal file
View File

@ -0,0 +1,83 @@
/*
* 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 main
import (
"testing"
"time"
)
// validates functionality provided to find most common
// time occurrence from a list of time.
func TestCommonTime(t *testing.T) {
// List of test cases for common modTime.
testCases := []struct {
times []time.Time
time time.Time
}{
{
// 1. Tests common times when slice has varying time elements.
[]time.Time{
time.Unix(0, 1).UTC(),
time.Unix(0, 2).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 2).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 1).UTC(),
}, time.Unix(0, 3).UTC(),
},
{
// 2. Tests common time obtained when all elements are equal.
[]time.Time{
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
}, time.Unix(0, 3).UTC(),
},
{
// 3. Tests common time obtained when elements have a mixture
// of sentinel values.
[]time.Time{
time.Unix(0, 3).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 2).UTC(),
time.Unix(0, 1).UTC(),
time.Unix(0, 3).UTC(),
time.Unix(0, 4).UTC(),
time.Unix(0, 3).UTC(),
timeSentinel,
timeSentinel,
timeSentinel,
}, time.Unix(0, 3).UTC(),
},
}
// Tests all the testcases, and validates them against expected
// common modtime. Tests fail if modtime does not match.
for i, testCase := range testCases {
// Obtain a common mod time from modTimes slice.
ctime := commonTime(testCase.times)
if testCase.time != ctime {
t.Fatalf("Test case %d, expect to pass but failed. Wanted modTime: %s, got modTime: %s\n", i+1, testCase.time, ctime)
}
}
}

1
xl-v1-metadata.go
View File

@ -87,7 +87,6 @@ func pickValidErasureInfo(eInfos []erasureInfo) erasureInfo {
type statInfo struct {
Size int64 `json:"size"` // Size of the object `xl.json`.
ModTime time.Time `json:"modTime"` // ModTime of the object `xl.json`.
Version int64 `json:"version"` // Version of the object `xl.json`, useful to calculate quorum.
}
// A xlMetaV1 represents `xl.json` metadata header.

28
xl-v1-multipart.go
View File

@ -266,7 +266,6 @@ func (xl xlObjects) newMultipartUpload(bucket string, object string, meta map[st
meta["content-type"] = contentType
}
xlMeta.Stat.ModTime = time.Now().UTC()
xlMeta.Stat.Version = 1
xlMeta.Meta = meta
// This lock needs to be held for any changes to the directory contents of ".minio/multipart/object/"
@ -355,13 +354,14 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
nsMutex.RUnlock(minioMetaBucket, uploadIDPath)
// List all online disks.
onlineDisks, _, err := xl.listOnlineDisks(partsMetadata, errs)
if err != nil {
return "", toObjectErr(err, bucket, object)
}
onlineDisks, _ := xl.listOnlineDisks(partsMetadata, errs)
// Pick one from the first valid metadata.
xlMeta := pickValidXLMeta(partsMetadata)
// Need a unique name for the part being written in minioMetaBucket to
// accommodate concurrent PutObjectPart requests
partSuffix := fmt.Sprintf("part.%d", partID)
tmpSuffix := getUUID()
tmpPartPath := path.Join(tmpMetaPrefix, tmpSuffix)
@ -434,8 +434,7 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
}
// Read metadata (again) associated with the object from all disks.
partsMetadata, errs = readAllXLMetadata(onlineDisks, minioMetaBucket,
uploadIDPath)
partsMetadata, errs = readAllXLMetadata(onlineDisks, minioMetaBucket, uploadIDPath)
if !isQuorum(errs, xl.writeQuorum) {
return "", toObjectErr(errXLWriteQuorum, bucket, object)
}
@ -448,7 +447,6 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
var checksums []checkSumInfo
for index, eInfo := range newEInfos {
if eInfo.IsValid() {
// Use a map to find union of checksums of parts that
// we concurrently written and committed before this
// part. N B For a different, concurrent upload of the
@ -474,21 +472,13 @@ func (xl xlObjects) PutObjectPart(bucket, object, uploadID string, partID int, s
}
// Pick one from the first valid metadata.
xlMeta := pickValidXLMeta(partsMetadata)
xlMeta = pickValidXLMeta(partsMetadata)
// Get current highest version based on re-read partsMetadata.
_, higherVersion, err := xl.listOnlineDisks(partsMetadata, errs)
if err != nil {
return "", toObjectErr(err, bucket, object)
}
// Increment version only if we have online disks less than configured storage disks.
if diskCount(onlineDisks) < len(xl.storageDisks) {
higherVersion++
}
onlineDisks, _ = xl.listOnlineDisks(partsMetadata, errs)
// Once part is successfully committed, proceed with updating XL metadata.
xlMeta.Stat.Version = higherVersion
xlMeta.Stat.ModTime = time.Now().UTC()
// Add the current part.
xlMeta.AddObjectPart(partID, partSuffix, newMD5Hex, size)

19
xl-v1-object.go
View File

@ -73,15 +73,12 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
}
// List all online disks.
onlineDisks, highestVersion, err := xl.listOnlineDisks(metaArr, errs)
if err != nil {
return toObjectErr(err, bucket, object)
}
onlineDisks, modTime := xl.listOnlineDisks(metaArr, errs)
// Pick latest valid metadata.
var xlMeta xlMetaV1
for _, meta := range metaArr {
if meta.IsValid() && meta.Stat.Version == highestVersion {
if meta.IsValid() && meta.Stat.ModTime == modTime {
xlMeta = meta
break
}
@ -386,15 +383,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
}
// List all online disks.
onlineDisks, higherVersion, err := xl.listOnlineDisks(partsMetadata, errs)
if err != nil {
return "", toObjectErr(err, bucket, object)
}
// Increment version only if we have online disks less than configured storage disks.
if diskCount(onlineDisks) < len(xl.storageDisks) {
higherVersion++
}
onlineDisks, _ := xl.listOnlineDisks(partsMetadata, errs)
var mw io.Writer
// Initialize md5 writer.
@ -513,7 +502,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
xlMeta.Meta = metadata
xlMeta.Stat.Size = size
xlMeta.Stat.ModTime = modTime
xlMeta.Stat.Version = higherVersion
// Add the final part.
xlMeta.AddObjectPart(1, "part.1", newMD5Hex, xlMeta.Stat.Size)

8
xl-v1-utils.go
View File

@ -78,14 +78,14 @@ func reduceErrs(errs []error) error {
// Validates if we have quorum based on the errors with errDiskNotFound.
func isQuorum(errs []error, minQuorumCount int) bool {
var diskFoundCount int
var errCount int
for _, err := range errs {
if err == errDiskNotFound {
if err == errDiskNotFound || err == errFaultyDisk || err == errDiskAccessDenied {
continue
}
diskFoundCount++
errCount++
}
return diskFoundCount >= minQuorumCount
return errCount >= minQuorumCount
}
// Similar to 'len(slice)' but returns the actual elements count