*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.58 2004/12/31 22:01:37 pgsql Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.59 2005/05/06 00:19:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/*
- * memory allocation routines
+ * memory allocation support
*/
-static MemoryContext DynaHashCxt = NULL;
static MemoryContext CurrentDynaHashCxt = NULL;
static void *
return MemoryContextAlloc(CurrentDynaHashCxt, size);
}
-#define MEM_ALLOC DynaHashAlloc
-#undef MEM_FREE /* already in windows header files */
-#define MEM_FREE pfree
-
#if HASH_STATISTICS
static long hash_accesses,
/************************** CREATE ROUTINES **********************/
+/*
+ * hash_create -- create a new dynamic hash table
+ *
+ * tabname: a name for the table (for debugging purposes)
+ * nelem: maximum number of elements expected
+ * *info: additional table parameters, as indicated by flags
+ * flags: bitmask indicating which parameters to take from *info
+ *
+ * Note: for a shared-memory hashtable, nelem needs to be a pretty good
+ * estimate, since we can't expand the table on the fly. But an unshared
+ * hashtable can be expanded on-the-fly, so it's better for nelem to be
+ * on the small side and let the table grow if it's exceeded. An overly
+ * large nelem will penalize hash_seq_search speed without buying much.
+ */
HTAB *
hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
{
HTAB *hashp;
HASHHDR *hctl;
- /* First time through, create a memory context for hash tables */
- if (!DynaHashCxt)
- DynaHashCxt = AllocSetContextCreate(TopMemoryContext,
- "DynaHash",
- ALLOCSET_DEFAULT_MINSIZE,
- ALLOCSET_DEFAULT_INITSIZE,
- ALLOCSET_DEFAULT_MAXSIZE);
-
- /* Select allocation context for this hash table */
- if (flags & HASH_CONTEXT)
- CurrentDynaHashCxt = info->hcxt;
+ /*
+ * For shared hash tables, we have a local hash header (HTAB struct)
+ * that we allocate in TopMemoryContext; all else is in shared memory.
+ *
+ * For non-shared hash tables, everything including the hash header
+ * is in a memory context created specially for the hash table ---
+ * this makes hash_destroy very simple. The memory context is made
+ * a child of either a context specified by the caller, or
+ * TopMemoryContext if nothing is specified.
+ */
+ if (flags & HASH_SHARED_MEM)
+ {
+ /* Set up to allocate the hash header */
+ CurrentDynaHashCxt = TopMemoryContext;
+ }
else
- CurrentDynaHashCxt = DynaHashCxt;
+ {
+ /* Create the hash table's private memory context */
+ if (flags & HASH_CONTEXT)
+ CurrentDynaHashCxt = info->hcxt;
+ else
+ CurrentDynaHashCxt = TopMemoryContext;
+ CurrentDynaHashCxt = AllocSetContextCreate(CurrentDynaHashCxt,
+ tabname,
+ ALLOCSET_DEFAULT_MINSIZE,
+ ALLOCSET_DEFAULT_INITSIZE,
+ ALLOCSET_DEFAULT_MAXSIZE);
+ }
- /* Initialize the hash header */
- hashp = (HTAB *) MEM_ALLOC(sizeof(HTAB));
+ /* Initialize the hash header, plus a copy of the table name */
+ hashp = (HTAB *) DynaHashAlloc(sizeof(HTAB) + strlen(tabname) + 1);
MemSet(hashp, 0, sizeof(HTAB));
- hashp->tabname = (char *) MEM_ALLOC(strlen(tabname) + 1);
+ hashp->tabname = (char *) (hashp + 1);
strcpy(hashp->tabname, tabname);
if (flags & HASH_FUNCTION)
else
hashp->match = memcmp;
+ if (flags & HASH_ALLOC)
+ hashp->alloc = info->alloc;
+ else
+ hashp->alloc = DynaHashAlloc;
+
if (flags & HASH_SHARED_MEM)
{
/*
*/
hashp->hctl = info->hctl;
hashp->dir = info->dir;
- hashp->alloc = info->alloc;
hashp->hcxt = NULL;
hashp->isshared = true;
/* setup hash table defaults */
hashp->hctl = NULL;
hashp->dir = NULL;
- hashp->alloc = MEM_ALLOC;
hashp->hcxt = CurrentDynaHashCxt;
hashp->isshared = false;
}
*/
if (flags & HASH_ELEM)
{
+ Assert(info->entrysize >= info->keysize);
hctl->keysize = info->keysize;
hctl->entrysize = info->entrysize;
}
- if (flags & HASH_ALLOC)
- hashp->alloc = info->alloc;
- else
- {
- /* remaining hash table structures live in child of given context */
- hashp->hcxt = AllocSetContextCreate(CurrentDynaHashCxt,
- tabname,
- ALLOCSET_DEFAULT_MINSIZE,
- ALLOCSET_DEFAULT_INITSIZE,
- ALLOCSET_DEFAULT_MAXSIZE);
- CurrentDynaHashCxt = hashp->hcxt;
- }
-
/* Build the hash directory structure */
if (!init_htab(hashp, nelem))
{
if (hashp != NULL)
{
/* allocation method must be one we know how to free, too */
- Assert(hashp->alloc == MEM_ALLOC);
+ Assert(hashp->alloc == DynaHashAlloc);
/* so this hashtable must have it's own context */
Assert(hashp->hcxt != NULL);
hash_stats("destroy", hashp);
/*
- * Free buckets, dir etc. by destroying the hash table's memory
- * context.
