summaryrefslogtreecommitdiffstats
path: root/src/mds/SessionMap.h
blob: dd7721ccf4a076f510e473e6184c6370509c2d24 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
// vim: ts=8 sw=2 smarttab
/*
 * Ceph - scalable distributed file system
 *
 * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
 *
 * This is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 2.1, as published by the Free Software 
 * Foundation.  See file COPYING.
 * 
 */

#ifndef CEPH_MDS_SESSIONMAP_H
#define CEPH_MDS_SESSIONMAP_H

#include <set>
using std::set;

#include "include/unordered_map.h"

#include "include/Context.h"
#include "include/xlist.h"
#include "include/elist.h"
#include "include/interval_set.h"
#include "mdstypes.h"
#include "mds/MDSAuthCaps.h"
#include "common/perf_counters.h"
#include "common/DecayCounter.h"

class CInode;
struct MDRequestImpl;

#include "CInode.h"
#include "Capability.h"
#include "MDSContext.h"
#include "msg/Message.h"

enum {
  l_mdssm_first = 5500,
  l_mdssm_session_count,
  l_mdssm_session_add,
  l_mdssm_session_remove,
  l_mdssm_session_open,
  l_mdssm_session_stale,
  l_mdssm_total_load,
  l_mdssm_avg_load,
  l_mdssm_avg_session_uptime,
  l_mdssm_last,
};

/* 
 * session
 */

class Session : public RefCountedObject {
  // -- state etc --
public:
  /*
                    
        <deleted> <-- closed <------------+
             ^         |                  |
             |         v                  |
          killing <-- opening <----+      |
             ^         |           |      |
             |         v           |      |
           stale <--> open --> closing ---+

    + additional dimension of 'importing' (with counter)

  */

  using clock = ceph::coarse_mono_clock;
  using time = ceph::coarse_mono_time;


  enum {
    STATE_CLOSED = 0,
    STATE_OPENING = 1,   // journaling open
    STATE_OPEN = 2,
    STATE_CLOSING = 3,   // journaling close
    STATE_STALE = 4,
    STATE_KILLING = 5
  };

  static std::string_view get_state_name(int s) {
    switch (s) {
    case STATE_CLOSED: return "closed";
    case STATE_OPENING: return "opening";
    case STATE_OPEN: return "open";
    case STATE_CLOSING: return "closing";
    case STATE_STALE: return "stale";
    case STATE_KILLING: return "killing";
    default: return "???";
    }
  }

  void dump(Formatter *f) const;

private:
  int state = STATE_CLOSED;
  bool reconnecting = false;
  uint64_t state_seq = 0;
  int importing_count = 0;
  friend class SessionMap;

  // Human (friendly) name is soft state generated from client metadata
  void _update_human_name();
  std::string human_name;

  // Versions in this session was projected: used to verify
  // that appropriate mark_dirty calls follow.
  std::deque<version_t> projected;

  // request load average for this session
  DecayCounter load_avg;

  // Ephemeral state for tracking progress of capability recalls
  // caps being recalled recently by this session; used for Beacon warnings
  DecayCounter recall_caps;
  // caps that have been released
  DecayCounter release_caps;
  // throttle on caps recalled
  DecayCounter recall_caps_throttle;
  // second order throttle that prevents recalling too quickly
  DecayCounter recall_caps_throttle2o;
  // New limit in SESSION_RECALL
  uint32_t recall_limit = 0;

  // session caps liveness
  DecayCounter session_cache_liveness;

  // cap acquisition via readdir
  DecayCounter cap_acquisition;

