1/*
2 * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#include "precompiled.hpp"
26#include "classfile/altHashing.hpp"
27#include "classfile/javaClasses.inline.hpp"
28#include "gc/shared/stringdedup/stringDedup.hpp"
29#include "gc/shared/stringdedup/stringDedupTable.hpp"
30#include "gc/shared/suspendibleThreadSet.hpp"
31#include "logging/log.hpp"
32#include "memory/padded.inline.hpp"
33#include "memory/universe.hpp"
34#include "oops/access.inline.hpp"
35#include "oops/arrayOop.inline.hpp"
36#include "oops/oop.inline.hpp"
37#include "oops/typeArrayOop.hpp"
38#include "runtime/mutexLocker.hpp"
39#include "runtime/safepointVerifiers.hpp"
40
41//
42// List of deduplication table entries. Links table
43// entries together using their _next fields.
44//
45class StringDedupEntryList : public CHeapObj<mtGC> {
46private:
47 StringDedupEntry* _list;
48 size_t _length;
49
50public:
51 StringDedupEntryList() :
52 _list(NULL),
53 _length(0) {
54 }
55
56 void add(StringDedupEntry* entry) {
57 entry->set_next(_list);
58 _list = entry;
59 _length++;
60 }
61
62 StringDedupEntry* remove() {
63 StringDedupEntry* entry = _list;
64 if (entry != NULL) {
65 _list = entry->next();
66 _length--;
67 }
68 return entry;
69 }
70
71 StringDedupEntry* remove_all() {
72 StringDedupEntry* list = _list;
73 _list = NULL;
74 return list;
75 }
76
77 size_t length() {
78 return _length;
79 }
80};
81
82//
83// Cache of deduplication table entries. This cache provides fast allocation and
84// reuse of table entries to lower the pressure on the underlying allocator.
85// But more importantly, it provides fast/deferred freeing of table entries. This
86// is important because freeing of table entries is done during stop-the-world
87// phases and it is not uncommon for large number of entries to be freed at once.
88// Tables entries that are freed during these phases are placed onto a freelist in
89// the cache. The deduplication thread, which executes in a concurrent phase, will
90// later reuse or free the underlying memory for these entries.
91//
92// The cache allows for single-threaded allocations and multi-threaded frees.
93// Allocations are synchronized by StringDedupTable_lock as part of a table
94// modification.
95//
96class StringDedupEntryCache : public CHeapObj<mtGC> {
97private:
98 // One cache/overflow list per GC worker to allow lock less freeing of
99 // entries while doing a parallel scan of the table. Using PaddedEnd to
100 // avoid false sharing.
101 size_t _nlists;
102 size_t _max_list_length;
103 PaddedEnd<StringDedupEntryList>* _cached;
104 PaddedEnd<StringDedupEntryList>* _overflowed;
105
106public:
107 StringDedupEntryCache(size_t max_size);
108 ~StringDedupEntryCache();
109
110 // Set max number of table entries to cache.
111 void set_max_size(size_t max_size);
112
113 // Get a table entry from the cache, or allocate a new entry if the cache is empty.
114 StringDedupEntry* alloc();
115
116 // Insert a table entry into the cache.
117 void free(StringDedupEntry* entry, uint worker_id);
118
119 // Returns current number of entries in the cache.
120 size_t size();
121
122 // Deletes overflowed entries.