+ * Free everything by destroying the hash table's memory context.
*/
MemoryContextDelete(hashp->hcxt);
-
- /*
- * Free the HTAB and control structure, which are allocated in the
- * parent context (DynaHashCxt or the context given by the caller
- * of hash_create()).
- */
- MEM_FREE(hashp->hctl);
- MEM_FREE(hashp->tabname);
- MEM_FREE(hashp);
}
}
void *
hash_seq_search(HASH_SEQ_STATUS *status)
{
- HTAB *hashp = status->hashp;
- HASHHDR *hctl = hashp->hctl;
+ HTAB *hashp;
+ HASHHDR *hctl;
+ uint32 max_bucket;
+ long ssize;
+ long segment_num;
+ long segment_ndx;
+ HASHSEGMENT segp;
+ uint32 curBucket;
+ HASHELEMENT *curElem;
- while (status->curBucket <= hctl->max_bucket)
+ if ((curElem = status->curEntry) != NULL)
{
- long segment_num;
- long segment_ndx;
- HASHSEGMENT segp;
+ /* Continuing scan of curBucket... */
+ status->curEntry = curElem->link;
+ if (status->curEntry == NULL) /* end of this bucket */
+ ++status->curBucket;
+ return (void *) ELEMENTKEY(curElem);
+ }
- if (status->curEntry != NULL)
- {
- /* Continuing scan of curBucket... */
- HASHELEMENT *curElem;
-
- curElem = status->curEntry;
- status->curEntry = curElem->link;
- if (status->curEntry == NULL) /* end of this bucket */
- ++status->curBucket;
- return (void *) ELEMENTKEY(curElem);
- }
+ /*
+ * Search for next nonempty bucket starting at curBucket.
+ */
+ curBucket = status->curBucket;
+ hashp = status->hashp;
+ hctl = hashp->hctl;
+ ssize = hctl->ssize;
+ max_bucket = hctl->max_bucket;
- /*
- * initialize the search within this bucket.
- */
- segment_num = status->curBucket >> hctl->sshift;
- segment_ndx = MOD(status->curBucket, hctl->ssize);
+ if (curBucket > max_bucket)
+ return NULL; /* search is done */
- /*
- * first find the right segment in the table directory.
- */
- segp = hashp->dir[segment_num];
- if (segp == NULL)
- hash_corrupted(hashp);
+ /*
+ * first find the right segment in the table directory.
+ */
+ segment_num = curBucket >> hctl->sshift;
+ segment_ndx = MOD(curBucket, ssize);
- /*
- * now find the right index into the segment for the first item in
- * this bucket's chain. if the bucket is not empty (its entry in
- * the dir is valid), we know this must correspond to a valid
- * element and not a freed element because it came out of the
- * directory of valid stuff. if there are elements in the bucket
- * chains that point to the freelist we're in big trouble.
- */
- status->curEntry = segp[segment_ndx];
+ segp = hashp->dir[segment_num];
- if (status->curEntry == NULL) /* empty bucket */
- ++status->curBucket;
+ /*
+ * Pick up the first item in this bucket's chain. If chain is
+ * not empty we can go back around the outer loop to search it.
+ * Otherwise we have to advance to find the next nonempty bucket.
+ * We try to optimize that case since searching a near-empty
+ * hashtable has to iterate this loop a lot.
+ */
+ while ((curElem = segp[segment_ndx]) == NULL)
+ {
+ /* empty bucket, advance to next */
+ if (++curBucket > max_bucket)
+ {
+ status->curBucket = curBucket;
+ return NULL; /* search is done */
+ }
+ if (++segment_ndx >= ssize)
+ {
+ segment_num++;
+ segment_ndx = 0;
+ segp = hashp->dir[segment_num];
+ }
}
- return NULL; /* out of buckets */
+ /* Begin scan of curBucket... */
+ status->curEntry = curElem->link;
+ if (status->curEntry == NULL) /* end of this bucket */
+ ++curBucket;
+ status->curBucket = curBucket;
+ return (void *) ELEMENTKEY(curElem);
}
{
memcpy(p, old_p, old_dirsize);
MemSet(((char *) p) + old_dirsize, 0, new_dirsize - old_dirsize);
- MEM_FREE((char *) old_p);
hashp->dir = p;
hashp->hctl->dsize = new_dsize;
+
+ /* XXX assume the allocator is palloc, so we know how to free */
+ Assert(hashp->alloc == DynaHashAlloc);
+ pfree(old_p);
+
return true;
}
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