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/*
* simplehash.h
*
* Hash table implementation which will be specialized to user-defined
* types, by including this file to generate the required code. It's
* probably not worthwhile to do so for hash tables that aren't performance
* or space sensitive.
*
* Usage notes:
*
* To generate a hash-table and associated functions for a use case several
* macros have to be #define'ed before this file is included. Including
* the file #undef's all those, so a new hash table can be generated
* afterwards.
* The relevant parameters are:
* - SH_PREFIX - prefix for all symbol names generated. A prefix of 'foo'
* will result in hash table type 'foo_hash' and functions like
* 'foo_insert'/'foo_lookup' and so forth.
* - SH_ELEMENT_TYPE - type of the contained elements
* - SH_KEY_TYPE - type of the hashtable's key
* - SH_DECLARE - if defined function prototypes and type declarations are
* generated
* - SH_DEFINE - if defined function definitions are generated
* - SH_SCOPE - in which scope (e.g. extern, static inline) do function
* declarations reside
* - SH_USE_NONDEFAULT_ALLOCATOR - if defined no element allocator functions
* are defined, so you can supply your own
* The following parameters are only relevant when SH_DEFINE is defined:
* - SH_KEY - name of the element in SH_ELEMENT_TYPE containing the hash key
* - SH_EQUAL(table, a, b) - compare two table keys
* - SH_HASH_KEY(table, key) - generate hash for the key
* - SH_STORE_HASH - if defined the hash is stored in the elements
* - SH_GET_HASH(tb, a) - return the field to store the hash in
*
* For examples of usage look at simplehash.c (file local definition) and
* execnodes.h/execGrouping.c (exposed declaration, file local
* implementation).
*
* Hash table design:
*
* The hash table design chosen is a variant of linear open-addressing. The
* reason for doing so is that linear addressing is CPU cache & pipeline
* friendly. The biggest disadvantage of simple linear addressing schemes
* are highly variable lookup times due to clustering, and deletions
* leaving a lot of tombstones around. To address these issues a variant
* of "robin hood" hashing is employed. Robin hood hashing optimizes
* chaining lengths by moving elements close to their optimal bucket
* ("rich" elements), out of the way if a to-be-inserted element is further
* away from its optimal position (i.e. it's "poor"). While that can make
* insertions slower, the average lookup performance is a lot better, and
* higher fill factors can be used in a still performant manner. To avoid
* tombstones - which normally solve the issue that a deleted node's
* presence is relevant to determine whether a lookup needs to continue
* looking or is done - buckets following a deleted element are shifted
* backwards, unless they're empty or already at their optimal position.
*/
/* helpers */
#define SH_MAKE_PREFIX(a) CppConcat(a,_)
#define SH_MAKE_NAME(name) SH_MAKE_NAME_(SH_MAKE_PREFIX(SH_PREFIX),name)
#define SH_MAKE_NAME_(a,b) CppConcat(a,b)
/* name macros for: */
/* type declarations */
#define SH_TYPE SH_MAKE_NAME(hash)
#define SH_STATUS SH_MAKE_NAME(status)
#define SH_STATUS_EMPTY SH_MAKE_NAME(EMPTY)
#define SH_STATUS_IN_USE SH_MAKE_NAME(IN_USE)
#define SH_ITERATOR SH_MAKE_NAME(iterator)
/* function declarations */
#define SH_CREATE SH_MAKE_NAME(create)
#define SH_DESTROY SH_MAKE_NAME(destroy)
#define SH_RESET SH_MAKE_NAME(reset)
#define SH_INSERT SH_MAKE_NAME(insert)
#define SH_DELETE SH_MAKE_NAME(delete)
#define SH_LOOKUP SH_MAKE_NAME(lookup)
#define SH_GROW SH_MAKE_NAME(grow)
#define SH_START_ITERATE SH_MAKE_NAME(start_iterate)
