minio/xl-v1-common.go
Harshavardhana a0635dcdd9 XL: Do not rely on getLoadBalancedQuorumDisks for NS consistency. (#2243)
The reason is any function relying on `getLoadBalancedQuorumDisks`
cannot possibly have an idempotent behavior.

The problem comes from given a set of N disks returning just a
shuffled N/2 disks.  In case of a scenario where we have N/2
number of failed disks, the returned value of `getLoadBalancedQuorumDisks`
is not equal to the same failed disks so essentially calls using such
disks might succeed or fail randomly at different intervals in time.

This proposal change is we move to `getLoadBalancedDisks()`
and use the shuffled N disks as a whole. Since most of the time we might
hit a good disk since we are not reducing our solution space. This
also provides consistent behavior for all the functions which rely
on shuffled disks.

Fixes #2242
2016-07-21 00:27:08 -07:00

72 lines
2.3 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 (
"path"
"time"
)
// getLoadBalancedDisks - fetches load balanced (sufficiently randomized) disk slice.
func (xl xlObjects) getLoadBalancedDisks() (disks []StorageAPI) {
// Based on the random shuffling return back randomized disks.
for _, i := range hashOrder(time.Now().UTC().String(), len(xl.storageDisks)) {
disks = append(disks, xl.storageDisks[i-1])
}
return disks
}
// This function does the following check, suppose
// object is "a/b/c/d", stat makes sure that objects ""a/b/c""
// "a/b" and "a" do not exist.
func (xl xlObjects) parentDirIsObject(bucket, parent string) bool {
var isParentDirObject func(string) bool
isParentDirObject = func(p string) bool {
if p == "." {
return false
}
if xl.isObject(bucket, p) {
// If there is already a file at prefix "p" return error.
return true
}
// Check if there is a file as one of the parent paths.
return isParentDirObject(path.Dir(p))
}
return isParentDirObject(parent)
}
// isObject - returns `true` if the prefix is an object i.e if
// `xl.json` exists at the leaf, false otherwise.
func (xl xlObjects) isObject(bucket, prefix string) (ok bool) {
for _, disk := range xl.getLoadBalancedDisks() {
if disk == nil {
continue
}
// Check if 'prefix' is an object on this 'disk', else continue the check the next disk
_, err := disk.StatFile(bucket, path.Join(prefix, xlMetaJSONFile))
if err == nil {
return true
}
// Ignore for file not found, disk not found or faulty disk.
if isErrIgnored(err, walkResultIgnoredErrs) {
continue
}
errorIf(err, "Unable to stat a file %s/%s/%s", bucket, prefix, xlMetaJSONFile)
} // Exhausted all disks - return false.
return false
}