From da40bd0960806df8e2799e4fb716d41ad08b169f Mon Sep 17 00:00:00 2001
From: Tom Clegg <tclegg@veritasgenetics.com>
Date: Wed, 6 Jun 2018 17:01:53 -0400
Subject: [PATCH] 13427: Use same index result N times if a device is mounted N
 times.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tclegg@veritasgenetics.com>
---
 services/keep-balance/balance.go | 62 +++++++++++++++++++++-----------
 1 file changed, 42 insertions(+), 20 deletions(-)

diff --git a/services/keep-balance/balance.go b/services/keep-balance/balance.go
index 328e623422..c7fa882303 100644
--- a/services/keep-balance/balance.go
+++ b/services/keep-balance/balance.go
@@ -274,32 +274,54 @@ func (bal *Balancer) GetCurrentState(c *arvados.Client, pageSize, bufs int) erro
 	errs := make(chan error, 2+len(bal.KeepServices))
 	wg := sync.WaitGroup{}
 
-	// Start one goroutine for each KeepService: retrieve the
-	// index, and add the returned blocks to BlockStateMap.
+	// When a device is mounted more than once, we will get its
+	// index only once, and call AddReplicas on all of the mounts.
+	// equivMount keys are the mounts that will be indexed, and
+	// each value is a list of mounts to apply the received index
+	// to.
+	equivMount := map[*KeepMount][]*KeepMount{}
+	// deviceMount maps each device ID to the one mount that will
+	// be indexed for that device.
+	deviceMount := map[string]*KeepMount{}
 	for _, srv := range bal.KeepServices {
+		for _, mnt := range srv.mounts {
+			equiv := deviceMount[mnt.DeviceID]
+			if equiv == nil {
+				equiv = mnt
+				if mnt.DeviceID != "" {
+					deviceMount[mnt.DeviceID] = equiv
+				}
+			}
+			equivMount[equiv] = append(equivMount[equiv], mnt)
+		}
+	}
+
+	// Start one goroutine for each (non-redundant) mount:
+	// retrieve the index, and add the returned blocks to
+	// BlockStateMap.
+	for _, mounts := range equivMount {
 		wg.Add(1)
-		go func(srv *KeepService) {
+		go func(mounts []*KeepMount) {
 			defer wg.Done()
-			bal.logf("%s: retrieve indexes", srv)
-			for _, mount := range srv.mounts {
-				bal.logf("%s: retrieve index", mount)
-				idx, err := srv.IndexMount(c, mount.UUID, "")
-				if err != nil {
-					errs <- fmt.Errorf("%s: retrieve index: %v", mount, err)
-					return
-				}
-				if len(errs) > 0 {
-					// Some other goroutine encountered an
-					// error -- any further effort here
-					// will be wasted.
-					return
-				}
+			bal.logf("mount %s: retrieve index from %s", mounts[0], mounts[0].KeepService)
+			idx, err := mounts[0].KeepService.IndexMount(c, mounts[0].UUID, "")
+			if err != nil {
+				errs <- fmt.Errorf("%s: retrieve index: %v", mounts[0], err)
+				return
+			}
+			if len(errs) > 0 {
+				// Some other goroutine encountered an
+				// error -- any further effort here
+				// will be wasted.
+				return
+			}
+			for _, mount := range mounts {
 				bal.logf("%s: add %d replicas to map", mount, len(idx))
 				bal.BlockStateMap.AddReplicas(mount, idx)
-				bal.logf("%s: done", mount)
+				bal.logf("%s: added %d replicas", mount, len(idx))
 			}
-			bal.logf("%s: done", srv)
-		}(srv)
+			bal.logf("mount %s: index done", mounts[0])
+		}(mounts)
 	}
 
 	// collQ buffers incoming collections so we can start fetching
-- 
2.30.2