123 void delete_overflowed();
124};
125
126StringDedupEntryCache::StringDedupEntryCache(size_t max_size) :
127 _nlists(ParallelGCThreads),
128 _max_list_length(0),
129 _cached(PaddedArray<StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)),
130 _overflowed(PaddedArray<StringDedupEntryList, mtGC>::create_unfreeable((uint)_nlists)) {
131 set_max_size(max_size);
132}
133
134StringDedupEntryCache::~StringDedupEntryCache() {
135 ShouldNotReachHere();
136}
137
138void StringDedupEntryCache::set_max_size(size_t size) {
139 _max_list_length = size / _nlists;
140}
141
142StringDedupEntry* StringDedupEntryCache::alloc() {
143 for (size_t i = 0; i < _nlists; i++) {
144 StringDedupEntry* entry = _cached[i].remove();
145 if (entry != NULL) {
146 return entry;
147 }
148 }
149 return new StringDedupEntry();
150}
151
152void StringDedupEntryCache::free(StringDedupEntry* entry, uint worker_id) {
153 assert(entry->obj() != NULL, "Double free");
154 assert(worker_id < _nlists, "Invalid worker id");
155
156 entry->set_obj(NULL);
157 entry->set_hash(0);
158
159 if (_cached[worker_id].length() < _max_list_length) {
160 // Cache is not full
161 _cached[worker_id].add(entry);
162 } else {
163 // Cache is full, add to overflow list for later deletion
164 _overflowed[worker_id].add(entry);
165 }
166}
167
168size_t StringDedupEntryCache::size() {
169 size_t size = 0;
170 for (size_t i = 0; i < _nlists; i++) {
171 size += _cached[i].length();
172 }
173 return size;
174}
175
176void StringDedupEntryCache::delete_overflowed() {
177 double start = os::elapsedTime();
178 uintx count = 0;
179
180 for (size_t i = 0; i < _nlists; i++) {
181 StringDedupEntry* entry;
182
183 {
184 // The overflow list can be modified during safepoints, therefore
185 // we temporarily join the suspendible thread set while removing
186 // all entries from the list.
187 SuspendibleThreadSetJoiner sts_join;
188 entry = _overflowed[i].remove_all();
189 }
190
191 // Delete all entries
192 while (entry != NULL) {
193 StringDedupEntry* next = entry->next();
194 delete entry;
195 entry = next;
196 count++;
197 }
198 }
199
200 double end = os::elapsedTime();
201 log_trace(gc, stringdedup)("Deleted " UINTX_FORMAT " entries, " STRDEDUP_TIME_FORMAT_MS,
202 count, STRDEDUP_TIME_PARAM_MS(end - start));
203}
204
205StringDedupTable* StringDedupTable::_table = NULL;
206StringDedupEntryCache* StringDedupTable::_entry_cache = NULL;
207
208const size_t StringDedupTable::_min_size = (1 << 10); // 1024
209const size_t StringDedupTable::_max_size = (1 << 24); // 16777216
210const double StringDedupTable::_grow_load_factor = 2.0; // Grow table at 200% load
211const double StringDedupTable::_shrink_load_factor = _grow_load_factor / 3.0; // Shrink table at 67% load
212const double StringDedupTable::_max_cache_factor = 0.1; // Cache a maximum of 10% of the table size
213const uintx StringDedupTable::_rehash_multiple = 60; // Hash bucket has 60 times more collisions than expected
214const uintx StringDedupTable::_rehash_threshold = (uintx)(_rehash_multiple * _grow_load_factor);
215
216uintx StringDedupTable::_entries_added = 0;
217uintx StringDedupTable::_entries_removed = 0;
218uintx StringDedupTable::_resize_count = 0;
219uintx StringDedupTable::_rehash_count = 0;
220
221StringDedupTable* StringDedupTable::_resized_table = NULL;
222StringDedupTable* StringDedupTable::_rehashed_table = NULL;
223volatile size_t StringDedupTable::_claimed_index = 0;
224
225StringDedupTable::StringDedupTable(size_t size, jint hash_seed) :
226 _size(size),
227 _entries(0),
228 _shrink_threshold((uintx)(size * _shrink_load_factor)),
229 _grow_threshold((uintx)(size * _grow_load_factor)),
230 _rehash_needed(false),
