GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2025-08-31 02:39:21
Exec Total Coverage
Lines: 260 263 98.9%
Branches: 89 110 80.9%
Line Branch Exec Source
1 /**
2 * This file is part of the CernVM File System.
3 */
4
5 #ifndef CVMFS_SMALLHASH_H_
6 #define CVMFS_SMALLHASH_H_
7
8 #ifndef __STDC_FORMAT_MACROS
9 // NOLINTNEXTLINE
10 #define __STDC_FORMAT_MACROS
11 #endif
12
13 #include "duplex_testing.h"
14 #include <inttypes.h>
15 #include <pthread.h>
16 #include <stdint.h>
17
18 #include <algorithm>
19 #include <cassert>
20 #include <cstdlib>
21 #include <new>
22
23 #include "util/atomic.h"
24 #include "util/murmur.hxx"
25 #include "util/prng.h"
26 #include "util/smalloc.h"
27
28 /**
29 * Hash table with linear probing as collision resolution. Works only for
30 * a fixed (maximum) number of elements, i.e. no resizing. Load factor fixed
31 * to 0.7.
32 */
33 template<class Key, class Value, class Derived>
34 class SmallHashBase {
35 FRIEND_TEST(T_Smallhash, InsertAndCopyMd5Slow);
36
37 public:
38 static const double kLoadFactor; // mainly useless for the dynamic version
39 static const double kThresholdGrow; // only used for resizable version
40 static const double kThresholdShrink; // only used for resizable version
41
42 113807 SmallHashBase() {
43 113807 keys_ = NULL;
44 113807 values_ = NULL;
45 113807 hasher_ = NULL;
46 113807 bytes_allocated_ = 0;
47 113807 num_collisions_ = 0;
48 113807 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 113807 capacity_ = 0;
52 113807 initial_capacity_ = 0;
53 113807 size_ = 0;
54 113807 }
55
56 113669 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 113799 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 113799 hasher_ = hasher;
61 113799 empty_key_ = empty;
62 113799 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 113799 / kLoadFactor);
64 113799 initial_capacity_ = capacity_;
65 113799 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 113799 AllocMemory();
67 113799 this->DoClear(false);
68 113799 }
69
70 28950611 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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 28950611 const bool found = DoLookup(key, &bucket, &collisions);
74
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 28999912 if (found)
75
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 19748764 *value = values_[bucket];
76 28999912 return found;
77 }
78
79 /**
80 * Returns both the key and the value. That is useful if Key's equality
81 * operator implements an equivalence relation on Key. In this case, LookupEx
82 * returns the key representing the equivalence class that has been used
83 * during Insert().
84 * Used to return a glue::InodeEx element when looking for an inode.
85 */
86 144 bool LookupEx(Key *key, Value *value) const {
87 144 uint32_t bucket = ScaleHash(*key);
88
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 144 while (!(keys_[bucket] == empty_key_)) {
89
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 96 if (keys_[bucket] == *key) {
90 96 *key = keys_[bucket];
91 96 *value = values_[bucket];
92 96 return true;
93 }
94 ✗ bucket = (bucket + 1) % capacity_;
95 }
96 48 return false;
97 }
98
99 11070267 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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 11070267 const bool found = DoLookup(key, &bucket, &collisions);
103 11070267 return found;
104 }
105
106 272394663 void Insert(const Key &key, const Value &value) {
107 272394663 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 271438791 const bool overwritten = DoInsert(key, value, true);
109 271054109 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 271054109 }
111
112 21322608 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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 21322608 const bool found = DoLookup(key, &bucket, &collisions);
116
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 20962978 if (found) {
117 20964728 keys_[bucket] = empty_key_;
118 20964728 size_--;
119 20964728 bucket = (bucket + 1) % capacity_;
120
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 58544415 while (!(keys_[bucket] == empty_key_)) {
121 37767971 Key rehash = keys_[bucket];
122 37767971 keys_[bucket] = empty_key_;
123
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 37767971 DoInsert(rehash, values_[bucket], false);
124 37579687 bucket = (bucket + 1) % capacity_;
125 }
126
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 20776444 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 21020518 return found;
129 }
130
131 324 void Clear() { DoClear(true); }
132
133 2671 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 441 static double GetEntrySize() {
