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fix: improve node selection in sticky session #575

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fix: improve node selection in sticky session #575

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a57ab29
fix: improve node selection in sticky session
zghong Dec 7, 2025
6c7f437
fix: use the same hash value for both replica and host index calculation
zghong Dec 7, 2025
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42 changes: 22 additions & 20 deletions scope.go
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Original file line number Diff line number Diff line change
Expand Up @@ -58,9 +58,11 @@ type scope struct {
}

func newScope(req *http.Request, u *user, c *cluster, cu *clusterUser, sessionId string, sessionTimeout int) *scope {
h := c.getHost()
var h *topology.Node
if sessionId != "" {
h = c.getHostSticky(sessionId)
} else {
h = c.getHost()
}
var localAddr string
if addr, ok := req.Context().Value(http.LocalAddrContextKey).(net.Addr); ok {
Expand Down Expand Up @@ -874,27 +876,29 @@ func (c *cluster) getReplica() *replica {
return r
}

// getReplicaSticky returns replica by stickiness from the cluster.
//
// Always returns non-nil.
func (c *cluster) getReplicaSticky(sessionId string) *replica {
idx := atomic.AddUint32(&c.nextReplicaIdx, 1)
n := uint32(len(c.replicas))
if n == 1 {
return c.replicas[0]
}

idx %= n
// handling sticky session
idx := (hash(sessionId) >> 16) % n
r := c.replicas[idx]

for i := uint32(1); i < n; i++ {
// handling sticky session
sessionId := hash(sessionId)
tmpIdx := (sessionId) % n
// TODO: In principle, sticky session must always proxy to the fixed replica continuously,
// no matter whether the replica is active or not.
for i := range n {
tmpIdx := (idx + i) % n
tmpRSticky := c.replicas[tmpIdx]
log.Debugf("Sticky replica candidate is: %s", tmpRSticky.name)
if !tmpRSticky.isActive() {
log.Debugf("Sticky session replica has been picked up, but it is not available")
log.Errorf("Sticky replica candidate %q for session_id %q is inactive", tmpRSticky.name, sessionId)
continue
}
log.Debugf("Sticky session replica is: %s, session_id: %d, replica_idx: %d, max replicas in pool: %d", tmpRSticky.name, sessionId, tmpIdx, n)
log.Debugf("Sticky replica for session_id %q: %q", sessionId, tmpRSticky.name)
return tmpRSticky
}
// The returned replica may be inactive. This is OK,
Expand All @@ -907,27 +911,25 @@ func (c *cluster) getReplicaSticky(sessionId string) *replica {
//
// Always returns non-nil.
func (r *replica) getHostSticky(sessionId string) *topology.Node {
idx := atomic.AddUint32(&r.nextHostIdx, 1)
n := uint32(len(r.hosts))
if n == 1 {
return r.hosts[0]
}

idx %= n
// handling sticky session
idx := (hash(sessionId) & 0xFFFF) % n
h := r.hosts[idx]

// Scan all the hosts for the least loaded host.
for i := uint32(1); i < n; i++ {
// handling sticky session
sessionId := hash(sessionId)
tmpIdx := (sessionId) % n
// TODO: In principle, sticky session must always proxy to the fixed host continuously,
// no matter whether the host is active or not.
for i := range n {
tmpIdx := (idx + i) % n
tmpHSticky := r.hosts[tmpIdx]
log.Debugf("Sticky server candidate is: %s", tmpHSticky)
if !tmpHSticky.IsActive() {
log.Debugf("Sticky session server has been picked up, but it is not available")
log.Errorf("Sticky host candidate %q for session_id %q is inactive", tmpHSticky, sessionId)
continue
}
log.Debugf("Sticky session server is: %s, session_id: %d, server_idx: %d, max nodes in pool: %d", tmpHSticky, sessionId, tmpIdx, n)
log.Debugf("Sticky host for session_id %q: %q", sessionId, tmpHSticky)
return tmpHSticky
}

Expand Down
8 changes: 4 additions & 4 deletions scope_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -396,10 +396,10 @@ func TestDecorateRequest(t *testing.T) {

func TestGetHostSticky(t *testing.T) {
exceptedSessionHostMap := map[string]string{
"0": "127.0.0.22",
"0": "127.0.0.66",
"1": "127.0.0.33",
"2": "127.0.0.44",
"3": "127.0.0.55",
"3": "127.0.0.11",
}
c := testGetCluster()
for i := 0; i < 10000; i++ {
Expand All @@ -415,10 +415,10 @@ func TestIncQueued(t *testing.T) {
cu := testGetClusterUser()
c := testGetCluster()
expectedSessionHostMap := map[string]string{
"0": "127.0.0.22",
"0": "127.0.0.66",
"1": "127.0.0.33",
"2": "127.0.0.44",
"3": "127.0.0.55",
"3": "127.0.0.11",
}
if err := testConcurrentQuery(c, u, cu, 10000, expectedSessionHostMap); err != nil {
t.Fatalf("incQueue test err: %s", err)
Expand Down