231 _hash_seed(hash_seed) {
232 assert(is_power_of_2(size), "Table size must be a power of 2");
233 _buckets = NEW_C_HEAP_ARRAY(StringDedupEntry*, _size, mtGC);
234 memset(_buckets, 0, _size * sizeof(StringDedupEntry*));
235}
236
237StringDedupTable::~StringDedupTable() {
238 FREE_C_HEAP_ARRAY(G1StringDedupEntry*, _buckets);
239}
240
241void StringDedupTable::create() {
242 assert(_table == NULL, "One string deduplication table allowed");
243 _entry_cache = new StringDedupEntryCache(_min_size * _max_cache_factor);
244 _table = new StringDedupTable(_min_size);
245}
246
247void StringDedupTable::add(typeArrayOop value, bool latin1, unsigned int hash, StringDedupEntry** list) {
248 StringDedupEntry* entry = _entry_cache->alloc();
249 entry->set_obj(value);
250 entry->set_hash(hash);
251 entry->set_latin1(latin1);
252 entry->set_next(*list);
253 *list = entry;
254 _entries++;
255}
256
257void StringDedupTable::remove(StringDedupEntry** pentry, uint worker_id) {
258 StringDedupEntry* entry = *pentry;
259 *pentry = entry->next();
260 _entry_cache->free(entry, worker_id);
261}
262
263void StringDedupTable::transfer(StringDedupEntry** pentry, StringDedupTable* dest) {
264 StringDedupEntry* entry = *pentry;
265 *pentry = entry->next();
266 unsigned int hash = entry->hash();
267 size_t index = dest->hash_to_index(hash);
268 StringDedupEntry** list = dest->bucket(index);
269 entry->set_next(*list);
270 *list = entry;
271}
272
273typeArrayOop StringDedupTable::lookup(typeArrayOop value, bool latin1, unsigned int hash,
274 StringDedupEntry** list, uintx &count) {
275 for (StringDedupEntry* entry = *list; entry != NULL; entry = entry->next()) {
276 if (entry->hash() == hash && entry->latin1() == latin1) {
277 oop* obj_addr = (oop*)entry->obj_addr();
278 oop obj = NativeAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(obj_addr);
279 if (java_lang_String::value_equals(value, static_cast<typeArrayOop>(obj))) {
280 obj = NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(obj_addr);
281 return static_cast<typeArrayOop>(obj);
282 }
283 }
284 count++;
285 }
286
287 // Not found
288 return NULL;
289}
290
291typeArrayOop StringDedupTable::lookup_or_add_inner(typeArrayOop value, bool latin1, unsigned int hash) {
292 size_t index = hash_to_index(hash);
293 StringDedupEntry** list = bucket(index);
294 uintx count = 0;
295
296 // Lookup in list
297 typeArrayOop existing_value = lookup(value, latin1, hash, list, count);
298
299 // Check if rehash is needed
300 if (count > _rehash_threshold) {
301 _rehash_needed = true;
302 }
303
304 if (existing_value == NULL) {
305 // Not found, add new entry
306 add(value, latin1, hash, list);
307
308 // Update statistics
309 _entries_added++;
310 }
311
312 return existing_value;
313}
314
315unsigned int StringDedupTable::hash_code(typeArrayOop value, bool latin1) {
316 unsigned int hash;
317 int length = value->length();
318 if (latin1) {
319 const jbyte* data = (jbyte*)value->base(T_BYTE);
320 if (use_java_hash()) {
321 hash = java_lang_String::hash_code(data, length);
322 } else {
323 hash = AltHashing::murmur3_32(_table->_hash_seed, data, length);
324 }
325 } else {
326 length /= sizeof(jchar) / sizeof(jbyte); // Convert number of bytes to number of chars
327 const jchar* data = (jchar*)value->base(T_CHAR);
328 if (use_java_hash()) {
329 hash = java_lang_String::hash_code(data, length);
330 } else {
331 hash = AltHashing::murmur3_32(_table->_hash_seed, data, length);
332 }
333 }
334
335 return hash;
336}
337
338void StringDedupTable::deduplicate(oop java_string, StringDedupStat* stat) {
339 assert(java_lang_String::is_instance(java_string), "Must be a string");
340 NoSafepointVerifier nsv;
341
342 stat->inc_inspected();
