From 48594617b521f8307e91f80530988c25dd739cfb Mon Sep 17 00:00:00 2001
From: Krishna Srinivas <634494+krishnasrinivas@users.noreply.github.com>
Date: Thu, 7 Apr 2022 23:19:13 -0700
Subject: [PATCH] Parallelize decommissioning process (#14704)

---
 cmd/erasure-server-pool-decom.go | 58 ++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 25 deletions(-)

diff --git a/cmd/erasure-server-pool-decom.go b/cmd/erasure-server-pool-decom.go
index e04eae03c..5b772c39e 100644
--- a/cmd/erasure-server-pool-decom.go
+++ b/cmd/erasure-server-pool-decom.go
@@ -24,12 +24,15 @@ import (
 	"fmt"
 	"net/http"
 	"sort"
+	"strconv"
+	"sync"
 	"time"
 
 	"github.com/dustin/go-humanize"
 	"github.com/minio/minio/internal/hash"
 	"github.com/minio/minio/internal/logger"
 	"github.com/minio/pkg/console"
+	"github.com/minio/pkg/env"
 )
 
 // PoolDecommissionInfo currently decommissioning information
@@ -578,15 +581,16 @@ func (v versionsSorter) reverse() {
 }
 
 func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool *erasureSets, bName string) error {
-	var forwardTo string
-	// If we resume to the same bucket, forward to last known item.
-	rbucket, robject := z.poolMeta.ResumeBucketObject(idx)
-	if rbucket != "" && rbucket == bName {
-		forwardTo = robject
-	}
+	var wg sync.WaitGroup
+	wStr := env.Get("_MINIO_DECOMMISSION_WORKERS", strconv.Itoa(len(pool.sets)))
+	workerSize, _ := strconv.Atoi(wStr)
+
+	parallelWorkers := make(chan struct{}, workerSize)
 
 	versioned := globalBucketVersioningSys.Enabled(bName)
 	for _, set := range pool.sets {
+		parallelWorkers <- struct{}{}
+		set := set
 		disks := set.getOnlineDisks()
 		if len(disks) == 0 {
 			logger.LogIf(GlobalContext, fmt.Errorf("no online disks found for set with endpoints %s",
@@ -698,26 +702,30 @@ func (z *erasureServerPools) decommissionPool(ctx context.Context, idx int, pool
 			bucket:    bName,
 		}
 
-		if err := listPathRaw(ctx, listPathRawOptions{
-			disks:          disks,
-			bucket:         bName,
-			recursive:      true,
-			forwardTo:      forwardTo,
-			minDisks:       len(disks) / 2, // to capture all quorum ratios
-			reportNotFound: false,
-			agreed:         decommissionEntry,
-			partial: func(entries metaCacheEntries, nAgreed int, errs []error) {
-				entry, ok := entries.resolve(&resolver)
-				if ok {
-					decommissionEntry(*entry)
-				}
-			},
-			finished: nil,
-		}); err != nil {
-			// Decommissioning failed and won't continue
-			return err
-		}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			err := listPathRaw(ctx, listPathRawOptions{
+				disks:          disks,
+				bucket:         bName,
+				recursive:      true,
+				forwardTo:      "",
+				minDisks:       len(disks) / 2, // to capture all quorum ratios
+				reportNotFound: false,
+				agreed:         decommissionEntry,
+				partial: func(entries metaCacheEntries, nAgreed int, errs []error) {
+					entry, ok := entries.resolve(&resolver)
+					if ok {
+						decommissionEntry(*entry)
+					}
+				},
+				finished: nil,
+			})
+			logger.LogIf(ctx, err)
+			<-parallelWorkers
+		}()
 	}
+	wg.Wait()
 	return nil
 }