minio/xl-v1-healing.go
Harshavardhana 623e0f9243 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.
2016-07-12 15:20:31 -07:00

154 lines
4.6 KiB
Go

/*
* 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 (
"sync"
"time"
)
// 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 the collected common uuid.
return modTime
}
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 {
// Once the file is found, save the uuid saved on disk.
modTimes[index] = metadata.Stat.ModTime
} else if errs[index] == errFileNotFound {
// Once the file is not found then the epoch is current time.
modTimes[index] = timeNow
}
}
return modTimes
}
// Reads all `xl.json` metadata as a xlMetaV1 slice.
// Returns error slice indicating the failed metadata reads.
func readAllXLMetadata(disks []StorageAPI, bucket, object string) ([]xlMetaV1, []error) {
errs := make([]error, len(disks))
metadataArray := make([]xlMetaV1, len(disks))
var wg = &sync.WaitGroup{}
// Read `xl.json` parallelly across disks.
for index, disk := range disks {
if disk == nil {
errs[index] = errDiskNotFound
continue
}
wg.Add(1)
// Read `xl.json` in routine.
go func(index int, disk StorageAPI) {
defer wg.Done()
var err error
metadataArray[index], err = readXLMeta(disk, bucket, object)
if err != nil {
errs[index] = err
return
}
}(index, disk)
}
// Wait for all the routines to finish.
wg.Wait()
// Return all the metadata.
return metadataArray, errs
}
func (xl xlObjects) shouldHeal(onlineDisks []StorageAPI) (heal bool) {
onlineDiskCount := diskCount(onlineDisks)
// If online disks count is lesser than configured disks, most
// probably we need to heal the file, additionally verify if the
// count is lesser than readQuorum, if not we throw an error.
if onlineDiskCount < len(xl.storageDisks) {
// Online disks lesser than total storage disks, needs to be
// healed. unless we do not have readQuorum.
heal = true
// Verify if online disks count are lesser than readQuorum
// threshold, return an error.
if onlineDiskCount < xl.readQuorum {
errorIf(errXLReadQuorum, "Unable to establish read quorum, disks are offline.")
return false
}
}
return heal
}
// Returns slice of online disks needed.
// - slice returing readable disks.
// - xlMetaV1
// - bool value indicating if healing is needed.
func (xl xlObjects) listOnlineDisks(partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, modTime time.Time) {
onlineDisks = make([]StorageAPI, len(xl.storageDisks))
// List all the file commit ids from parts metadata.
modTimes := listObjectModtimes(partsMetadata, errs)
// Reduce list of UUIDs to a single common value.
modTime = commonTime(modTimes)
// 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, modTime
}