  // session start time -- used to track average session time
  // note that this is initialized in the constructor rather
  // than at the time of adding a session to the sessionmap
  // as journal replay of sessionmap will not call add_session().
  time birth_time;

public:
  Session *reclaiming_from = nullptr;

  void push_pv(version_t pv)
  {
    ceph_assert(projected.empty() || projected.back() != pv);
    projected.push_back(pv);
  }

  void pop_pv(version_t v)
  {
    ceph_assert(!projected.empty());
    ceph_assert(projected.front() == v);
    projected.pop_front();
  }

  int get_state() const { return state; }
  void set_state(int new_state)
  {
    if (state != new_state) {
      state = new_state;
      state_seq++;
    }
  }

  void set_reconnecting(bool s) { reconnecting = s; }

  void decode(bufferlist::const_iterator &p);
  template<typename T>
  void set_client_metadata(T&& meta)
  {
    info.client_metadata = std::forward<T>(meta);
    _update_human_name();
  }

  const std::string& get_human_name() const {return human_name;}

  session_info_t info;                         ///< durable bits

  MDSAuthCaps auth_caps;

protected:
  ConnectionRef connection;
public:
  xlist<Session*>::item item_session_list;

  list<Message::ref> preopen_out_queue;  ///< messages for client, queued before they connect

  /* This is mutable to allow get_request_count to be const. elist does not
   * support const iterators yet.
   */
  mutable elist<MDRequestImpl*> requests;
  size_t get_request_count() const;

  interval_set<inodeno_t> pending_prealloc_inos; // journaling prealloc, will be added to prealloc_inos

  void notify_cap_release(size_t n_caps);
  uint64_t notify_recall_sent(size_t new_limit);
  auto get_recall_caps_throttle() const {
    return recall_caps_throttle.get();
  }
  auto get_recall_caps_throttle2o() const {
    return recall_caps_throttle2o.get();
  }
  auto get_recall_caps() const {
    return recall_caps.get();
  }
  auto get_release_caps() const {
    return release_caps.get();
  }
  auto get_session_cache_liveness() const {
    return session_cache_liveness.get();
  }
  auto get_cap_acquisition() const {
    return cap_acquisition.get();
  }

  inodeno_t next_ino() const {
    if (info.prealloc_inos.empty())
      return 0;
    return info.prealloc_inos.range_start();
  }
  inodeno_t take_ino(inodeno_t ino = 0) {
    ceph_assert(!info.prealloc_inos.empty());

    if (ino) {
      if (info.prealloc_inos.contains(ino))
	info.prealloc_inos.erase(ino);
      else
	ino = 0;
    }
    if (!ino) {
      ino = info.prealloc_inos.range_start();
      info.prealloc_inos.erase(ino);
    }
    info.used_inos.insert(ino, 1);
    return ino;
  }
  int get_num_projected_prealloc_inos() const {
    return info.prealloc_inos.size() + pending_prealloc_inos.size();
  }

  client_t get_client() const {
    return info.get_client();
  }

  std::string_view get_state_name() const { return get_state_name(state); }
  uint64_t get_state_seq() const { return state_seq; }
  bool is_closed() const { return state == STATE_CLOSED; }
  bool is_opening() const { return state == STATE_OPENING; }
  bool is_open() const { return state == STATE_OPEN; }
  bool is_closing() const { return state == STATE_CLOSING; }
  bool is_stale() const { return state == STATE_STALE; }
  bool is_killing() const { return state == STATE_KILLING; }

  void inc_importing() {
    ++importing_count;
  }
  void dec_importing() {
    ceph_assert(importing_count > 0);
    --importing_count;
  }
  bool is_importing() const { return importing_count > 0; }

  void set_load_avg_decay_rate(double rate) {
    ceph_assert(is_open() || is_stale());
    load_avg = DecayCounter(rate);
  }
  uint64_t get_load_avg() const {
    return (uint64_t)load_avg.get();
  }
  void hit_session() {
    load_avg.adjust();
  }

  double get_session_uptime() const {
    chrono::duration<double> uptime = clock::now() - birth_time;
    return uptime.count();
  }

  time get_birth_time() const {
    return birth_time;
  }

  // -- caps --
private:
  uint32_t cap_gen = 0;
  version_t cap_push_seq = 0;        // cap push seq #
  map<version_t, MDSContext::vec > waitfor_flush; // flush session messages

