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dynahash.c
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1 /*-------------------------------------------------------------------------
2  *
3  * dynahash.c
4  * dynamic hash tables
5  *
6  * dynahash.c supports both local-to-a-backend hash tables and hash tables in
7  * shared memory. For shared hash tables, it is the caller's responsibility
8  * to provide appropriate access interlocking. The simplest convention is
9  * that a single LWLock protects the whole hash table. Searches (HASH_FIND or
10  * hash_seq_search) need only shared lock, but any update requires exclusive
11  * lock. For heavily-used shared tables, the single-lock approach creates a
12  * concurrency bottleneck, so we also support "partitioned" locking wherein
13  * there are multiple LWLocks guarding distinct subsets of the table. To use
14  * a hash table in partitioned mode, the HASH_PARTITION flag must be given
15  * to hash_create. This prevents any attempt to split buckets on-the-fly.
16  * Therefore, each hash bucket chain operates independently, and no fields
17  * of the hash header change after init except nentries and freeList.
18  * (A partitioned table uses multiple copies of those fields, guarded by
19  * spinlocks, for additional concurrency.)
20  * This lets any subset of the hash buckets be treated as a separately
21  * lockable partition. We expect callers to use the low-order bits of a
22  * lookup key's hash value as a partition number --- this will work because
23  * of the way calc_bucket() maps hash values to bucket numbers.
24  *
25  * For hash tables in shared memory, the memory allocator function should
26  * match malloc's semantics of returning NULL on failure. For hash tables
27  * in local memory, we typically use palloc() which will throw error on
28  * failure. The code in this file has to cope with both cases.
29  *
30  * dynahash.c provides support for these types of lookup keys:
31  *
32  * 1. Null-terminated C strings (truncated if necessary to fit in keysize),
33  * compared as though by strcmp(). This is the default behavior.
34  *
35  * 2. Arbitrary binary data of size keysize, compared as though by memcmp().
36  * (Caller must ensure there are no undefined padding bits in the keys!)
37  * This is selected by specifying HASH_BLOBS flag to hash_create.
38  *
39  * 3. More complex key behavior can be selected by specifying user-supplied
40  * hashing, comparison, and/or key-copying functions. At least a hashing
41  * function must be supplied; comparison defaults to memcmp() and key copying
42  * to memcpy() when a user-defined hashing function is selected.
43  *
44  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
45  * Portions Copyright (c) 1994, Regents of the University of California
46  *
47  *
48  * IDENTIFICATION
49  * src/backend/utils/hash/dynahash.c
50  *
51  *-------------------------------------------------------------------------
52  */
53 
54 /*
55  * Original comments:
56  *
57  * Dynamic hashing, after CACM April 1988 pp 446-457, by Per-Ake Larson.
58  * Coded into C, with minor code improvements, and with hsearch(3) interface,
59  * by ejp@ausmelb.oz, Jul 26, 1988: 13:16;
60  * also, hcreate/hdestroy routines added to simulate hsearch(3).
61  *
62  * These routines simulate hsearch(3) and family, with the important
63  * difference that the hash table is dynamic - can grow indefinitely
64  * beyond its original size (as supplied to hcreate()).
65  *
66  * Performance appears to be comparable to that of hsearch(3).
67  * The 'source-code' options referred to in hsearch(3)'s 'man' page
68  * are not implemented; otherwise functionality is identical.
69  *
70  * Compilation controls:
71  * HASH_DEBUG controls some informative traces, mainly for debugging.
72  * HASH_STATISTICS causes HashAccesses and HashCollisions to be maintained;
73  * when combined with HASH_DEBUG, these are displayed by hdestroy().
74  *
75  * Problems & fixes to ejp@ausmelb.oz. WARNING: relies on pre-processor
76  * concatenation property, in probably unnecessary code 'optimization'.
77  *
78  * Modified margo@postgres.berkeley.edu February 1990
79  * added multiple table interface
80  * Modified by sullivan@postgres.berkeley.edu April 1990
81  * changed ctl structure for shared memory
82  */
83 
84 #include "postgres.h"
85 
86 #include <limits.h>
87 
88 #include "access/xact.h"
89 #include "storage/shmem.h"
90 #include "storage/spin.h"
91 #include "utils/dynahash.h"
92 #include "utils/memutils.h"
93 
94 
95 /*
96  * Constants
97  *
98  * A hash table has a top-level "directory", each of whose entries points
99  * to a "segment" of ssize bucket headers. The maximum number of hash
100  * buckets is thus dsize * ssize (but dsize may be expansible). Of course,
101  * the number of records in the table can be larger, but we don't want a
102  * whole lot of records per bucket or performance goes down.
103  *
104  * In a hash table allocated in shared memory, the directory cannot be
105  * expanded because it must stay at a fixed address. The directory size
106  * should be selected using hash_select_dirsize (and you'd better have
107  * a good idea of the maximum number of entries!). For non-shared hash
108  * tables, the initial directory size can be left at the default.
109  */
110 #define DEF_SEGSIZE 256
111 #define DEF_SEGSIZE_SHIFT 8 /* must be log2(DEF_SEGSIZE) */
112 #define DEF_DIRSIZE 256
113 #define DEF_FFACTOR 1 /* default fill factor */
114 
115 /* Number of freelists to be used for a partitioned hash table. */
116 #define NUM_FREELISTS 32
117 
118 /* A hash bucket is a linked list of HASHELEMENTs */
120 
121 /* A hash segment is an array of bucket headers */
123 
124 /*
125  * Per-freelist data.
126  *
127  * In a partitioned hash table, each freelist is associated with a specific
128  * set of hashcodes, as determined by the FREELIST_IDX() macro below.
129  * nentries tracks the number of live hashtable entries having those hashcodes
130  * (NOT the number of entries in the freelist, as you might expect).
131  *
132  * The coverage of a freelist might be more or less than one partition, so it
133  * needs its own lock rather than relying on caller locking. Relying on that
134  * wouldn't work even if the coverage was the same, because of the occasional
135  * need to "borrow" entries from another freelist; see get_hash_entry().
136  *
137  * Using an array of FreeListData instead of separate arrays of mutexes,
138  * nentries and freeLists helps to reduce sharing of cache lines between
139  * different mutexes.
140  */
141 typedef struct
142 {
143  slock_t mutex; /* spinlock for this freelist */
144  long nentries; /* number of entries in associated buckets */
145  HASHELEMENT *freeList; /* chain of free elements */
146 } FreeListData;
147 
148 /*
149  * Header structure for a hash table --- contains all changeable info
150  *
151  * In a shared-memory hash table, the HASHHDR is in shared memory, while
152  * each backend has a local HTAB struct. For a non-shared table, there isn't
153  * any functional difference between HASHHDR and HTAB, but we separate them
154  * anyway to share code between shared and non-shared tables.
155  */
156 struct HASHHDR
157 {
158  /*
159  * The freelist can become a point of contention in high-concurrency hash
160  * tables, so we use an array of freelists, each with its own mutex and
161  * nentries count, instead of just a single one. Although the freelists
162  * normally operate independently, we will scavenge entries from freelists
163  * other than a hashcode's default freelist when necessary.
164  *
165  * If the hash table is not partitioned, only freeList[0] is used and its
166  * spinlock is not used at all; callers' locking is assumed sufficient.
167  */
169 
170  /* These fields can change, but not in a partitioned table */
171  /* Also, dsize can't change in a shared table, even if unpartitioned */
172  long dsize; /* directory size */
173  long nsegs; /* number of allocated segments (<= dsize) */
174  uint32 max_bucket; /* ID of maximum bucket in use */
175  uint32 high_mask; /* mask to modulo into entire table */
176  uint32 low_mask; /* mask to modulo into lower half of table */
177 
178  /* These fields are fixed at hashtable creation */
179  Size keysize; /* hash key length in bytes */
180  Size entrysize; /* total user element size in bytes */
181  long num_partitions; /* # partitions (must be power of 2), or 0 */
182  long ffactor; /* target fill factor */
183  long max_dsize; /* 'dsize' limit if directory is fixed size */
184  long ssize; /* segment size --- must be power of 2 */
185  int sshift; /* segment shift = log2(ssize) */
186  int nelem_alloc; /* number of entries to allocate at once */
187 
188 #ifdef HASH_STATISTICS
189 
190  /*
191  * Count statistics here. NB: stats code doesn't bother with mutex, so
192  * counts could be corrupted a bit in a partitioned table.