#define SH_START_ITERATE_AT SH_MAKE_NAME(start_iterate_at)
#define SH_ITERATE SH_MAKE_NAME(iterate)
#define SH_ALLOCATE SH_MAKE_NAME(allocate)
#define SH_FREE SH_MAKE_NAME(free)
#define SH_STAT SH_MAKE_NAME(stat)
/* internal helper functions (no externally visible prototypes) */
#define SH_COMPUTE_PARAMETERS SH_MAKE_NAME(compute_parameters)
#define SH_NEXT SH_MAKE_NAME(next)
#define SH_PREV SH_MAKE_NAME(prev)
#define SH_DISTANCE_FROM_OPTIMAL SH_MAKE_NAME(distance)
#define SH_INITIAL_BUCKET SH_MAKE_NAME(initial_bucket)
#define SH_ENTRY_HASH SH_MAKE_NAME(entry_hash)
/* generate forward declarations necessary to use the hash table */
#ifdef SH_DECLARE
/* type definitions */
typedef struct SH_TYPE
{
/*
* Size of data / bucket array, 64 bits to handle UINT32_MAX sized hash
* tables. Note that the maximum number of elements is lower
* (SH_MAX_FILLFACTOR)
*/
uint64 size;
/* how many elements have valid contents */
uint32 members;
/* mask for bucket and size calculations, based on size */
uint32 sizemask;
/* boundary after which to grow hashtable */
uint32 grow_threshold;
/* hash buckets */
SH_ELEMENT_TYPE *data;
/* memory context to use for allocations */
MemoryContext ctx;
/* user defined data, useful for callbacks */
void *private_data;
} SH_TYPE;
typedef enum SH_STATUS
{
SH_STATUS_EMPTY = 0x00,
SH_STATUS_IN_USE = 0x01
} SH_STATUS;
typedef struct SH_ITERATOR
{
uint32 cur; /* current element */
uint32 end;
bool done; /* iterator exhausted? */
} SH_ITERATOR;
/* externally visible function prototypes */
SH_SCOPE SH_TYPE *SH_CREATE(MemoryContext ctx, uint32 nelements,
void *private_data);
SH_SCOPE void SH_DESTROY(SH_TYPE * tb);
SH_SCOPE void SH_RESET(SH_TYPE * tb);
SH_SCOPE void SH_GROW(SH_TYPE * tb, uint64 newsize);
SH_SCOPE SH_ELEMENT_TYPE *SH_INSERT(SH_TYPE * tb, SH_KEY_TYPE key, bool *found);
SH_SCOPE SH_ELEMENT_TYPE *SH_LOOKUP(SH_TYPE * tb, SH_KEY_TYPE key);
SH_SCOPE bool SH_DELETE(SH_TYPE * tb, SH_KEY_TYPE key);
SH_SCOPE void SH_START_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter);
SH_SCOPE void SH_START_ITERATE_AT(SH_TYPE * tb, SH_ITERATOR * iter, uint32 at);
SH_SCOPE SH_ELEMENT_TYPE *SH_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter);
SH_SCOPE void SH_STAT(SH_TYPE * tb);
#endif /* SH_DECLARE */
/* generate implementation of the hash table */
#ifdef SH_DEFINE
#include "utils/memutils.h"
/* max data array size,we allow up to PG_UINT32_MAX buckets, including 0 */
#define SH_MAX_SIZE (((uint64) PG_UINT32_MAX) + 1)
/* normal fillfactor, unless already close to maximum */
#ifndef SH_FILLFACTOR
#define SH_FILLFACTOR (0.9)
#endif
/* increase fillfactor if we otherwise would error out */
#define SH_MAX_FILLFACTOR (0.98)
/* grow if actual and optimal location bigger than */
#ifndef SH_GROW_MAX_DIB
#define SH_GROW_MAX_DIB 25
#endif
/* grow if more than elements to move when inserting */
#ifndef SH_GROW_MAX_MOVE
#define SH_GROW_MAX_MOVE 150
#endif
#ifndef SH_GROW_MIN_FILLFACTOR
/* but do not grow due to SH_GROW_MAX_* if below */
#define SH_GROW_MIN_FILLFACTOR 0.1
#endif
#ifdef SH_STORE_HASH
#define SH_COMPARE_KEYS(tb, ahash, akey, b) (ahash == SH_GET_HASH(tb, b) && SH_EQUAL(tb, b->SH_KEY, akey))
#else
#define SH_COMPARE_KEYS(tb, ahash, akey, b) (SH_EQUAL(tb, b->SH_KEY, akey))
#endif
/* FIXME: can we move these to a central location? */
/* calculate ceil(log base 2) of num */
static inline uint64
sh_log2(uint64 num)
{
int i;
uint64 limit;
for (i = 0, limit = 1; limit < num; i++, limit <<= 1)
;
return i;
}
/* calculate first power of 2 >= num */
static inline uint64
sh_pow2(uint64 num)
{
return ((uint64) 1) << sh_log2(num);
}
/*
* Compute sizing parameters for hashtable. Called when creating and growing
* the hashtable.