public:
  xlist<Capability*> caps;     // inodes with caps; front=most recently used
  xlist<ClientLease*> leases;  // metadata leases to clients
  time last_cap_renew = clock::zero();
  time last_seen = clock::zero();

  void inc_cap_gen() { ++cap_gen; }
  uint32_t get_cap_gen() const { return cap_gen; }

  version_t inc_push_seq() { return ++cap_push_seq; }
  version_t get_push_seq() const { return cap_push_seq; }

  version_t wait_for_flush(MDSContext* c) {
    waitfor_flush[get_push_seq()].push_back(c);
    return get_push_seq();
  }
  void finish_flush(version_t seq, MDSContext::vec& ls) {
    while (!waitfor_flush.empty()) {
      auto it = waitfor_flush.begin();
      if (it->first > seq)
	break;
      auto& v = it->second;
      ls.insert(ls.end(), v.begin(), v.end());
      waitfor_flush.erase(it);
    }
  }

  void touch_readdir_cap(uint32_t count) {
    cap_acquisition.hit(count);
  }

  void touch_cap(Capability *cap) {
    session_cache_liveness.hit(1.0);
    caps.push_front(&cap->item_session_caps);
  }

  void touch_cap_bottom(Capability *cap) {
    session_cache_liveness.hit(1.0);
    caps.push_back(&cap->item_session_caps);
  }

  void touch_lease(ClientLease *r) {
    session_cache_liveness.hit(1.0);
    leases.push_back(&r->item_session_lease);
  }

  bool is_any_flush_waiter() {
    return !waitfor_flush.empty();
  }

  // -- leases --
  uint32_t lease_seq = 0;

  // -- completed requests --
private:
  // Has completed_requests been modified since the last time we
  // wrote this session out?
  bool completed_requests_dirty = false;

  unsigned num_trim_flushes_warnings = 0;
  unsigned num_trim_requests_warnings = 0;
public:
  void add_completed_request(ceph_tid_t t, inodeno_t created) {
    info.completed_requests[t] = created;
    completed_requests_dirty = true;
  }
  bool trim_completed_requests(ceph_tid_t mintid) {
    // trim
    bool erased_any = false;
    while (!info.completed_requests.empty() && 
	   (mintid == 0 || info.completed_requests.begin()->first < mintid)) {
      info.completed_requests.erase(info.completed_requests.begin());
      erased_any = true;
    }

    if (erased_any) {
      completed_requests_dirty = true;
    }
    return erased_any;
  }
  bool have_completed_request(ceph_tid_t tid, inodeno_t *pcreated) const {
    map<ceph_tid_t,inodeno_t>::const_iterator p = info.completed_requests.find(tid);
    if (p == info.completed_requests.end())
      return false;
    if (pcreated)
      *pcreated = p->second;
    return true;
  }

  void add_completed_flush(ceph_tid_t tid) {
    info.completed_flushes.insert(tid);
  }
  bool trim_completed_flushes(ceph_tid_t mintid) {
    bool erased_any = false;
    while (!info.completed_flushes.empty() &&
	(mintid == 0 || *info.completed_flushes.begin() < mintid)) {
      info.completed_flushes.erase(info.completed_flushes.begin());
      erased_any = true;
    }
    if (erased_any) {
      completed_requests_dirty = true;
    }
    return erased_any;
  }
  bool have_completed_flush(ceph_tid_t tid) const {
    return info.completed_flushes.count(tid);
  }

  uint64_t get_num_caps() const {
    return caps.size();
  }

  unsigned get_num_completed_flushes() const { return info.completed_flushes.size(); }
  unsigned get_num_trim_flushes_warnings() const {
    return num_trim_flushes_warnings;
  }
  void inc_num_trim_flushes_warnings() { ++num_trim_flushes_warnings; }
  void reset_num_trim_flushes_warnings() { num_trim_flushes_warnings = 0; }