343
344 typeArrayOop value = java_lang_String::value(java_string);
345 if (value == NULL) {
346 // String has no value
347 stat->inc_skipped();
348 return;
349 }
350
351 bool latin1 = java_lang_String::is_latin1(java_string);
352 unsigned int hash = 0;
353
354 if (use_java_hash()) {
355 if (!java_lang_String::hash_is_set(java_string)) {
356 stat->inc_hashed();
357 }
358 hash = java_lang_String::hash_code(java_string);
359 } else {
360 // Compute hash
361 hash = hash_code(value, latin1);
362 stat->inc_hashed();
363 }
364
365 typeArrayOop existing_value = lookup_or_add(value, latin1, hash);
366 if (oopDesc::equals_raw(existing_value, value)) {
367 // Same value, already known
368 stat->inc_known();
369 return;
370 }
371
372 // Get size of value array
373 uintx size_in_bytes = value->size() * HeapWordSize;
374 stat->inc_new(size_in_bytes);
375
376 if (existing_value != NULL) {
377 // Existing value found, deduplicate string
378 java_lang_String::set_value(java_string, existing_value);
379 stat->deduped(value, size_in_bytes);
380 }
381}
382
383bool StringDedupTable::is_resizing() {
384 return _resized_table != NULL;
385}
386
387bool StringDedupTable::is_rehashing() {
388 return _rehashed_table != NULL;
389}
390
391StringDedupTable* StringDedupTable::prepare_resize() {
392 size_t size = _table->_size;
393
394 // Check if the hashtable needs to be resized
395 if (_table->_entries > _table->_grow_threshold) {
396 // Grow table, double the size
397 size *= 2;
398 if (size > _max_size) {
399 // Too big, don't resize
400 return NULL;
401 }
402 } else if (_table->_entries < _table->_shrink_threshold) {
403 // Shrink table, half the size
404 size /= 2;
405 if (size < _min_size) {
406 // Too small, don't resize
407 return NULL;
408 }
409 } else if (StringDeduplicationResizeALot) {
410 // Force grow
411 size *= 2;
412 if (size > _max_size) {
413 // Too big, force shrink instead
414 size /= 4;
415 }
416 } else {
417 // Resize not needed
418 return NULL;
419 }
420
421 // Update statistics
422 _resize_count++;
423
424 // Update max cache size
425 _entry_cache->set_max_size(size * _max_cache_factor);
426
427 // Allocate the new table. The new table will be populated by workers
428 // calling unlink_or_oops_do() and finally installed by finish_resize().
429 return new StringDedupTable(size, _table->_hash_seed);
430}
431
432void StringDedupTable::finish_resize(StringDedupTable* resized_table) {
433 assert(resized_table != NULL, "Invalid table");
434
435 resized_table->_entries = _table->_entries;
436
437 // Free old table
438 delete _table;
439
440 // Install new table
441 _table = resized_table;
442}
443
444void StringDedupTable::unlink_or_oops_do(StringDedupUnlinkOrOopsDoClosure* cl, uint worker_id) {
445 // The table is divided into partitions to allow lock-less parallel processing by
446 // multiple worker threads. A worker thread first claims a partition, which ensures
447 // exclusive access to that part of the table, then continues to process it. To allow
448 // shrinking of the table in parallel we also need to make sure that the same worker
449 // thread processes all partitions where entries will hash to the same destination
450 // partition. Since the table size is always a power of two and we always shrink by
451 // dividing the table in half, we know that for a given partition there is only one
452 // other partition whoes entries will hash to the same destination partition. That
453 // other partition is always the sibling partition in the second half of the table.
454 // For example, if the table is divided into 8 partitions, the sibling of partition 0
455 // is partition 4, the sibling of partition 1 is partition 5, etc.