193  */
194  long accesses;
195  long collisions;
196 #endif
197 };
198 
199 #define IS_PARTITIONED(hctl) ((hctl)->num_partitions != 0)
200 
201 #define FREELIST_IDX(hctl, hashcode) \
202  (IS_PARTITIONED(hctl) ? (hashcode) % NUM_FREELISTS : 0)
203 
204 /*
205  * Top control structure for a hashtable --- in a shared table, each backend
206  * has its own copy (OK since no fields change at runtime)
207  */
208 struct HTAB
209 {
210  HASHHDR *hctl; /* => shared control information */
211  HASHSEGMENT *dir; /* directory of segment starts */
212  HashValueFunc hash; /* hash function */
213  HashCompareFunc match; /* key comparison function */
214  HashCopyFunc keycopy; /* key copying function */
215  HashAllocFunc alloc; /* memory allocator */
216  MemoryContext hcxt; /* memory context if default allocator used */
217  char *tabname; /* table name (for error messages) */
218  bool isshared; /* true if table is in shared memory */
219  bool isfixed; /* if true, don't enlarge */
220 
221  /* freezing a shared table isn't allowed, so we can keep state here */
222  bool frozen; /* true = no more inserts allowed */
223 
224  /* We keep local copies of these fixed values to reduce contention */
225  Size keysize; /* hash key length in bytes */
226  long ssize; /* segment size --- must be power of 2 */
227  int sshift; /* segment shift = log2(ssize) */
228 };
229 
230 /*
231  * Key (also entry) part of a HASHELEMENT
232  */
233 #define ELEMENTKEY(helem) (((char *)(helem)) + MAXALIGN(sizeof(HASHELEMENT)))
234 
235 /*
236  * Obtain element pointer given pointer to key
237  */
238 #define ELEMENT_FROM_KEY(key) \
239  ((HASHELEMENT *) (((char *) (key)) - MAXALIGN(sizeof(HASHELEMENT))))
240 
241 /*
242  * Fast MOD arithmetic, assuming that y is a power of 2 !
243  */
244 #define MOD(x,y) ((x) & ((y)-1))
245 
246 #if HASH_STATISTICS
247 static long hash_accesses,
248  hash_collisions,
249  hash_expansions;
250 #endif
251 
252 /*
253  * Private function prototypes
254  */
255 static void *DynaHashAlloc(Size size);
256 static HASHSEGMENT seg_alloc(HTAB *hashp);
257 static bool element_alloc(HTAB *hashp, int nelem, int freelist_idx);
258 static bool dir_realloc(HTAB *hashp);
259 static bool expand_table(HTAB *hashp);
260 static HASHBUCKET get_hash_entry(HTAB *hashp, int freelist_idx);
261 static void hdefault(HTAB *hashp);
262 static int choose_nelem_alloc(Size entrysize);
263 static bool init_htab(HTAB *hashp, long nelem);
264 static void hash_corrupted(HTAB *hashp);
265 static long next_pow2_long(long num);
266 static int next_pow2_int(long num);
267 static void register_seq_scan(HTAB *hashp);
268 static void deregister_seq_scan(HTAB *hashp);
269 static bool has_seq_scans(HTAB *hashp);
270 
271 
272 /*
273  * memory allocation support
274  */
276 
277 static void *
279 {
280  Assert(MemoryContextIsValid(CurrentDynaHashCxt));
281  return MemoryContextAlloc(CurrentDynaHashCxt, size);
282 }
283 
284 
285 /*
286  * HashCompareFunc for string keys
287  *
288  * Because we copy keys with strlcpy(), they will be truncated at keysize-1
289  * bytes, so we can only compare that many ... hence strncmp is almost but
290  * not quite the right thing.
291  */
292 static int
293 string_compare(const char *key1, const char *key2, Size keysize)
294 {
295  return strncmp(key1, key2, keysize - 1);
296 }
297 
298 
299 /************************** CREATE ROUTINES **********************/
300 
301 /*
302  * hash_create -- create a new dynamic hash table
303  *
304  * tabname: a name for the table (for debugging purposes)
305  * nelem: maximum number of elements expected
306  * *info: additional table parameters, as indicated by flags
307  * flags: bitmask indicating which parameters to take from *info
308  *
309  * Note: for a shared-memory hashtable, nelem needs to be a pretty good
310  * estimate, since we can't expand the table on the fly. But an unshared
311  * hashtable can be expanded on-the-fly, so it's better for nelem to be
312  * on the small side and let the table grow if it's exceeded. An overly
313  * large nelem will penalize hash_seq_search speed without buying much.
314  */
315 HTAB *
316 hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
317 {
318  HTAB *hashp;
319  HASHHDR *hctl;
320 
321  /*
322  * For shared hash tables, we have a local hash header (HTAB struct) that
323  * we allocate in TopMemoryContext; all else is in shared memory.
324  *
325  * For non-shared hash tables, everything including the hash header is in
326  * a memory context created specially for the hash table --- this makes
327  * hash_destroy very simple. The memory context is made a child of either
328  * a context specified by the caller, or TopMemoryContext if nothing is
329  * specified.
330  */
331  if (flags & HASH_SHARED_MEM)
332  {
333  /* Set up to allocate the hash header */
334  CurrentDynaHashCxt = TopMemoryContext;
335  }
336  else
337  {
338  /* Create the hash table's private memory context */
339  if (flags & HASH_CONTEXT)
340  CurrentDynaHashCxt = info->hcxt;
341  else
342  CurrentDynaHashCxt = TopMemoryContext;
343  CurrentDynaHashCxt = AllocSetContextCreate(CurrentDynaHashCxt,
344  "dynahash",
346  }
347 
348  /* Initialize the hash header, plus a copy of the table name */
349  hashp = (HTAB *) DynaHashAlloc(sizeof(HTAB) + strlen(tabname) + 1);
350  MemSet(hashp, 0, sizeof(HTAB));
351 
352  hashp->tabname = (char *) (hashp + 1);
353  strcpy(hashp->tabname, tabname);
354 
355  /* If we have a private context, label it with hashtable's name */
356  if (!(flags & HASH_SHARED_MEM))
357  MemoryContextSetIdentifier(CurrentDynaHashCxt, hashp->tabname);
358 
359  /*
360  * Select the appropriate hash function (see comments at head of file).
361  */
362  if (flags & HASH_FUNCTION)
363  hashp->hash = info->hash;
364  else if (flags & HASH_BLOBS)
365  {
366  /* We can optimize hashing for common key sizes */
367  Assert(flags & HASH_ELEM);
368  if (info->keysize == sizeof(uint32))
369  hashp->hash = uint32_hash;
370  else
371  hashp->hash = tag_hash;
372  }
373  else
374  hashp->hash = string_hash; /* default hash function */
375 
376  /*
377  * If you don't specify a match function, it defaults to string_compare if
378  * you used string_hash (either explicitly or by default) and to memcmp
379  * otherwise.
380  *
381  * Note: explicitly specifying string_hash is deprecated, because this
382  * might not work for callers in loadable modules on some platforms due to
383  * referencing a trampoline instead of the string_hash function proper.
384  * Just let it default, eh?
385  */
386  if (flags & HASH_COMPARE)
387  hashp->match = info->match;
388  else if (hashp->hash == string_hash)
390  else
391  hashp->match = memcmp;
392 
393  /*
394  * Similarly, the key-copying function defaults to strlcpy or memcpy.
395  */
396  if (flags & HASH_KEYCOPY)
397  hashp->keycopy = info->keycopy;
398  else if (hashp->hash == string_hash)
399  hashp->keycopy = (HashCopyFunc) strlcpy;
400  else
401  hashp->keycopy = memcpy;
402 
403  /* And select the entry allocation function, too. */
404  if (flags & HASH_ALLOC)
405  hashp->alloc = info->alloc;
406  else
407  hashp->alloc = DynaHashAlloc;
408 
409  if (flags & HASH_SHARED_MEM)
410  {
411  /*
412  * ctl structure and directory are preallocated for shared memory
413  * tables. Note that HASH_DIRSIZE and HASH_ALLOC had better be set as
414  * well.
415  */
416  hashp->hctl = info->hctl;
417  hashp->dir = (HASHSEGMENT *) (((char *) info->hctl) + sizeof(HASHHDR));
418  hashp->hcxt = NULL;
419  hashp->isshared = true;
420 
421  /* hash table already exists, we're just attaching to it */
422  if (flags & HASH_ATTACH)
423  {
424  /* make local copies of some heavily-used values */
425  hctl = hashp->hctl;
426  hashp->keysize = hctl->keysize;
427  hashp->ssize = hctl->ssize;
428  hashp->sshift = hctl->sshift;
429 
430  return hashp;
431  }
432  }
433  else
434  {
435  /* setup hash table defaults */
436  hashp->hctl = NULL;
437  hashp->dir = NULL;
438  hashp->hcxt = CurrentDynaHashCxt;
439  hashp->isshared = false;
440  }
441 
442  if (!hashp->hctl)
443  {
444  hashp->hctl = (HASHHDR *) hashp->alloc(sizeof(HASHHDR));
445  if (!hashp->hctl)
446  ereport(ERROR,
447  (errcode(ERRCODE_OUT_OF_MEMORY),
448  errmsg("out of memory")));
449  }
450 
451  hashp->frozen = false;
452 
453  hdefault(hashp);
454 
455  hctl = hashp->hctl;
456 
457  if (flags & HASH_PARTITION)
458  {
459  /* Doesn't make sense to partition a local hash table */
460  Assert(flags & HASH_SHARED_MEM);
461 
462  /*
463  * The number of partitions had better be a power of 2. Also, it must
464  * be less than INT_MAX (see init_htab()), so call the int version of
465  * next_pow2.
466  */
468 
469  hctl->num_partitions = info->num_partitions;
470  }
471 
472  if (flags & HASH_SEGMENT)
473  {
474  hctl->ssize = info->ssize;
475  hctl->sshift = my_log2(info->ssize);
476  /* ssize had better be a power of 2 */
477  Assert(hctl->ssize == (1L << hctl->sshift));
478  }
479  if (flags & HASH_FFACTOR)
480  hctl->ffactor = info->ffactor;
481 
482  /*
483  * SHM hash tables have fixed directory size passed by the caller.