  unsigned get_num_completed_requests() const { return info.completed_requests.size(); }
  unsigned get_num_trim_requests_warnings() const {
    return num_trim_requests_warnings;
  }
  void inc_num_trim_requests_warnings() { ++num_trim_requests_warnings; }
  void reset_num_trim_requests_warnings() { num_trim_requests_warnings = 0; }

  bool has_dirty_completed_requests() const
  {
    return completed_requests_dirty;
  }

  void clear_dirty_completed_requests()
  {
    completed_requests_dirty = false;
  }

  int check_access(CInode *in, unsigned mask, int caller_uid, int caller_gid,
		   const vector<uint64_t> *gid_list, int new_uid, int new_gid);

  Session() = delete;
  Session(ConnectionRef con) :
    recall_caps(g_conf().get_val<double>("mds_recall_warning_decay_rate")),
    release_caps(g_conf().get_val<double>("mds_recall_warning_decay_rate")),
    recall_caps_throttle(g_conf().get_val<double>("mds_recall_max_decay_rate")),
    recall_caps_throttle2o(0.5),
    session_cache_liveness(g_conf().get_val<double>("mds_session_cache_liveness_decay_rate")),
    cap_acquisition(g_conf().get_val<double>("mds_session_cap_acquisition_decay_rate")),
    birth_time(clock::now()),
    auth_caps(g_ceph_context),
    item_session_list(this),
    requests(member_offset(MDRequestImpl, item_session_request))
  {
    set_connection(std::move(con));
  }
  ~Session() override {
    if (state == STATE_CLOSED) {
      item_session_list.remove_myself();
    } else {
      ceph_assert(!item_session_list.is_on_list());
    }
    preopen_out_queue.clear();
  }

  void set_connection(ConnectionRef con) {
    connection = std::move(con);
    auto& c = connection;
    if (c) {
      info.auth_name = c->get_peer_entity_name();
      info.inst.addr = c->get_peer_socket_addr();
      info.inst.name = entity_name_t(c->get_peer_type(), c->get_peer_global_id());
    }
  }
  const ConnectionRef& get_connection() const {
    return connection;
  }

  void clear() {
    pending_prealloc_inos.clear();
    info.clear_meta();

    cap_push_seq = 0;
    last_cap_renew = clock::zero();
  }
};

class SessionFilter
{
protected:
  // First is whether to filter, second is filter value
  std::pair<bool, bool> reconnecting;

public:
  std::map<std::string, std::string> metadata;
  std::string auth_name;
  std::string state;
  int64_t id;

  SessionFilter()
    : reconnecting(false, false), id(0)
  {}

  bool match(
      const Session &session,
      std::function<bool(client_t)> is_reconnecting) const;
  int parse(const std::vector<std::string> &args, std::stringstream *ss);
  void set_reconnecting(bool v)
  {
    reconnecting.first = true;
    reconnecting.second = v;
  }
};

/*
 * session map
 */

class MDSRank;

/**
 * Encapsulate the serialized state associated with SessionMap.  Allows
 * encode/decode outside of live MDS instance.
 */
class SessionMapStore {
public:
  using clock = Session::clock;
  using time = Session::time;

protected:
  version_t version;
  ceph::unordered_map<entity_name_t, Session*> session_map;
  PerfCounters *logger;

