minio/xl-v1-healing.go

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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 main
import (
"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
}
// Beginning of unix time is treated as sentinel value here.
var timeSentinel = time.Unix(0, 0).UTC()
// Boot modTimes up to disk count, setting the value to time sentinel.
func bootModtimes(diskCount int) []time.Time {
modTimes := make([]time.Time, diskCount)
// Boots up all the modtimes.
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
}
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.
// - modTime of the Object
func listOnlineDisks(disks []StorageAPI, partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, modTime time.Time) {
onlineDisks = make([]StorageAPI, len(disks))
// 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] = disks[index]
} else {
onlineDisks[index] = nil
}
}
return onlineDisks, modTime
}