135 882 const double unit = sizeof(Key) + sizeof(Value);
136 882 return unit / kLoadFactor;
137 }
138
139 void GetCollisionStats(uint64_t *num_collisions,
140 uint32_t *max_collisions) const {
141 *num_collisions = num_collisions_;
142 *max_collisions = max_collisions_;
143 }
144
145 // Careful with the direct access TODO: iterator
146 uint32_t capacity() const { return capacity_; }
147 295512 Key empty_key() const { return empty_key_; }
148 590394 Key *keys() const { return keys_; }
149 432 Value *values() const { return values_; }
150
151 // Only needed by compat
152 ✗ void SetHasher(uint32_t (*hasher)(const Key &key)) { hasher_ = hasher; }
153
154 protected:
155 417286037 uint32_t ScaleHash(const Key &key) const {
156 417286037 const double bucket = (static_cast<double>(hasher_(key))
157 416569039 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 416569039 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 134559 void AllocMemory() {
163 134559 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 134559 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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 670250210 for (uint32_t i = 0; i < capacity_; ++i) {
166 670115651 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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 670911874 for (uint32_t i = 0; i < capacity_; ++i) {
169 670791699 /*values_[i] =*/new (values_ + i) Value();
170 }
171 120175 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 120175 }
173
174 134429 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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 670783350 for (uint32_t i = 0; i < c; ++i) {
176 670648921 k[i].~Key();
177 }
178
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 670683326 for (uint32_t i = 0; i < c; ++i) {
179 670548897 v[i].~Value();
180 }
181
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 134429 if (k)
182 134421 smunmap(k);
183
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 134429 if (v)
184 134421 smunmap(v);
185 134429 k = NULL;
186 134429 v = NULL;
187 134429 }
188
189 // Returns true iff the key is overwritten
190 327775558 bool DoInsert(const Key &key, const Value &value,
191 const bool count_collisions) {
192 uint32_t bucket;
193 uint32_t collisions;
194
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 327775558 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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 327278226 if (count_collisions) {
196 271045227 num_collisions_ += collisions;
197 271045227 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 327328658 keys_[bucket] = key;
200
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 327328658 values_[bucket] = value;
201 327328658 return overwritten;
202 }
203
204 417129483 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 417129483 *bucket = ScaleHash(key);
206 416057360 *collisions = 0;
207
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 10472756018 while (!(keys_[*bucket] == empty_key_)) {
208
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 10147545029 if (keys_[*bucket] == key)
209 90846371 return true;
210 10056698658 *bucket = (*bucket + 1) % capacity_;
211 10056698658 (*collisions)++;
212 }
213 325210989 return false;
214 }
215
216 134595 void DoClear(const bool reset_capacity) {
217
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 134595 if (reset_capacity)
218 544 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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 671011506 for (uint32_t i = 0; i < capacity_; ++i)
220 670876911 keys_[i] = empty_key_;
221 134595 size_ = 0;
222 134595 }
223
224 // Methods for resizable version
225 void SetThresholds() { }
226 void Grow() { }
227 void Shrink() { }
228 void ResetCapacity() { }
229
230 // Separate key and value arrays for better locality
231 Key *keys_;
232 Value *values_;
233 uint32_t capacity_;
234 uint32_t initial_capacity_;
235 uint32_t size_;
236 uint32_t (*hasher_)(const Key &key);
237 uint64_t bytes_allocated_;
238 uint64_t num_collisions_;
239 uint32_t max_collisions_; /**< maximum collisions for a single insert */
240 Key empty_key_;
241 };
242
243
244 template<class Key, class Value>
245 class SmallHashFixed
246 : public SmallHashBase<Key, Value, SmallHashFixed<Key, Value> > {
247 friend class SmallHashBase<Key, Value, SmallHashFixed<Key, Value> >;
248
249 protected:
250 // No-ops
251 2635 void SetThresholds() { }
252 147543 void Grow() { }
253 22984 void Shrink() { }
254 36 void ResetCapacity() { }
255 };
256
257
258 template<class Key, class Value>
259 class SmallHashDynamic
260 : public SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > {
261 friend class SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> >;
262
263 public:
264 typedef SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > Base;
265 static const double kThresholdGrow;
266 static const double kThresholdShrink;
267
268 111172 SmallHashDynamic() : Base() {
269 111172 num_migrates_ = 0;
270
271 // Properly set by Init
272 111172 threshold_grow_ = 0;
273 111172 threshold_shrink_ = 0;
274 111172 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 364 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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 364 if (&other == this)
284 ✗ return *this;
285
286 364 CopyFrom(other);
287 364 return *this;
288 }
289
290 22010754 uint32_t capacity() const { return Base::capacity_; }
291 166746042 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 131924 void SetThresholds() {
296 131924 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 131924 * kThresholdGrow);
298 131924 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 131924 * kThresholdShrink);
300 131924 }
301
302 271867693 void Grow() {
303
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 271867693 if (size() > threshold_grow_)
304 14736 Migrate(capacity() * 2);
305 271482265 }
306
307 20975952 void Shrink() {
308
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 20975952 if (size() < threshold_shrink_) {
309 10444144 const uint32_t target_capacity = capacity() / 2;
310
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 10441966 if (target_capacity >= Base::initial_capacity_)
311 2748 Migrate(target_capacity);
312 }
313 20978576 }
314
315 508 void ResetCapacity() {
316 508 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 508 Base::capacity_ = Base::initial_capacity_;
318 508 Base::AllocMemory();
319 508 SetThresholds();
320 508 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 5872 uint32_t *ShuffleIndices(const uint32_t N) {
326 5872 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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 89592656 for (unsigned i = 0; i < N; ++i)
329 89586784 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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 85628704 for (unsigned i = 0; i < N - 1; ++i) {
332 85642856 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 85622832 const uint32_t tmp = shuffled[i];
334 85622832 shuffled[i] = shuffled[swap_idx];
335 85622832 shuffled[swap_idx] = tmp;
336 }
337 364 return shuffled;
338 }
339
340 20232 void Migrate(const uint32_t new_capacity) {
341 20232 Key *old_keys = Base::keys_;
342 20232 Value *old_values = Base::values_;
343 20232 const uint32_t old_capacity = capacity();
344 20232 const uint32_t old_size = size();
345
346 20240 Base::capacity_ = new_capacity;
347 20240 SetThresholds();
348 20240 Base::AllocMemory();
349 20240 Base::DoClear(false);
350
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 20240 if (new_capacity < old_capacity) {
351 5504 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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 77582920 for (uint32_t i = 0; i < old_capacity; ++i) {
353
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 77582056 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 19451352 Base::Insert(old_keys[shuffled_indices[i]],
355 19451352 old_values[shuffled_indices[i]]);
356 }
357 }
358 864 smunmap(shuffled_indices);
359 } else {
360
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 151393736 for (uint32_t i = 0; i < old_capacity; ++i) {
361
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 151387232 if (old_keys[i] != Base::empty_key_)
362 113779168 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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 12008 assert(size() == old_size);
366
367 20240 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 20240 num_migrates_++;
369 20240 }
370
371 364 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 364 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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 5512948 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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 5512584 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 4000000 this->Insert(other.keys_[shuffled_indices[i]],
376 4000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 364 smunmap(shuffled_indices);
380 364 }
381
382 uint32_t num_migrates_;
383 uint32_t threshold_grow_;
384 uint32_t threshold_shrink_;
385 static Prng g_prng;
386 };
387
388
389 /**
390 * Distributes the key-value pairs over $n$ dynamic hash maps with individual
391 * mutexes. Hence low mutex contention, and benefits from multiple processors.