  // total request load avg
  double decay_rate;
  DecayCounter total_load_avg;

public:
  mds_rank_t rank;

  version_t get_version() const {return version;}

  virtual void encode_header(bufferlist *header_bl);
  virtual void decode_header(bufferlist &header_bl);
  virtual void decode_values(std::map<std::string, bufferlist> &session_vals);
  virtual void decode_legacy(bufferlist::const_iterator& blp);
  void dump(Formatter *f) const;

  void set_rank(mds_rank_t r)
  {
    rank = r;
  }

  Session* get_or_add_session(const entity_inst_t& i) {
    Session *s;
    auto session_map_entry = session_map.find(i.name);
    if (session_map_entry != session_map.end()) {
      s = session_map_entry->second;
    } else {
      s = session_map[i.name] = new Session(ConnectionRef());
      s->info.inst = i;
      s->last_cap_renew = Session::clock::now();
      if (logger) {
        logger->set(l_mdssm_session_count, session_map.size());
        logger->inc(l_mdssm_session_add);
      }
    }

    return s;
  }

  static void generate_test_instances(list<SessionMapStore*>& ls);

  void reset_state()
  {
    session_map.clear();
  }

  SessionMapStore()
    : version(0), logger(nullptr),
      decay_rate(g_conf().get_val<double>("mds_request_load_average_decay_rate")),
      total_load_avg(decay_rate), rank(MDS_RANK_NONE) {
  }
  virtual ~SessionMapStore() {};
};

class SessionMap : public SessionMapStore {
public:
  MDSRank *mds;

protected:
  version_t projected = 0, committing = 0, committed = 0;
public:
  map<int,xlist<Session*>* > by_state;
  uint64_t set_state(Session *session, int state);
  map<version_t, MDSContext::vec > commit_waiters;
  void update_average_session_age();

  SessionMap() = delete;
  explicit SessionMap(MDSRank *m) : mds(m) {}

  ~SessionMap() override
  {
    for (auto p : by_state)
      delete p.second;

    if (logger) {
      g_ceph_context->get_perfcounters_collection()->remove(logger);
    }

    delete logger;
  }

  void register_perfcounters();

  void set_version(const version_t v)
  {
    version = projected = v;
  }

  void set_projected(const version_t v)
  {
    projected = v;
  }

  version_t get_projected() const
  {
    return projected;
  }

  version_t get_committed() const
  {
    return committed;
  }

  version_t get_committing() const
  {
    return committing;
  }

  // sessions
  void decode_legacy(bufferlist::const_iterator& blp) override;
  bool empty() const { return session_map.empty(); }
  const auto& get_sessions() const {
    return session_map;
  }

  bool is_any_state(int state) const {
    auto it = by_state.find(state);
    if (it == by_state.end() || it->second->empty())
      return false;
    return true;
  }

  bool have_unclosed_sessions() const {
    return
      is_any_state(Session::STATE_OPENING) ||
      is_any_state(Session::STATE_OPEN) ||
      is_any_state(Session::STATE_CLOSING) ||
      is_any_state(Session::STATE_STALE) ||
      is_any_state(Session::STATE_KILLING);
  }
  bool have_session(entity_name_t w) const {
    return session_map.count(w);
  }
  Session* get_session(entity_name_t w) {
    auto session_map_entry = session_map.find(w);
    return (session_map_entry != session_map.end() ?
	    session_map_entry-> second : nullptr);
  }
  const Session* get_session(entity_name_t w) const {
    ceph::unordered_map<entity_name_t, Session*>::const_iterator p = session_map.find(w);
    if (p == session_map.end()) {
      return NULL;
    } else {
      return p->second;
    }
  }

  void add_session(Session *s);
  void remove_session(Session *s);
  void touch_session(Session *session);

  Session *get_oldest_session(int state) {
    auto by_state_entry = by_state.find(state);
    if (by_state_entry == by_state.end() || by_state_entry->second->empty())
      return 0;
    return by_state_entry->second->front();
  }

  void dump();

  template<typename F>
  void get_client_sessions(F&& f) const {
    for (const auto& p : session_map) {
      auto& session = p.second;
      if (session->info.inst.name.is_client())
	f(session);
    }
  }
  template<typename C>
  void get_client_session_set(C& c) const {
    auto f = [&c](auto& s) {
      c.insert(s);
    };
    get_client_sessions(f);
  }