456 size_t table_half = _table->_size / 2;
457
458 // Let each partition be one page worth of buckets
459 size_t partition_size = MIN2(table_half, os::vm_page_size() / sizeof(StringDedupEntry*));
460 assert(table_half % partition_size == 0, "Invalid partition size");
461
462 // Number of entries removed during the scan
463 uintx removed = 0;
464
465 for (;;) {
466 // Grab next partition to scan
467 size_t partition_begin = claim_table_partition(partition_size);
468 size_t partition_end = partition_begin + partition_size;
469 if (partition_begin >= table_half) {
470 // End of table
471 break;
472 }
473
474 // Scan the partition followed by the sibling partition in the second half of the table
475 removed += unlink_or_oops_do(cl, partition_begin, partition_end, worker_id);
476 removed += unlink_or_oops_do(cl, table_half + partition_begin, table_half + partition_end, worker_id);
477 }
478
479 // Delayed update to avoid contention on the table lock
480 if (removed > 0) {
481 MutexLocker ml(StringDedupTable_lock, Mutex::_no_safepoint_check_flag);
482 _table->_entries -= removed;
483 _entries_removed += removed;
484 }
485}
486
487uintx StringDedupTable::unlink_or_oops_do(StringDedupUnlinkOrOopsDoClosure* cl,
488 size_t partition_begin,
489 size_t partition_end,
490 uint worker_id) {
491 uintx removed = 0;
492 for (size_t bucket = partition_begin; bucket < partition_end; bucket++) {
493 StringDedupEntry** entry = _table->bucket(bucket);
494 while (*entry != NULL) {
495 oop* p = (oop*)(*entry)->obj_addr();
496 if (cl->is_alive(*p)) {
497 cl->keep_alive(p);
498 if (is_resizing()) {
499 // We are resizing the table, transfer entry to the new table
500 _table->transfer(entry, _resized_table);
501 } else {
502 if (is_rehashing()) {
503 // We are rehashing the table, rehash the entry but keep it
504 // in the table. We can't transfer entries into the new table
505 // at this point since we don't have exclusive access to all
506 // destination partitions. finish_rehash() will do a single
507 // threaded transfer of all entries.
508 typeArrayOop value = (typeArrayOop)*p;
509 bool latin1 = (*entry)->latin1();
510 unsigned int hash = hash_code(value, latin1);
511 (*entry)->set_hash(hash);
512 }
513
514 // Move to next entry
515 entry = (*entry)->next_addr();
516 }
517 } else {
518 // Not alive, remove entry from table
519 _table->remove(entry, worker_id);
520 removed++;
521 }
522 }
523 }
524
525 return removed;
526}
527
528void StringDedupTable::gc_prologue(bool resize_and_rehash_table) {
529 assert(!is_resizing() && !is_rehashing(), "Already in progress?");
530
531 _claimed_index = 0;
532 if (resize_and_rehash_table) {
533 // If both resize and rehash is needed, only do resize. Rehash of
534 // the table will eventually happen if the situation persists.
535 _resized_table = StringDedupTable::prepare_resize();
536 if (!is_resizing()) {
537 _rehashed_table = StringDedupTable::prepare_rehash();
538 }
539 }
540}
541
542void StringDedupTable::gc_epilogue() {
543 assert(!is_resizing() || !is_rehashing(), "Can not both resize and rehash");
544 assert(_claimed_index >= _table->_size / 2 || _claimed_index == 0, "All or nothing");
545
546 if (is_resizing()) {
547 StringDedupTable::finish_resize(_resized_table);
548 _resized_table = NULL;
549 } else if (is_rehashing()) {
550 StringDedupTable::finish_rehash(_rehashed_table);
551 _rehashed_table = NULL;
552 }
553}
554
555StringDedupTable* StringDedupTable::prepare_rehash() {
556 if (!_table->_rehash_needed && !StringDeduplicationRehashALot) {
557 // Rehash not needed
558 return NULL;
559 }
560
561 // Update statistics
562 _rehash_count++;
563
564 // Compute new hash seed
565 _table->_hash_seed = AltHashing::compute_seed();
566
567 // Allocate the new table, same size and hash seed
568 return new StringDedupTable(_table->_size, _table->_hash_seed);