484  */
485  if (flags & HASH_DIRSIZE)
486  {
487  hctl->max_dsize = info->max_dsize;
488  hctl->dsize = info->dsize;
489  }
490 
491  /*
492  * hash table now allocates space for key and data but you have to say how
493  * much space to allocate
494  */
495  if (flags & HASH_ELEM)
496  {
497  Assert(info->entrysize >= info->keysize);
498  hctl->keysize = info->keysize;
499  hctl->entrysize = info->entrysize;
500  }
501 
502  /* make local copies of heavily-used constant fields */
503  hashp->keysize = hctl->keysize;
504  hashp->ssize = hctl->ssize;
505  hashp->sshift = hctl->sshift;
506 
507  /* Build the hash directory structure */
508  if (!init_htab(hashp, nelem))
509  elog(ERROR, "failed to initialize hash table \"%s\"", hashp->tabname);
510 
511  /*
512  * For a shared hash table, preallocate the requested number of elements.
513  * This reduces problems with run-time out-of-shared-memory conditions.
514  *
515  * For a non-shared hash table, preallocate the requested number of
516  * elements if it's less than our chosen nelem_alloc. This avoids wasting
517  * space if the caller correctly estimates a small table size.
518  */
519  if ((flags & HASH_SHARED_MEM) ||
520  nelem < hctl->nelem_alloc)
521  {
522  int i,
523  freelist_partitions,
524  nelem_alloc,
525  nelem_alloc_first;
526 
527  /*
528  * If hash table is partitioned, give each freelist an equal share of
529  * the initial allocation. Otherwise only freeList[0] is used.
530  */
531  if (IS_PARTITIONED(hashp->hctl))
532  freelist_partitions = NUM_FREELISTS;
533  else
534  freelist_partitions = 1;
535 
536  nelem_alloc = nelem / freelist_partitions;
537  if (nelem_alloc <= 0)
538  nelem_alloc = 1;
539 
540  /*
541  * Make sure we'll allocate all the requested elements; freeList[0]
542  * gets the excess if the request isn't divisible by NUM_FREELISTS.
543  */
544  if (nelem_alloc * freelist_partitions < nelem)
545  nelem_alloc_first =
546  nelem - nelem_alloc * (freelist_partitions - 1);
547  else
548  nelem_alloc_first = nelem_alloc;
549 
550  for (i = 0; i < freelist_partitions; i++)
551  {
552  int temp = (i == 0) ? nelem_alloc_first : nelem_alloc;
553 
554  if (!element_alloc(hashp, temp, i))
555  ereport(ERROR,
556  (errcode(ERRCODE_OUT_OF_MEMORY),
557  errmsg("out of memory")));
558  }
559  }
560 
561  if (flags & HASH_FIXED_SIZE)
562  hashp->isfixed = true;
563  return hashp;
564 }
565 
566 /*
567  * Set default HASHHDR parameters.
568  */
569 static void
570 hdefault(HTAB *hashp)
571 {
572  HASHHDR *hctl = hashp->hctl;
573 
574  MemSet(hctl, 0, sizeof(HASHHDR));
575 
576  hctl->dsize = DEF_DIRSIZE;
577  hctl->nsegs = 0;
578 
579  /* rather pointless defaults for key & entry size */
580  hctl->keysize = sizeof(char *);
581  hctl->entrysize = 2 * sizeof(char *);
582 
583  hctl->num_partitions = 0; /* not partitioned */
584 
585  hctl->ffactor = DEF_FFACTOR;
586 
587  /* table has no fixed maximum size */
588  hctl->max_dsize = NO_MAX_DSIZE;
589 
590  hctl->ssize = DEF_SEGSIZE;
591  hctl->sshift = DEF_SEGSIZE_SHIFT;
592 
593 #ifdef HASH_STATISTICS
594  hctl->accesses = hctl->collisions = 0;
595 #endif
596 }
597 
598 /*
599  * Given the user-specified entry size, choose nelem_alloc, ie, how many
600  * elements to add to the hash table when we need more.
601  */
602 static int
604 {
605  int nelem_alloc;
606  Size elementSize;
607  Size allocSize;
608 
609  /* Each element has a HASHELEMENT header plus user data. */
610  /* NB: this had better match element_alloc() */
611  elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
612 
613  /*
614  * The idea here is to choose nelem_alloc at least 32, but round up so
615  * that the allocation request will be a power of 2 or just less. This
616  * makes little difference for hash tables in shared memory, but for hash
617  * tables managed by palloc, the allocation request will be rounded up to
618  * a power of 2 anyway. If we fail to take this into account, we'll waste
619  * as much as half the allocated space.
620  */
621  allocSize = 32 * 4; /* assume elementSize at least 8 */
622  do
623  {
624  allocSize <<= 1;
625  nelem_alloc = allocSize / elementSize;
626  } while (nelem_alloc < 32);
627 
628  return nelem_alloc;
629 }
630 
631 /*
632  * Compute derived fields of hctl and build the initial directory/segment
633  * arrays
634  */
635 static bool
636 init_htab(HTAB *hashp, long nelem)
637 {
638  HASHHDR *hctl = hashp->hctl;
639  HASHSEGMENT *segp;
640  int nbuckets;
641  int nsegs;
642  int i;
643 
644  /*
645  * initialize mutexes if it's a partitioned table
646  */
647  if (IS_PARTITIONED(hctl))
648  for (i = 0; i < NUM_FREELISTS; i++)
649  SpinLockInit(&(hctl->freeList[i].mutex));
650 
651  /*
652  * Divide number of elements by the fill factor to determine a desired
653  * number of buckets. Allocate space for the next greater power of two
654  * number of buckets
655  */
656  nbuckets = next_pow2_int((nelem - 1) / hctl->ffactor + 1);
657 
658  /*
659  * In a partitioned table, nbuckets must be at least equal to
660  * num_partitions; were it less, keys with apparently different partition
661  * numbers would map to the same bucket, breaking partition independence.
662  * (Normally nbuckets will be much bigger; this is just a safety check.)
663  */
664  while (nbuckets < hctl->num_partitions)
665  nbuckets <<= 1;
666 
667  hctl->max_bucket = hctl->low_mask = nbuckets - 1;
668  hctl->high_mask = (nbuckets << 1) - 1;
669 
670  /*
671  * Figure number of directory segments needed, round up to a power of 2
672  */
673  nsegs = (nbuckets - 1) / hctl->ssize + 1;
674  nsegs = next_pow2_int(nsegs);
675 
676  /*
677  * Make sure directory is big enough. If pre-allocated directory is too
678  * small, choke (caller screwed up).
679  */
680  if (nsegs > hctl->dsize)
681  {
682  if (!(hashp->dir))
683  hctl->dsize = nsegs;
684  else
685  return false;
686  }
687 
688  /* Allocate a directory */
689  if (!(hashp->dir))
690  {
691  CurrentDynaHashCxt = hashp->hcxt;
692  hashp->dir = (HASHSEGMENT *)
693  hashp->alloc(hctl->dsize * sizeof(HASHSEGMENT));
694  if (!hashp->dir)
695  return false;
696  }
697 
698  /* Allocate initial segments */
699  for (segp = hashp->dir; hctl->nsegs < nsegs; hctl->nsegs++, segp++)
700  {
701  *segp = seg_alloc(hashp);
702  if (*segp == NULL)
703  return false;
704  }
705 
706  /* Choose number of entries to allocate at a time */
708 
709 #if HASH_DEBUG
710  fprintf(stderr, "init_htab:\n%s%p\n%s%ld\n%s%ld\n%s%d\n%s%ld\n%s%u\n%s%x\n%s%x\n%s%ld\n",
711  "TABLE POINTER ", hashp,
712  "DIRECTORY SIZE ", hctl->dsize,
713  "SEGMENT SIZE ", hctl->ssize,
714  "SEGMENT SHIFT ", hctl->sshift,
715  "FILL FACTOR ", hctl->ffactor,
716  "MAX BUCKET ", hctl->max_bucket,
717  "HIGH MASK ", hctl->high_mask,
718  "LOW MASK ", hctl->low_mask,
719  "NSEGS ", hctl->nsegs);
720 #endif
721  return true;
722 }
723 
724 /*
725  * Estimate the space needed for a hashtable containing the given number
726  * of entries of given size.
727  * NOTE: this is used to estimate the footprint of hashtables in shared
728  * memory; therefore it does not count HTAB which is in local memory.
729  * NB: assumes that all hash structure parameters have default values!
730  */
731 Size
733 {
734  Size size;
735  long nBuckets,
736  nSegments,
737  nDirEntries,
738  nElementAllocs,
739  elementSize,
740  elementAllocCnt;
741 
742  /* estimate number of buckets wanted */
743  nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
744  /* # of segments needed for nBuckets */
745  nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
746  /* directory entries */
747  nDirEntries = DEF_DIRSIZE;
748  while (nDirEntries < nSegments)
749  nDirEntries <<= 1; /* dir_alloc doubles dsize at each call */
750 
751  /* fixed control info */
752  size = MAXALIGN(sizeof(HASHHDR)); /* but not HTAB, per above */
753  /* directory */
754  size = add_size(size, mul_size(nDirEntries, sizeof(HASHSEGMENT)));
755  /* segments */
756  size = add_size(size, mul_size(nSegments,
757  MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET))));
758  /* elements --- allocated in groups of choose_nelem_alloc() entries */
759  elementAllocCnt = choose_nelem_alloc(entrysize);
760  nElementAllocs = (num_entries - 1) / elementAllocCnt + 1;
761  elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
762  size = add_size(size,
763  mul_size(nElementAllocs,
764  mul_size(elementAllocCnt, elementSize)));
765 
766  return size;
767 }
768 
769 /*
770  * Select an appropriate directory size for a hashtable with the given
771  * maximum number of entries.
