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.
154 lines
4.6 KiB
Go
154 lines
4.6 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package main
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import (
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"sync"
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"time"
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)
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// commonTime returns a maximally occurring time from a list of time.
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func commonTime(modTimes []time.Time) (modTime time.Time) {
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var maxima int // Counter for remembering max occurrence of elements.
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timeOccurenceMap := make(map[time.Time]int)
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// Ignore the uuid sentinel and count the rest.
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for _, time := range modTimes {
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if time == timeSentinel {
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continue
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}
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timeOccurenceMap[time]++
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}
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// Find the common cardinality from previously collected
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// occurrences of elements.
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for time, count := range timeOccurenceMap {
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if count > maxima {
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maxima = count
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modTime = time
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}
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}
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// Return the collected common uuid.
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return modTime
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}
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var timeSentinel = time.Unix(0, 0).UTC()
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// Boot uuids upto disk count, setting the value to UUID sentinel.
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func bootModtimes(diskCount int) []time.Time {
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modTimes := make([]time.Time, diskCount)
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// Boots up all the uuids.
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for i := range modTimes {
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modTimes[i] = timeSentinel
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}
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return modTimes
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}
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// Extracts list of times from xlMetaV1 slice and returns, skips
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// slice elements which have errors. As a special error
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// errFileNotFound is treated as a initial good condition.
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func listObjectModtimes(partsMetadata []xlMetaV1, errs []error) (modTimes []time.Time) {
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modTimes = bootModtimes(len(partsMetadata))
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// Set a new time value, specifically set when
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// error == errFileNotFound (this is needed when this is a
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// fresh PutObject).
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timeNow := time.Now().UTC()
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for index, metadata := range partsMetadata {
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if errs[index] == nil {
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// Once the file is found, save the uuid saved on disk.
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modTimes[index] = metadata.Stat.ModTime
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} else if errs[index] == errFileNotFound {
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// Once the file is not found then the epoch is current time.
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modTimes[index] = timeNow
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}
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}
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return modTimes
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}
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// Reads all `xl.json` metadata as a xlMetaV1 slice.
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// Returns error slice indicating the failed metadata reads.
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func readAllXLMetadata(disks []StorageAPI, bucket, object string) ([]xlMetaV1, []error) {
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errs := make([]error, len(disks))
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metadataArray := make([]xlMetaV1, len(disks))
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var wg = &sync.WaitGroup{}
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// Read `xl.json` parallelly across disks.
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for index, disk := range disks {
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if disk == nil {
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errs[index] = errDiskNotFound
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continue
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}
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wg.Add(1)
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// Read `xl.json` in routine.
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go func(index int, disk StorageAPI) {
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defer wg.Done()
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var err error
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metadataArray[index], err = readXLMeta(disk, bucket, object)
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if err != nil {
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errs[index] = err
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return
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}
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}(index, disk)
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}
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// Wait for all the routines to finish.
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wg.Wait()
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// Return all the metadata.
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return metadataArray, errs
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}
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func (xl xlObjects) shouldHeal(onlineDisks []StorageAPI) (heal bool) {
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onlineDiskCount := diskCount(onlineDisks)
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// If online disks count is lesser than configured disks, most
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// probably we need to heal the file, additionally verify if the
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// count is lesser than readQuorum, if not we throw an error.
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if onlineDiskCount < len(xl.storageDisks) {
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// Online disks lesser than total storage disks, needs to be
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// healed. unless we do not have readQuorum.
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heal = true
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// Verify if online disks count are lesser than readQuorum
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// threshold, return an error.
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if onlineDiskCount < xl.readQuorum {
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errorIf(errXLReadQuorum, "Unable to establish read quorum, disks are offline.")
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return false
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}
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}
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return heal
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}
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// Returns slice of online disks needed.
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// - slice returing readable disks.
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// - xlMetaV1
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// - bool value indicating if healing is needed.
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func (xl xlObjects) listOnlineDisks(partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, modTime time.Time) {
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onlineDisks = make([]StorageAPI, len(xl.storageDisks))
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// List all the file commit ids from parts metadata.
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modTimes := listObjectModtimes(partsMetadata, errs)
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// Reduce list of UUIDs to a single common value.
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modTime = commonTime(modTimes)
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// Create a new online disks slice, which have common uuid.
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for index, t := range modTimes {
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if t == modTime {
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onlineDisks[index] = xl.storageDisks[index]
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} else {
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onlineDisks[index] = nil
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}
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}
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return onlineDisks, modTime
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}
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