569}
570
571void StringDedupTable::finish_rehash(StringDedupTable* rehashed_table) {
572 assert(rehashed_table != NULL, "Invalid table");
573
574 // Move all newly rehashed entries into the correct buckets in the new table
575 for (size_t bucket = 0; bucket < _table->_size; bucket++) {
576 StringDedupEntry** entry = _table->bucket(bucket);
577 while (*entry != NULL) {
578 _table->transfer(entry, rehashed_table);
579 }
580 }
581
582 rehashed_table->_entries = _table->_entries;
583
584 // Free old table
585 delete _table;
586
587 // Install new table
588 _table = rehashed_table;
589}
590
591size_t StringDedupTable::claim_table_partition(size_t partition_size) {
592 return Atomic::add(partition_size, &_claimed_index) - partition_size;
593}
594
595void StringDedupTable::verify() {
596 for (size_t bucket = 0; bucket < _table->_size; bucket++) {
597 // Verify entries
598 StringDedupEntry** entry = _table->bucket(bucket);
599 while (*entry != NULL) {
600 typeArrayOop value = (*entry)->obj();
601 guarantee(value != NULL, "Object must not be NULL");
602 guarantee(Universe::heap()->is_in_reserved(value), "Object must be on the heap");
603 guarantee(!value->is_forwarded(), "Object must not be forwarded");
604 guarantee(value->is_typeArray(), "Object must be a typeArrayOop");
605 bool latin1 = (*entry)->latin1();
606 unsigned int hash = hash_code(value, latin1);
607 guarantee((*entry)->hash() == hash, "Table entry has inorrect hash");
608 guarantee(_table->hash_to_index(hash) == bucket, "Table entry has incorrect index");
609 entry = (*entry)->next_addr();
610 }
611
612 // Verify that we do not have entries with identical oops or identical arrays.
613 // We only need to compare entries in the same bucket. If the same oop or an
614 // identical array has been inserted more than once into different/incorrect
615 // buckets the verification step above will catch that.
616 StringDedupEntry** entry1 = _table->bucket(bucket);
617 while (*entry1 != NULL) {
618 typeArrayOop value1 = (*entry1)->obj();
619 bool latin1_1 = (*entry1)->latin1();
620 StringDedupEntry** entry2 = (*entry1)->next_addr();
621 while (*entry2 != NULL) {
622 typeArrayOop value2 = (*entry2)->obj();
623 bool latin1_2 = (*entry2)->latin1();
624 guarantee(latin1_1 != latin1_2 || !java_lang_String::value_equals(value1, value2), "Table entries must not have identical arrays");
625 entry2 = (*entry2)->next_addr();
626 }
627 entry1 = (*entry1)->next_addr();
628 }
629 }
630}
631
632void StringDedupTable::clean_entry_cache() {
633 _entry_cache->delete_overflowed();
634}
635
636void StringDedupTable::print_statistics() {
637 Log(gc, stringdedup) log;
638 log.debug(" Table");
639 log.debug(" Memory Usage: " STRDEDUP_BYTES_FORMAT_NS,
640 STRDEDUP_BYTES_PARAM(_table->_size * sizeof(StringDedupEntry*) + (_table->_entries + _entry_cache->size()) * sizeof(StringDedupEntry)));
641 log.debug(" Size: " SIZE_FORMAT ", Min: " SIZE_FORMAT ", Max: " SIZE_FORMAT, _table->_size, _min_size, _max_size);
642 log.debug(" Entries: " UINTX_FORMAT ", Load: " STRDEDUP_PERCENT_FORMAT_NS ", Cached: " UINTX_FORMAT ", Added: " UINTX_FORMAT ", Removed: " UINTX_FORMAT,
643 _table->_entries, percent_of((size_t)_table->_entries, _table->_size), _entry_cache->size(), _entries_added, _entries_removed);
644 log.debug(" Resize Count: " UINTX_FORMAT ", Shrink Threshold: " UINTX_FORMAT "(" STRDEDUP_PERCENT_FORMAT_NS "), Grow Threshold: " UINTX_FORMAT "(" STRDEDUP_PERCENT_FORMAT_NS ")",
645 _resize_count, _table->_shrink_threshold, _shrink_load_factor * 100.0, _table->_grow_threshold, _grow_load_factor * 100.0);
646 log.debug(" Rehash Count: " UINTX_FORMAT ", Rehash Threshold: " UINTX_FORMAT ", Hash Seed: 0x%x", _rehash_count, _rehash_threshold, _table->_hash_seed);
647 log.debug(" Age Threshold: " UINTX_FORMAT, StringDeduplicationAgeThreshold);
648}
649