772  * This is only needed for hashtables in shared memory, whose directories
773  * cannot be expanded dynamically.
774  * NB: assumes that all hash structure parameters have default values!
775  *
776  * XXX this had better agree with the behavior of init_htab()...
777  */
778 long
779 hash_select_dirsize(long num_entries)
780 {
781  long nBuckets,
782  nSegments,
783  nDirEntries;
784 
785  /* estimate number of buckets wanted */
786  nBuckets = next_pow2_long((num_entries - 1) / DEF_FFACTOR + 1);
787  /* # of segments needed for nBuckets */
788  nSegments = next_pow2_long((nBuckets - 1) / DEF_SEGSIZE + 1);
789  /* directory entries */
790  nDirEntries = DEF_DIRSIZE;
791  while (nDirEntries < nSegments)
792  nDirEntries <<= 1; /* dir_alloc doubles dsize at each call */
793 
794  return nDirEntries;
795 }
796 
797 /*
798  * Compute the required initial memory allocation for a shared-memory
799  * hashtable with the given parameters. We need space for the HASHHDR
800  * and for the (non expansible) directory.
801  */
802 Size
803 hash_get_shared_size(HASHCTL *info, int flags)
804 {
805  Assert(flags & HASH_DIRSIZE);
806  Assert(info->dsize == info->max_dsize);
807  return sizeof(HASHHDR) + info->dsize * sizeof(HASHSEGMENT);
808 }
809 
810 
811 /********************** DESTROY ROUTINES ************************/
812 
813 void
815 {
816  if (hashp != NULL)
817  {
818  /* allocation method must be one we know how to free, too */
819  Assert(hashp->alloc == DynaHashAlloc);
820  /* so this hashtable must have it's own context */
821  Assert(hashp->hcxt != NULL);
822 
823  hash_stats("destroy", hashp);
824 
825  /*
826  * Free everything by destroying the hash table's memory context.
827  */
828  MemoryContextDelete(hashp->hcxt);
829  }
830 }
831 
832 void
833 hash_stats(const char *where, HTAB *hashp)
834 {
835 #if HASH_STATISTICS
836  fprintf(stderr, "%s: this HTAB -- accesses %ld collisions %ld\n",
837  where, hashp->hctl->accesses, hashp->hctl->collisions);
838 
839  fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
840  hash_get_num_entries(hashp), (long) hashp->hctl->keysize,
841  hashp->hctl->max_bucket, hashp->hctl->nsegs);
842  fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
843  where, hash_accesses, hash_collisions);
844  fprintf(stderr, "hash_stats: total expansions %ld\n",
845  hash_expansions);
846 #endif
847 }
848 
849 /*******************************SEARCH ROUTINES *****************************/
850 
851 
852 /*
853  * get_hash_value -- exported routine to calculate a key's hash value
854  *
855  * We export this because for partitioned tables, callers need to compute
856  * the partition number (from the low-order bits of the hash value) before
857  * searching.
858  */
859 uint32
860 get_hash_value(HTAB *hashp, const void *keyPtr)
861 {
862  return hashp->hash(keyPtr, hashp->keysize);
863 }
864 
865 /* Convert a hash value to a bucket number */
866 static inline uint32
867 calc_bucket(HASHHDR *hctl, uint32 hash_val)
868 {
869  uint32 bucket;
870 
871  bucket = hash_val & hctl->high_mask;
872  if (bucket > hctl->max_bucket)
873  bucket = bucket & hctl->low_mask;
874 
875  return bucket;
876 }
877 
878 /*
879  * hash_search -- look up key in table and perform action
880  * hash_search_with_hash_value -- same, with key's hash value already computed
881  *
882  * action is one of:
883  * HASH_FIND: look up key in table
884  * HASH_ENTER: look up key in table, creating entry if not present
885  * HASH_ENTER_NULL: same, but return NULL if out of memory
886  * HASH_REMOVE: look up key in table, remove entry if present
887  *
888  * Return value is a pointer to the element found/entered/removed if any,
889  * or NULL if no match was found. (NB: in the case of the REMOVE action,
890  * the result is a dangling pointer that shouldn't be dereferenced!)
891  *
892  * HASH_ENTER will normally ereport a generic "out of memory" error if
893  * it is unable to create a new entry. The HASH_ENTER_NULL operation is
894  * the same except it will return NULL if out of memory. Note that
895  * HASH_ENTER_NULL cannot be used with the default palloc-based allocator,
896  * since palloc internally ereports on out-of-memory.
897  *
898  * If foundPtr isn't NULL, then *foundPtr is set true if we found an
899  * existing entry in the table, false otherwise. This is needed in the
900  * HASH_ENTER case, but is redundant with the return value otherwise.
901  *
902  * For hash_search_with_hash_value, the hashvalue parameter must have been
903  * calculated with get_hash_value().
904  */
905 void *
907  const void *keyPtr,
909  bool *foundPtr)
910 {
911  return hash_search_with_hash_value(hashp,
912  keyPtr,
913  hashp->hash(keyPtr, hashp->keysize),
914  action,
915  foundPtr);
916 }
917 
918 void *
920  const void *keyPtr,
921  uint32 hashvalue,
923  bool *foundPtr)
924 {
925  HASHHDR *hctl = hashp->hctl;
926  int freelist_idx = FREELIST_IDX(hctl, hashvalue);
927  Size keysize;
928  uint32 bucket;
929  long segment_num;
930  long segment_ndx;
931  HASHSEGMENT segp;
932  HASHBUCKET currBucket;
933  HASHBUCKET *prevBucketPtr;
934  HashCompareFunc match;
935 
936 #if HASH_STATISTICS
937  hash_accesses++;
938  hctl->accesses++;
939 #endif
940 
941  /*
942  * If inserting, check if it is time to split a bucket.
943  *
944  * NOTE: failure to expand table is not a fatal error, it just means we
945  * have to run at higher fill factor than we wanted. However, if we're
946  * using the palloc allocator then it will throw error anyway on
947  * out-of-memory, so we must do this before modifying the table.
948  */
949  if (action == HASH_ENTER || action == HASH_ENTER_NULL)
950  {
951  /*
952  * Can't split if running in partitioned mode, nor if frozen, nor if
953  * table is the subject of any active hash_seq_search scans. Strange
954  * order of these tests is to try to check cheaper conditions first.
955  */
956  if (!IS_PARTITIONED(hctl) && !hashp->frozen &&
957  hctl->freeList[0].nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
958  !has_seq_scans(hashp))
959  (void) expand_table(hashp);
960  }
961 
962  /*
963  * Do the initial lookup
964  */
965  bucket = calc_bucket(hctl, hashvalue);
966 
967  segment_num = bucket >> hashp->sshift;
968  segment_ndx = MOD(bucket, hashp->ssize);
969 
970  segp = hashp->dir[segment_num];
971 
972  if (segp == NULL)
973  hash_corrupted(hashp);
974 
975  prevBucketPtr = &segp[segment_ndx];
976  currBucket = *prevBucketPtr;
977 
978  /*
979  * Follow collision chain looking for matching key
980  */
981  match = hashp->match; /* save one fetch in inner loop */
982  keysize = hashp->keysize; /* ditto */
983 
984  while (currBucket != NULL)
985  {
986  if (currBucket->hashvalue == hashvalue &&
987  match(ELEMENTKEY(currBucket), keyPtr, keysize) == 0)
988  break;
989  prevBucketPtr = &(currBucket->link);
990  currBucket = *prevBucketPtr;
991 #if HASH_STATISTICS
992  hash_collisions++;
993  hctl->collisions++;
994 #endif
995  }
996 
997  if (foundPtr)
998  *foundPtr = (bool) (currBucket != NULL);
999 
1000  /*
1001  * OK, now what?