392 */
393 template<class Key, class Value>
394 class MultiHash {
395 public:
396 40 MultiHash() {
397 40 num_hashmaps_ = 0;
398 40 hashmaps_ = NULL;
399 40 locks_ = NULL;
400 40 }
401
402 40 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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 40 assert(num_hashmaps > 0);
405 40 const uint8_t N = num_hashmaps;
406 40 num_hashmaps_ = N;
407
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 1720 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 40 locks_ = static_cast<pthread_mutex_t *>(
409 40 smalloc(N * sizeof(pthread_mutex_t)));
410
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 1720 for (uint8_t i = 0; i < N; ++i) {
411 1680 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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 1680 assert(retval == 0);
413 1680 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 40 }
416
417 40 ~MultiHash() {
418
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 1720 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 1680 pthread_mutex_destroy(&locks_[i]);
420 }
421 40 free(locks_);
422
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 1720 delete[] hashmaps_;
423 40 }
424
425 4000000 bool Lookup(const Key &key, Value *value) {
426 4000000 uint8_t target = SelectHashmap(key);
427 4000000 Lock(target);
428 4000000 const bool result = hashmaps_[target].Lookup(key, value);
429 4000000 Unlock(target);
430 4000000 return result;
431 }
432
433 14925428 void Insert(const Key &key, const Value &value) {
434 14925428 uint8_t target = SelectHashmap(key);
435 14500484 Lock(target);
436 15119452 hashmaps_[target].Insert(key, value);
437 14272924 Unlock(target);
438 15565000 }
439
440 7060364 void Erase(const Key &key) {
441 7060364 uint8_t target = SelectHashmap(key);
442 6751640 Lock(target);
443 7254628 hashmaps_[target].Erase(key);
444 6503188 Unlock(target);
445 7343496 }
446
447 4 void Clear() {
448
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 172 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 168 Lock(i);
450
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 172 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 168 hashmaps_[i].Clear();
452
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 172 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 168 Unlock(i);
454 4 }
455
456 40 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 32 void GetSizes(uint32_t *sizes) {
459
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 1376 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 1344 Lock(i);
461 1344 sizes[i] = hashmaps_[i].size();
462 1344 Unlock(i);
463 }
464 32 }
465
466 void GetCollisionStats(uint64_t *num_collisions, uint32_t *max_collisions) {
467 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
468 Lock(i);
469 hashmaps_[i].GetCollisionStats(&num_collisions[i], &max_collisions[i]);
470 Unlock(i);
471 }
472 }
473
474 private:
475 25806016 inline uint8_t SelectHashmap(const Key &key) {
476 25806016 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 25404936 double bucket = static_cast<double>(hash)
478 25404936 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 25404936 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 25446136 inline void Lock(const uint8_t target) {
484 25446136 int retval = pthread_mutex_lock(&locks_[target]);
485
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 27405312 assert(retval == 0);
486 27405312 }
487
488 24789848 inline void Unlock(const uint8_t target) {
489 24789848 int retval = pthread_mutex_unlock(&locks_[target]);
490
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 27508420 assert(retval == 0);
491 27508420 }
492
493 uint8_t num_hashmaps_;
494 SmallHashDynamic<Key, Value> *hashmaps_;
495 pthread_mutex_t *locks_;
496 };
497
498
499 // initialize the static fields
500 template<class Key, class Value>
501 Prng SmallHashDynamic<Key, Value>::g_prng;
502
503 template<class Key, class Value, class Derived>
504 const double SmallHashBase<Key, Value, Derived>::kLoadFactor = 0.75;
505
506 template<class Key, class Value>
507 const double SmallHashDynamic<Key, Value>::kThresholdGrow = 0.75;
508
509 template<class Key, class Value>
510 const double SmallHashDynamic<Key, Value>::kThresholdShrink = 0.25;
511
512 #endif // CVMFS_SMALLHASH_H_
513