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XL: Do not rely on getLoadBalancedQuorumDisks for NS consistency. (#2243)

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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
This commit is contained in:
Harshavardhana
2016-07-21 00:27:08 -07:00
committed by Anand Babu (AB) Periasamy
parent 41f4f2806d
commit a0635dcdd9
6 changed files with 57 additions and 47 deletions
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12
xl-v1-common.go
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@@ -21,15 +21,7 @@ import (
"time"
)
// getLoadBalancedQuorumDisks - fetches load balanced sufficiently
// randomized quorum disk slice.
func (xl xlObjects) getLoadBalancedQuorumDisks() (disks []StorageAPI) {
// It is okay to have readQuorum disks.
return xl.getLoadBalancedDisks()[0 : xl.readQuorum-1]
}
// getLoadBalancedDisks - fetches load balanced (sufficiently
// randomized) disk slice.
// 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)) {
@@ -60,7 +52,7 @@ func (xl xlObjects) parentDirIsObject(bucket, parent string) bool {
// 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.getLoadBalancedQuorumDisks() {
for _, disk := range xl.getLoadBalancedDisks() {
if disk == nil {
continue
}