1002  */
1003  switch (action)
1004  {
1005  case HASH_FIND:
1006  if (currBucket != NULL)
1007  return (void *) ELEMENTKEY(currBucket);
1008  return NULL;
1009 
1010  case HASH_REMOVE:
1011  if (currBucket != NULL)
1012  {
1013  /* if partitioned, must lock to touch nentries and freeList */
1014  if (IS_PARTITIONED(hctl))
1015  SpinLockAcquire(&(hctl->freeList[freelist_idx].mutex));
1016 
1017  /* delete the record from the appropriate nentries counter. */
1018  Assert(hctl->freeList[freelist_idx].nentries > 0);
1019  hctl->freeList[freelist_idx].nentries--;
1020 
1021  /* remove record from hash bucket's chain. */
1022  *prevBucketPtr = currBucket->link;
1023 
1024  /* add the record to the appropriate freelist. */
1025  currBucket->link = hctl->freeList[freelist_idx].freeList;
1026  hctl->freeList[freelist_idx].freeList = currBucket;
1027 
1028  if (IS_PARTITIONED(hctl))
1029  SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
1030 
1031  /*
1032  * better hope the caller is synchronizing access to this
1033  * element, because someone else is going to reuse it the next
1034  * time something is added to the table
1035  */
1036  return (void *) ELEMENTKEY(currBucket);
1037  }
1038  return NULL;
1039 
1040  case HASH_ENTER_NULL:
1041  /* ENTER_NULL does not work with palloc-based allocator */
1042  Assert(hashp->alloc != DynaHashAlloc);
1043  /* FALL THRU */
1044 
1045  case HASH_ENTER:
1046  /* Return existing element if found, else create one */
1047  if (currBucket != NULL)
1048  return (void *) ELEMENTKEY(currBucket);
1049 
1050  /* disallow inserts if frozen */
1051  if (hashp->frozen)
1052  elog(ERROR, "cannot insert into frozen hashtable \"%s\"",
1053  hashp->tabname);
1054 
1055  currBucket = get_hash_entry(hashp, freelist_idx);
1056  if (currBucket == NULL)
1057  {
1058  /* out of memory */
1059  if (action == HASH_ENTER_NULL)
1060  return NULL;
1061  /* report a generic message */
1062  if (hashp->isshared)
1063  ereport(ERROR,
1064  (errcode(ERRCODE_OUT_OF_MEMORY),
1065  errmsg("out of shared memory")));
1066  else
1067  ereport(ERROR,
1068  (errcode(ERRCODE_OUT_OF_MEMORY),
1069  errmsg("out of memory")));
1070  }
1071 
1072  /* link into hashbucket chain */
1073  *prevBucketPtr = currBucket;
1074  currBucket->link = NULL;
1075 
1076  /* copy key into record */
1077  currBucket->hashvalue = hashvalue;
1078  hashp->keycopy(ELEMENTKEY(currBucket), keyPtr, keysize);
1079 
1080  /*
1081  * Caller is expected to fill the data field on return. DO NOT
1082  * insert any code that could possibly throw error here, as doing
1083  * so would leave the table entry incomplete and hence corrupt the
1084  * caller's data structure.
1085  */
1086 
1087  return (void *) ELEMENTKEY(currBucket);
1088  }
1089 
1090  elog(ERROR, "unrecognized hash action code: %d", (int) action);
1091 
1092  return NULL; /* keep compiler quiet */
1093 }
1094 
1095 /*
1096  * hash_update_hash_key -- change the hash key of an existing table entry
1097  *
1098  * This is equivalent to removing the entry, making a new entry, and copying
1099  * over its data, except that the entry never goes to the table's freelist.
1100  * Therefore this cannot suffer an out-of-memory failure, even if there are
1101  * other processes operating in other partitions of the hashtable.
1102  *
1103  * Returns true if successful, false if the requested new hash key is already
1104  * present. Throws error if the specified entry pointer isn't actually a
1105  * table member.
1106  *
1107  * NB: currently, there is no special case for old and new hash keys being
1108  * identical, which means we'll report false for that situation. This is
1109  * preferable for existing uses.
1110  *
1111  * NB: for a partitioned hashtable, caller must hold lock on both relevant
1112  * partitions, if the new hash key would belong to a different partition.
1113  */
1114 bool
1116  void *existingEntry,
1117  const void *newKeyPtr)
1118 {
1119  HASHELEMENT *existingElement = ELEMENT_FROM_KEY(existingEntry);
1120  HASHHDR *hctl = hashp->hctl;
1121  uint32 newhashvalue;
1122  Size keysize;
1123  uint32 bucket;
1124  uint32 newbucket;
1125  long segment_num;
1126  long segment_ndx;
1127  HASHSEGMENT segp;
1128  HASHBUCKET currBucket;
1129  HASHBUCKET *prevBucketPtr;
1130  HASHBUCKET *oldPrevPtr;
1131  HashCompareFunc match;
1132 
1133 #if HASH_STATISTICS
1134  hash_accesses++;
1135  hctl->accesses++;
1136 #endif
1137 
1138  /* disallow updates if frozen */
1139  if (hashp->frozen)
1140  elog(ERROR, "cannot update in frozen hashtable \"%s\"",
1141  hashp->tabname);
1142 
1143  /*
1144  * Lookup the existing element using its saved hash value. We need to do
1145  * this to be able to unlink it from its hash chain, but as a side benefit
1146  * we can verify the validity of the passed existingEntry pointer.
1147  */
1148  bucket = calc_bucket(hctl, existingElement->hashvalue);
1149 
1150  segment_num = bucket >> hashp->sshift;
1151  segment_ndx = MOD(bucket, hashp->ssize);
1152 
1153  segp = hashp->dir[segment_num];
1154 
1155  if (segp == NULL)
1156  hash_corrupted(hashp);
1157 
1158  prevBucketPtr = &segp[segment_ndx];
1159  currBucket = *prevBucketPtr;
1160 
1161  while (currBucket != NULL)
1162  {
1163  if (currBucket == existingElement)
1164  break;
1165  prevBucketPtr = &(currBucket->link);
1166  currBucket = *prevBucketPtr;
1167  }
1168 
1169  if (currBucket == NULL)
1170  elog(ERROR, "hash_update_hash_key argument is not in hashtable \"%s\"",
1171  hashp->tabname);
1172 
1173  oldPrevPtr = prevBucketPtr;
1174 
1175  /*
1176  * Now perform the equivalent of a HASH_ENTER operation to locate the hash
1177  * chain we want to put the entry into.
1178  */
1179  newhashvalue = hashp->hash(newKeyPtr, hashp->keysize);
1180 
1181  newbucket = calc_bucket(hctl, newhashvalue);
1182 
1183  segment_num = newbucket >> hashp->sshift;
1184  segment_ndx = MOD(newbucket, hashp->ssize);
1185 
1186  segp = hashp->dir[segment_num];
1187 
1188  if (segp == NULL)
1189  hash_corrupted(hashp);
1190 
1191  prevBucketPtr = &segp[segment_ndx];
1192  currBucket = *prevBucketPtr;
1193 
1194  /*
1195  * Follow collision chain looking for matching key
1196  */
1197  match = hashp->match; /* save one fetch in inner loop */
1198  keysize = hashp->keysize; /* ditto */
1199 
1200  while (currBucket != NULL)
1201  {
1202  if (currBucket->hashvalue == newhashvalue &&
1203  match(ELEMENTKEY(currBucket), newKeyPtr, keysize) == 0)
1204  break;
1205  prevBucketPtr = &(currBucket->link);
1206  currBucket = *prevBucketPtr;
1207 #if HASH_STATISTICS
1208  hash_collisions++;
1209  hctl->collisions++;
1210 #endif
1211  }
1212 
1213  if (currBucket != NULL)
1214  return false; /* collision with an existing entry */
1215 
1216  currBucket = existingElement;
1217 
1218  /*
1219  * If old and new hash values belong to the same bucket, we need not
1220  * change any chain links, and indeed should not since this simplistic
1221  * update will corrupt the list if currBucket is the last element. (We
1222  * cannot fall out earlier, however, since we need to scan the bucket to
1223  * check for duplicate keys.)
1224  */
1225  if (bucket != newbucket)
1226  {
1227  /* OK to remove record from old hash bucket's chain. */
1228  *oldPrevPtr = currBucket->link;
1229 
1230  /* link into new hashbucket chain */
1231  *prevBucketPtr = currBucket;
1232  currBucket->link = NULL;
1233  }
1234 
1235  /* copy new key into record */
1236  currBucket->hashvalue = newhashvalue;
1237  hashp->keycopy(ELEMENTKEY(currBucket), newKeyPtr, keysize);
1238 
1239  /* rest of record is untouched */
1240 
1241  return true;
1242 }
1243 
1244 /*
1245  * Allocate a new hashtable entry if possible; return NULL if out of memory.
1246  * (Or, if the underlying space allocator throws error for out-of-memory,
1247  * we won't return at all.)
1248  */
1249 static HASHBUCKET
1250 get_hash_entry(HTAB *hashp, int freelist_idx)
1251 {
1252  HASHHDR *hctl = hashp->hctl;
1253  HASHBUCKET newElement;
1254 
1255  for (;;)
1256  {
1257  /* if partitioned, must lock to touch nentries and freeList */
1258  if (IS_PARTITIONED(hctl))
1259  SpinLockAcquire(&hctl->freeList[freelist_idx].mutex);
1260 
1261  /* try to get an entry from the freelist */
1262  newElement = hctl->freeList[freelist_idx].freeList;
1263 
1264  if (newElement != NULL)
1265  break;
1266 
1267  if (IS_PARTITIONED(hctl))
1268  SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
1269 
1270  /*
1271  * No free elements in this freelist. In a partitioned table, there
1272  * might be entries in other freelists, but to reduce contention we
1273  * prefer to first try to get another chunk of buckets from the main
1274  * shmem allocator. If that fails, though, we *MUST* root through all
1275  * the other freelists before giving up. There are multiple callers
1276  * that assume that they can allocate every element in the initially
1277  * requested table size, or that deleting an element guarantees they
1278  * can insert a new element, even if shared memory is entirely full.
1279  * Failing because the needed element is in a different freelist is
1280  * not acceptable.