  // helpers
  entity_inst_t& get_inst(entity_name_t w) {
    ceph_assert(session_map.count(w));
    return session_map[w]->info.inst;
  }
  version_t get_push_seq(client_t client) {
    return get_session(entity_name_t::CLIENT(client.v))->get_push_seq();
  }
  bool have_completed_request(metareqid_t rid) {
    Session *session = get_session(rid.name);
    return session && session->have_completed_request(rid.tid, NULL);
  }
  void trim_completed_requests(entity_name_t c, ceph_tid_t tid) {
    Session *session = get_session(c);
    ceph_assert(session);
    session->trim_completed_requests(tid);
  }

  void wipe();
  void wipe_ino_prealloc();

  // -- loading, saving --
  inodeno_t ino;
  MDSContext::vec waiting_for_load;

  object_t get_object_name() const;

  void load(MDSContext *onload);
  void _load_finish(
      int operation_r,
      int header_r,
      int values_r,
      bool first,
      bufferlist &header_bl,
      std::map<std::string, bufferlist> &session_vals,
      bool more_session_vals);

  void load_legacy();
  void _load_legacy_finish(int r, bufferlist &bl);

  void save(MDSContext *onsave, version_t needv=0);
  void _save_finish(version_t v);

protected:
  std::set<entity_name_t> dirty_sessions;
  std::set<entity_name_t> null_sessions;
  bool loaded_legacy = false;
  void _mark_dirty(Session *session, bool may_save);
public:

  /**
   * Advance the version, and mark this session
   * as dirty within the new version.
   *
   * Dirty means journalled but needing writeback
   * to the backing store.  Must have called
   * mark_projected previously for this session.
   */
  void mark_dirty(Session *session, bool may_save=true);

  /**
   * Advance the projected version, and mark this
   * session as projected within the new version
   *
   * Projected means the session is updated in memory
   * but we're waiting for the journal write of the update
   * to finish.  Must subsequently call mark_dirty
   * for sessions in the same global order as calls
   * to mark_projected.
   */
  version_t mark_projected(Session *session);

  /**
   * During replay, advance versions to account
   * for a session modification, and mark the
   * session dirty.
   */
  void replay_dirty_session(Session *session);

  /**
   * During replay, if a session no longer present
   * would have consumed a version, advance `version`
   * and `projected` to account for that.
   */
  void replay_advance_version();

  /**
   * During replay, open sessions, advance versions and
   * mark these sessions as dirty.
   */
  void replay_open_sessions(version_t event_cmapv,
			    map<client_t,entity_inst_t>& client_map,
			    map<client_t,client_metadata_t>& client_metadata_map);

  /**
   * For these session IDs, if a session exists with this ID, and it has
   * dirty completed_requests, then persist it immediately
   * (ahead of usual project/dirty versioned writes
   *  of the map).
   */
  void save_if_dirty(const std::set<entity_name_t> &tgt_sessions,
                     MDSGatherBuilder *gather_bld);

private:
  time avg_birth_time = clock::zero();

  uint64_t get_session_count_in_state(int state) {
    return !is_any_state(state) ? 0 : by_state[state]->size();
  }

  void update_average_birth_time(const Session &s, bool added=true) {
    uint32_t sessions = session_map.size();
    time birth_time = s.get_birth_time();

    if (sessions == 1) {
      avg_birth_time = added ? birth_time : clock::zero();
      return;
    }

    if (added) {
      avg_birth_time = clock::time_point(
        ((avg_birth_time - clock::zero()) / sessions) * (sessions - 1) +
        (birth_time - clock::zero()) / sessions);
    } else {
      avg_birth_time = clock::time_point(
        ((avg_birth_time - clock::zero()) / (sessions - 1)) * sessions -
        (birth_time - clock::zero()) / (sessions - 1));
    }
  }

public:
  void hit_session(Session *session);
  void handle_conf_change(const std::set <std::string> &changed);
};

std::ostream& operator<<(std::ostream &out, const Session &s);


#endif