1281  */
1282  if (!element_alloc(hashp, hctl->nelem_alloc, freelist_idx))
1283  {
1284  int borrow_from_idx;
1285 
1286  if (!IS_PARTITIONED(hctl))
1287  return NULL; /* out of memory */
1288 
1289  /* try to borrow element from another freelist */
1290  borrow_from_idx = freelist_idx;
1291  for (;;)
1292  {
1293  borrow_from_idx = (borrow_from_idx + 1) % NUM_FREELISTS;
1294  if (borrow_from_idx == freelist_idx)
1295  break; /* examined all freelists, fail */
1296 
1297  SpinLockAcquire(&(hctl->freeList[borrow_from_idx].mutex));
1298  newElement = hctl->freeList[borrow_from_idx].freeList;
1299 
1300  if (newElement != NULL)
1301  {
1302  hctl->freeList[borrow_from_idx].freeList = newElement->link;
1303  SpinLockRelease(&(hctl->freeList[borrow_from_idx].mutex));
1304 
1305  /* careful: count the new element in its proper freelist */
1306  SpinLockAcquire(&hctl->freeList[freelist_idx].mutex);
1307  hctl->freeList[freelist_idx].nentries++;
1308  SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
1309 
1310  return newElement;
1311  }
1312 
1313  SpinLockRelease(&(hctl->freeList[borrow_from_idx].mutex));
1314  }
1315 
1316  /* no elements available to borrow either, so out of memory */
1317  return NULL;
1318  }
1319  }
1320 
1321  /* remove entry from freelist, bump nentries */
1322  hctl->freeList[freelist_idx].freeList = newElement->link;
1323  hctl->freeList[freelist_idx].nentries++;
1324 
1325  if (IS_PARTITIONED(hctl))
1326  SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
1327 
1328  return newElement;
1329 }
1330 
1331 /*
1332  * hash_get_num_entries -- get the number of entries in a hashtable
1333  */
1334 long
1336 {
1337  int i;
1338  long sum = hashp->hctl->freeList[0].nentries;
1339 
1340  /*
1341  * We currently don't bother with acquiring the mutexes; it's only
1342  * sensible to call this function if you've got lock on all partitions of
1343  * the table.
1344  */
1345  if (IS_PARTITIONED(hashp->hctl))
1346  {
1347  for (i = 1; i < NUM_FREELISTS; i++)
1348  sum += hashp->hctl->freeList[i].nentries;
1349  }
1350 
1351  return sum;
1352 }
1353 
1354 /*
1355  * hash_seq_init/_search/_term
1356  * Sequentially search through hash table and return
1357  * all the elements one by one, return NULL when no more.
1358  *
1359  * hash_seq_term should be called if and only if the scan is abandoned before
1360  * completion; if hash_seq_search returns NULL then it has already done the
1361  * end-of-scan cleanup.
1362  *
1363  * NOTE: caller may delete the returned element before continuing the scan.
1364  * However, deleting any other element while the scan is in progress is
1365  * UNDEFINED (it might be the one that curIndex is pointing at!). Also,
1366  * if elements are added to the table while the scan is in progress, it is
1367  * unspecified whether they will be visited by the scan or not.
1368  *
1369  * NOTE: it is possible to use hash_seq_init/hash_seq_search without any
1370  * worry about hash_seq_term cleanup, if the hashtable is first locked against
1371  * further insertions by calling hash_freeze.
1372  *
1373  * NOTE: to use this with a partitioned hashtable, caller had better hold
1374  * at least shared lock on all partitions of the table throughout the scan!
1375  * We can cope with insertions or deletions by our own backend, but *not*
1376  * with concurrent insertions or deletions by another.
1377  */
1378 void
1380 {
1381  status->hashp = hashp;
1382  status->curBucket = 0;
1383  status->curEntry = NULL;
1384  if (!hashp->frozen)
1385  register_seq_scan(hashp);
1386 }
1387 
1388 void *
1390 {
1391  HTAB *hashp;
1392  HASHHDR *hctl;
1394  long ssize;
1395  long segment_num;
1396  long segment_ndx;
1397  HASHSEGMENT segp;
1398  uint32 curBucket;
1399  HASHELEMENT *curElem;
1400 
1401  if ((curElem = status->curEntry) != NULL)
1402  {
1403  /* Continuing scan of curBucket... */
1404  status->curEntry = curElem->link;
1405  if (status->curEntry == NULL) /* end of this bucket */
1406  ++status->curBucket;
1407  return (void *) ELEMENTKEY(curElem);
1408  }
1409 
1410  /*
1411  * Search for next nonempty bucket starting at curBucket.
1412  */
1413  curBucket = status->curBucket;
1414  hashp = status->hashp;
1415  hctl = hashp->hctl;
1416  ssize = hashp->ssize;
1417  max_bucket = hctl->max_bucket;
1418 
1419  if (curBucket > max_bucket)
1420  {
1421  hash_seq_term(status);
1422  return NULL; /* search is done */
1423  }
1424 
1425  /*
1426  * first find the right segment in the table directory.
1427  */
1428  segment_num = curBucket >> hashp->sshift;
1429  segment_ndx = MOD(curBucket, ssize);
1430 
1431  segp = hashp->dir[segment_num];
1432 
1433  /*
1434  * Pick up the first item in this bucket's chain. If chain is not empty
1435  * we can begin searching it. Otherwise we have to advance to find the
1436  * next nonempty bucket. We try to optimize that case since searching a
1437  * near-empty hashtable has to iterate this loop a lot.
1438  */
1439  while ((curElem = segp[segment_ndx]) == NULL)
1440  {
1441  /* empty bucket, advance to next */
1442  if (++curBucket > max_bucket)
1443  {
1444  status->curBucket = curBucket;
1445  hash_seq_term(status);
1446  return NULL; /* search is done */
1447  }
1448  if (++segment_ndx >= ssize)
1449  {
1450  segment_num++;
1451  segment_ndx = 0;
1452  segp = hashp->dir[segment_num];
1453  }
1454  }
1455 
1456  /* Begin scan of curBucket... */
1457  status->curEntry = curElem->link;
1458  if (status->curEntry == NULL) /* end of this bucket */
1459  ++curBucket;
1460  status->curBucket = curBucket;
1461  return (void *) ELEMENTKEY(curElem);
1462 }
1463 
1464 void
1466 {
1467  if (!status->hashp->frozen)
1468  deregister_seq_scan(status->hashp);
1469 }
1470 
1471 /*
1472  * hash_freeze
1473  * Freeze a hashtable against future insertions (deletions are
1474  * still allowed)
1475  *
1476  * The reason for doing this is that by preventing any more bucket splits,
1477  * we no longer need to worry about registering hash_seq_search scans,
1478  * and thus caller need not be careful about ensuring hash_seq_term gets
1479  * called at the right times.
1480  *
1481  * Multiple calls to hash_freeze() are allowed, but you can't freeze a table
1482  * with active scans (since hash_seq_term would then do the wrong thing).
1483  */
1484 void
1486 {
1487  if (hashp->isshared)
1488  elog(ERROR, "cannot freeze shared hashtable \"%s\"", hashp->tabname);
1489  if (!hashp->frozen && has_seq_scans(hashp))
1490  elog(ERROR, "cannot freeze hashtable \"%s\" because it has active scans",
1491  hashp->tabname);
1492  hashp->frozen = true;
1493 }
1494 
1495 
1496 /********************************* UTILITIES ************************/
1497 
1498 /*
1499  * Expand the table by adding one more hash bucket.
1500  */
1501 static bool
1503 {
1504  HASHHDR *hctl = hashp->hctl;
1505  HASHSEGMENT old_seg,
1506  new_seg;
1507  long old_bucket,
1508  new_bucket;
1509  long new_segnum,
1510  new_segndx;
1511  long old_segnum,
1512  old_segndx;
1513  HASHBUCKET *oldlink,
1514  *newlink;
1515  HASHBUCKET currElement,
1516  nextElement;
1517 
1518  Assert(!IS_PARTITIONED(hctl));
1519 
1520 #ifdef HASH_STATISTICS
1521  hash_expansions++;
1522 #endif
1523 
1524  new_bucket = hctl->max_bucket + 1;
1525  new_segnum = new_bucket >> hashp->sshift;
1526  new_segndx = MOD(new_bucket, hashp->ssize);
1527 
1528  if (new_segnum >= hctl->nsegs)
1529  {
1530  /* Allocate new segment if necessary -- could fail if dir full */
1531  if (new_segnum >= hctl->dsize)
1532  if (!dir_realloc(hashp))
1533  return false;
1534  if (!(hashp->dir[new_segnum] = seg_alloc(hashp)))
1535  return false;
1536  hctl->nsegs++;
1537  }
1538 
1539  /* OK, we created a new bucket */
1540  hctl->max_bucket++;
1541 
1542  /*
1543  * *Before* changing masks, find old bucket corresponding to same hash
1544  * values; values in that bucket may need to be relocated to new bucket.
1545  * Note that new_bucket is certainly larger than low_mask at this point,
1546  * so we can skip the first step of the regular hash mask calc.
1547  */
1548  old_bucket = (new_bucket & hctl->low_mask);
1549 
1550  /*
1551  * If we crossed a power of 2, readjust masks.
1552  */
1553  if ((uint32) new_bucket > hctl->high_mask)
1554  {
1555  hctl->low_mask = hctl->high_mask;
1556  hctl->high_mask = (uint32) new_bucket | hctl->low_mask;
1557  }
1558 
1559  /*
1560  * Relocate records to the new bucket. NOTE: because of the way the hash
1561  * masking is done in calc_bucket, only one old bucket can need to be
1562  * split at this point. With a different way of reducing the hash value,
1563  * that might not be true!
1564  */
1565  old_segnum = old_bucket >> hashp->sshift;
1566  old_segndx = MOD(old_bucket, hashp->ssize);
1567 
1568  old_seg = hashp->dir[old_segnum];
1569  new_seg = hashp->dir[new_segnum];
1570 
1571  oldlink = &old_seg[old_segndx];
1572  newlink = &new_seg[new_segndx];
1573 
1574  for (currElement = *oldlink;
1575  currElement != NULL;
1576  currElement = nextElement)
1577  {
1578  nextElement = currElement->link;
1579  if ((long) calc_bucket(hctl, currElement->hashvalue) == old_bucket)
1580  {
1581  *oldlink = currElement;
1582  oldlink = &currElement->link;
1583  }
1584  else
1585  {
1586  *newlink = currElement;
1587  newlink = &currElement->link;
1588  }
1589  }
1590  /* don't forget to terminate the rebuilt hash chains... */
1591  *oldlink = NULL;
1592  *newlink = NULL;
1593 
1594  return true;
1595 }
1596 
1597 
1598 static bool
1600 {
1601  HASHSEGMENT *p;
1602  HASHSEGMENT *old_p;
1603  long new_dsize;
1604  long old_dirsize;
1605  long new_dirsize;
1606 
1607  if (hashp->hctl->max_dsize != NO_MAX_DSIZE)
1608  return false;
1609 
1610  /* Reallocate directory */
1611  new_dsize = hashp->hctl->dsize << 1;
1612  old_dirsize = hashp->hctl->dsize * sizeof(HASHSEGMENT);
1613  new_dirsize = new_dsize * sizeof(HASHSEGMENT);
1614 
1615  old_p = hashp->dir;
1616  CurrentDynaHashCxt = hashp->hcxt;
1617  p = (HASHSEGMENT *) hashp->alloc((Size) new_dirsize);
1618 
1619  if (p != NULL)
1620  {
1621  memcpy(p, old_p, old_dirsize);
1622  MemSet(((char *) p) + old_dirsize, 0, new_dirsize - old_dirsize);
1623  hashp->dir = p;
1624  hashp->hctl->dsize = new_dsize;
1625 
1626  /* XXX assume the allocator is palloc, so we know how to free */
1627  Assert(hashp->alloc == DynaHashAlloc);
1628  pfree(old_p);
1629 
1630  return true;
1631  }
1632 
1633  return false;
1634 }
1635 
1636 
1637 static HASHSEGMENT
1639 {
1640  HASHSEGMENT segp;
1641 
1642  CurrentDynaHashCxt = hashp->hcxt;
1643  segp = (HASHSEGMENT) hashp->alloc(sizeof(HASHBUCKET) * hashp->ssize);
1644 
1645  if (!segp)
1646  return NULL;
1647 
1648  MemSet(segp, 0, sizeof(HASHBUCKET) * hashp->ssize);
1649 
1650  return segp;
1651 }
1652 
1653 /*
1654  * allocate some new elements and link them into the indicated free list
1655  */
1656 static bool
1657 element_alloc(HTAB *hashp, int nelem, int freelist_idx)
1658 {
1659  HASHHDR *hctl = hashp->hctl;
1660  Size elementSize;
1661  HASHELEMENT *firstElement;
1662  HASHELEMENT *tmpElement;
1663  HASHELEMENT *prevElement;
1664  int i;
1665 
1666  if (hashp->isfixed)
1667  return false;
1668 
1669  /* Each element has a HASHELEMENT header plus user data. */
1670  elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctl->entrysize);
1671 
1672  CurrentDynaHashCxt = hashp->hcxt;
1673  firstElement = (HASHELEMENT *) hashp->alloc(nelem * elementSize);
1674 
1675  if (!firstElement)
1676  return false;
1677 
1678  /* prepare to link all the new entries into the freelist */
1679  prevElement = NULL;
1680  tmpElement = firstElement;
1681  for (i = 0; i < nelem; i++)
1682  {
1683  tmpElement->link = prevElement;
1684  prevElement = tmpElement;
1685  tmpElement = (HASHELEMENT *) (((char *) tmpElement) + elementSize);
1686  }
1687 
1688  /* if partitioned, must lock to touch freeList */
1689  if (IS_PARTITIONED(hctl))
1690  SpinLockAcquire(&hctl->freeList[freelist_idx].mutex);
1691 
1692  /* freelist could be nonempty if two backends did this concurrently */
1693  firstElement->link = hctl->freeList[freelist_idx].freeList;
1694  hctl->freeList[freelist_idx].freeList = prevElement;
1695 
1696  if (IS_PARTITIONED(hctl))
1697  SpinLockRelease(&hctl->freeList[freelist_idx].mutex);
1698 
1699  return true;
1700 }
1701 
1702 /* complain when we have detected a corrupted hashtable */
1703 static void
1705 {
1706  /*
1707  * If the corruption is in a shared hashtable, we'd better force a
1708  * systemwide restart. Otherwise, just shut down this one backend.
1709  */
1710  if (hashp->isshared)
1711  elog(PANIC, "hash table \"%s\" corrupted", hashp->tabname);
1712  else
1713  elog(FATAL, "hash table \"%s\" corrupted", hashp->tabname);
1714 }
1715 
1716 /* calculate ceil(log base 2) of num */
1717 int
1718 my_log2(long num)
1719 {
1720  int i;
1721  long limit;
1722 
1723  /* guard against too-large input, which would put us into infinite loop */
1724  if (num > LONG_MAX / 2)
1725  num = LONG_MAX / 2;
1726 
1727  for (i = 0, limit = 1; limit < num; i++, limit <<= 1)
1728  ;
1729  return i;
1730 }
1731 
1732 /* calculate first power of 2 >= num, bounded to what will fit in a long */
1733 static long
1735 {
1736  /* my_log2's internal range check is sufficient */
1737  return 1L << my_log2(num);
1738 }
1739 
1740 /* calculate first power of 2 >= num, bounded to what will fit in an int */
1741 static int
1742 next_pow2_int(long num)
1743 {
1744  if (num > INT_MAX / 2)
1745  num = INT_MAX / 2;
1746  return 1 << my_log2(num);
1747 }
1748 
1749 
1750 /************************* SEQ SCAN TRACKING ************************/
1751 
1752 /*
1753  * We track active hash_seq_search scans here. The need for this mechanism
1754  * comes from the fact that a scan will get confused if a bucket split occurs
1755  * while it's in progress: it might visit entries twice, or even miss some
1756  * entirely (if it's partway through the same bucket that splits). Hence
1757  * we want to inhibit bucket splits if there are any active scans on the
1758  * table being inserted into. This is a fairly rare case in current usage,
1759  * so just postponing the split until the next insertion seems sufficient.
1760  *
1761  * Given present usages of the function, only a few scans are likely to be
1762  * open concurrently; so a finite-size stack of open scans seems sufficient,
1763  * and we don't worry that linear search is too slow. Note that we do
1764  * allow multiple scans of the same hashtable to be open concurrently.
1765  *
1766  * This mechanism can support concurrent scan and insertion in a shared
1767  * hashtable if it's the same backend doing both. It would fail otherwise,
1768  * but locking reasons seem to preclude any such scenario anyway, so we don't
1769  * worry.
1770  *
1771  * This arrangement is reasonably robust if a transient hashtable is deleted
1772  * without notifying us. The absolute worst case is we might inhibit splits
1773  * in another table created later at exactly the same address. We will give
1774  * a warning at transaction end for reference leaks, so any bugs leading to
1775  * lack of notification should be easy to catch.
1776  */
1777 
1778 #define MAX_SEQ_SCANS 100
1779 
1780 static HTAB *seq_scan_tables[MAX_SEQ_SCANS]; /* tables being scanned */
1781 static int seq_scan_level[MAX_SEQ_SCANS]; /* subtransaction nest level */
1782 static int num_seq_scans = 0;
1783 
1784 
1785 /* Register a table as having an active hash_seq_search scan */
1786 static void
1788 {
1790  elog(ERROR, "too many active hash_seq_search scans, cannot start one on \"%s\"",
1791  hashp->tabname);
1792  seq_scan_tables[num_seq_scans] = hashp;
1794  num_seq_scans++;
1795 }
1796 
1797 /* Deregister an active scan */
1798 static void
1800 {
1801  int i;
1802 
1803  /* Search backward since it's most likely at the stack top */
1804  for (i = num_seq_scans - 1; i >= 0; i--)
1805  {
1806  if (seq_scan_tables[i] == hashp)
1807  {
1808  seq_scan_tables[i] = seq_scan_tables[num_seq_scans - 1];
1810  num_seq_scans--;
1811  return;
1812  }
1813  }
1814  elog(ERROR, "no hash_seq_search scan for hash table \"%s\"",
1815  hashp->tabname);
1816 }
1817 
1818 /* Check if a table has any active scan */
1819 static bool
1821 {
1822  int i;
1823 
1824  for (i = 0; i < num_seq_scans; i++)
1825  {
1826  if (seq_scan_tables[i] == hashp)
1827  return true;
1828  }
1829  return false;
1830 }
1831 
1832 /* Clean up any open scans at end of transaction */
1833 void
1834 AtEOXact_HashTables(bool isCommit)
1835 {
1836  /*
1837  * During abort cleanup, open scans are expected; just silently clean 'em
1838  * out. An open scan at commit means someone forgot a hash_seq_term()
1839  * call, so complain.
1840  *
1841  * Note: it's tempting to try to print the tabname here, but refrain for
1842  * fear of touching deallocated memory. This isn't a user-facing message
1843  * anyway, so it needn't be pretty.
1844  */
1845  if (isCommit)
1846  {
1847  int i;
1848 
1849  for (i = 0; i < num_seq_scans; i++)
1850  {
1851  elog(WARNING, "leaked hash_seq_search scan for hash table %p",
1852  seq_scan_tables[i]);
1853  }
1854  }
1855  num_seq_scans = 0;
1856 }
1857 
1858 /* Clean up any open scans at end of subtransaction */
1859 void
1860 AtEOSubXact_HashTables(bool isCommit, int nestDepth)
1861 {
1862  int i;
1863 
1864  /*
1865  * Search backward to make cleanup easy. Note we must check all entries,
1866  * not only those at the end of the array, because deletion technique
1867  * doesn't keep them in order.
1868  */
1869  for (i = num_seq_scans - 1; i >= 0; i--)
1870  {
1871  if (seq_scan_level[i] >= nestDepth)
1872  {
1873  if (isCommit)
1874  elog(WARNING, "leaked hash_seq_search scan for hash table %p",
1875  seq_scan_tables[i]);
1876  seq_scan_tables[i] = seq_scan_tables[num_seq_scans - 1];
1878  num_seq_scans--;
1879  }
1880  }
1881 }
void * hash_search_with_hash_value(HTAB *hashp, const void *keyPtr, uint32 hashvalue, HASHACTION action, bool *foundPtr)
Definition: dynahash.c:919
static int seq_scan_level[MAX_SEQ_SCANS]
Definition: dynahash.c:1781
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Definition: hsearch.h:29
Size keysize
Definition: dynahash.c:179
int slock_t
Definition: s_lock.h:912
Size keysize
Definition: dynahash.c:225
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Definition: dynahash.c:172
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Definition: dynahash.c:814
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Definition: mcxt.c:211
#define HASH_CONTEXT
Definition: hsearch.h:93
#define HASH_ELEM
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uint32 max_bucket
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Definition: hsearch.h:78
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Size entrysize
Definition: dynahash.c:180
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#define IS_PARTITIONED(hctl)
Definition: dynahash.c:199
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Definition: hashfn.c:34
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Definition: spin.h:60
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#define ELEMENTKEY(helem)
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Definition: dynahash.c:181
void AtEOSubXact_HashTables(bool isCommit, int nestDepth)
Definition: dynahash.c:1860
Size entrysize
Definition: hsearch.h:73
#define NUM_FREELISTS
Definition: dynahash.c:116
void hash_stats(const char *where, HTAB *hashp)
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HASHELEMENT * curEntry
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Definition: dynahash.c:176
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Definition: dynahash.c:906
#define HASH_SHARED_MEM
Definition: hsearch.h:94
static int string_compare(const char *key1, const char *key2, Size keysize)
Definition: dynahash.c:293
static HASHBUCKET get_hash_entry(HTAB *hashp, int freelist_idx)
Definition: dynahash.c:1250
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Definition: hsearch.h:69
#define PANIC
Definition: elog.h:53
uint32 uint32_hash(const void *key, Size keysize)
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Definition: hsearch.h:83
#define HASH_ATTACH
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Definition: spin.h:62
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Definition: dynahash.c:860
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Definition: hsearch.h:70
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Definition: mcxt.c:1031
HASHBUCKET * HASHSEGMENT
Definition: dynahash.c:122
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Definition: dynahash.c:226
#define ERROR
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int sshift
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Definition: memutils.h:192
#define DEF_SEGSIZE_SHIFT
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Definition: hsearch.h:77
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Definition: dynahash.c:210
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Definition: dynahash.c:1820
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unsigned int uint32
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HASHELEMENT * HASHBUCKET
Definition: dynahash.c:119
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Definition: hsearch.h:114
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Definition: memutils.h:170
#define WARNING
Definition: elog.h:40
HashCompareFunc match
Definition: dynahash.c:213
Size hash_estimate_size(long num_entries, Size entrysize)
Definition: dynahash.c:732
static int next_pow2_int(long num)
Definition: dynahash.c:1742
bool isshared
Definition: dynahash.c:218
#define SpinLockRelease(lock)
Definition: spin.h:64
#define MAX_SEQ_SCANS
Definition: dynahash.c:1778
#define HASH_BLOBS
Definition: hsearch.h:88
bool frozen
Definition: dynahash.c:222
Size mul_size(Size s1, Size s2)
Definition: shmem.c:492
static int num_seq_scans
Definition: dynahash.c:1782
static HTAB * seq_scan_tables[MAX_SEQ_SCANS]
Definition: dynahash.c:1780
uint32 tag_hash(const void *key, Size keysize)
Definition: hashfn.c:52
HTAB * hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
Definition: dynahash.c:316
long ssize
Definition: dynahash.c:184
Size add_size(Size s1, Size s2)
Definition: shmem.c:475
FreeListData freeList[NUM_FREELISTS]
Definition: dynahash.c:168
static void deregister_seq_scan(HTAB *hashp)
Definition: dynahash.c:1799
Size keysize
Definition: hsearch.h:72
void *(* HashCopyFunc)(void *dest, const void *src, Size keysize)
Definition: hsearch.h:37
HashCompareFunc match
Definition: hsearch.h:75
MemoryContext hcxt
Definition: dynahash.c:216
long hash_select_dirsize(long num_entries)
Definition: dynahash.c:779
HashCopyFunc keycopy
Definition: dynahash.c:214
#define HASH_SEGMENT
Definition: hsearch.h:84
int GetCurrentTransactionNestLevel(void)
Definition: xact.c:753
size_t strlcpy(char *dst, const char *src, size_t siz)
Definition: strlcpy.c:45
#define MemoryContextIsValid(context)
Definition: memnodes.h:101
static void register_seq_scan(HTAB *hashp)
Definition: dynahash.c:1787
#define Assert(condition)
Definition: c.h:699
int nelem_alloc
Definition: dynahash.c:186
void *(* HashAllocFunc)(Size request)
Definition: hsearch.h:44
#define HASH_COMPARE
Definition: hsearch.h:90
size_t Size
Definition: c.h:433
void hash_freeze(HTAB *hashp)
Definition: dynahash.c:1485
static HASHSEGMENT seg_alloc(HTAB *hashp)
Definition: dynahash.c:1638
#define MAXALIGN(LEN)
Definition: c.h:652
void MemoryContextSetIdentifier(MemoryContext context, const char *id)
Definition: mcxt.c:329
Size hash_get_shared_size(HASHCTL *info, int flags)
Definition: dynahash.c:803
static bool expand_table(HTAB *hashp)
Definition: dynahash.c:1502
bool hash_update_hash_key(HTAB *hashp, void *existingEntry, const void *newKeyPtr)
Definition: dynahash.c:1115
HASHHDR * hctl
Definition: hsearch.h:79
void * hash_seq_search(HASH_SEQ_STATUS *status)
Definition: dynahash.c:1389
long ffactor
Definition: hsearch.h:71
void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
Definition: dynahash.c:1379
char * tabname
Definition: dynahash.c:217
#define HASH_FIXED_SIZE
Definition: hsearch.h:96
bool isfixed
Definition: dynahash.c:219
#define HASH_FFACTOR
Definition: hsearch.h:86
static void * DynaHashAlloc(Size size)
Definition: dynahash.c:278
#define HASH_DIRSIZE
Definition: hsearch.h:85
int errmsg(const char *fmt,...)
Definition: elog.c:797
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:771
struct HASHELEMENT * link
Definition: hsearch.h:53
static int choose_nelem_alloc(Size entrysize)
Definition: dynahash.c:603
static MemoryContext CurrentDynaHashCxt
Definition: dynahash.c:275
int i
#define HASH_ALLOC
Definition: hsearch.h:92
HASHELEMENT * freeList
Definition: dynahash.c:145
HASHSEGMENT * dir
Definition: dynahash.c:211
#define elog
Definition: elog.h:219
static bool element_alloc(HTAB *hashp, int nelem, int freelist_idx)
Definition: dynahash.c:1657
#define FREELIST_IDX(hctl, hashcode)
Definition: dynahash.c:201
void AtEOXact_HashTables(bool isCommit)
Definition: dynahash.c:1834
static void static void status(const char *fmt,...) pg_attribute_printf(1
Definition: pg_regress.c:225
int sshift
Definition: dynahash.c:185
static bool dir_realloc(HTAB *hashp)
Definition: dynahash.c:1599
#define DEF_FFACTOR
Definition: dynahash.c:113
#define DEF_SEGSIZE
Definition: dynahash.c:110
void hash_seq_term(HASH_SEQ_STATUS *status)
Definition: dynahash.c:1465
uint32 hashvalue
Definition: hsearch.h:54
HASHACTION
Definition: hsearch.h:103
HashValueFunc hash
Definition: hsearch.h:74
#define HASH_FUNCTION
Definition: hsearch.h:89
#define DEF_DIRSIZE
Definition: dynahash.c:112
long nsegs
Definition: dynahash.c:173