*/
static inline void
SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint64 newsize)
{
uint64 size;
/* supporting zero sized hashes would complicate matters */
size = Max(newsize, 2);
/* round up size to the next power of 2, that's how bucketing works */
size = sh_pow2(size);
Assert(size <= SH_MAX_SIZE);
/*
* Verify that allocation of ->data is possible on this platform, without
* overflowing Size.
*/
if ((((uint64) sizeof(SH_ELEMENT_TYPE)) * size) >= MaxAllocHugeSize)
elog(ERROR, "hash table too large");
/* now set size */
tb->size = size;
tb->sizemask = (uint32) (size - 1);
/*
* Compute the next threshold at which we need to grow the hash table
* again.
*/
if (tb->size == SH_MAX_SIZE)
tb->grow_threshold = ((double) tb->size) * SH_MAX_FILLFACTOR;
else
tb->grow_threshold = ((double) tb->size) * SH_FILLFACTOR;
}
/* return the optimal bucket for the hash */
static inline uint32
SH_INITIAL_BUCKET(SH_TYPE * tb, uint32 hash)
{
return hash & tb->sizemask;
}
/* return next bucket after the current, handling wraparound */
static inline uint32
SH_NEXT(SH_TYPE * tb, uint32 curelem, uint32 startelem)
{
curelem = (curelem + 1) & tb->sizemask;
Assert(curelem != startelem);
return curelem;
}
/* return bucket before the current, handling wraparound */
static inline uint32
SH_PREV(SH_TYPE * tb, uint32 curelem, uint32 startelem)
{
curelem = (curelem - 1) & tb->sizemask;
Assert(curelem != startelem);
return curelem;
}
/* return distance between bucket and its optimal position */
static inline uint32
SH_DISTANCE_FROM_OPTIMAL(SH_TYPE * tb, uint32 optimal, uint32 bucket)
{
if (optimal <= bucket)
return bucket - optimal;
else
return (tb->size + bucket) - optimal;
}
static inline uint32
SH_ENTRY_HASH(SH_TYPE * tb, SH_ELEMENT_TYPE * entry)
{
#ifdef SH_STORE_HASH
return SH_GET_HASH(tb, entry);
#else
return SH_HASH_KEY(tb, entry->SH_KEY);
#endif
}
/* default memory allocator function */
static inline void *SH_ALLOCATE(SH_TYPE * type, Size size);
static inline void SH_FREE(SH_TYPE * type, void *pointer);
#ifndef SH_USE_NONDEFAULT_ALLOCATOR
/* default memory allocator function */
static inline void *
SH_ALLOCATE(SH_TYPE * type, Size size)
{
return MemoryContextAllocExtended(type->ctx, size,
MCXT_ALLOC_HUGE | MCXT_ALLOC_ZERO);
}
/* default memory free function */
static inline void
SH_FREE(SH_TYPE * type, void *pointer)
{
pfree(pointer);
}
#endif
/*
* Create a hash table with enough space for `nelements` distinct members.
* Memory for the hash table is allocated from the passed-in context. If
* desired, the array of elements can be allocated using a passed-in allocator;
* this could be useful in order to place the array of elements in a shared
* memory, or in a context that will outlive the rest of the hash table.
* Memory other than for the array of elements will still be allocated from
* the passed-in context.
*/
SH_SCOPE SH_TYPE *
SH_CREATE(MemoryContext ctx, uint32 nelements, void *private_data)
{
SH_TYPE *tb;
uint64 size;
tb = MemoryContextAllocZero(ctx, sizeof(SH_TYPE));
tb->ctx = ctx;
tb->private_data = private_data;
/* increase nelements by fillfactor, want to store nelements elements */
size = Min((double) SH_MAX_SIZE, ((double) nelements) / SH_FILLFACTOR);
SH_COMPUTE_PARAMETERS(tb, size);
tb->data = SH_ALLOCATE(tb, sizeof(SH_ELEMENT_TYPE) * tb->size);
return tb;
}
/* destroy a previously created hash table */
SH_SCOPE void
SH_DESTROY(SH_TYPE * tb)
{
SH_FREE(tb, tb->data);
pfree(tb);
}
/* reset the contents of a previously created hash table */
SH_SCOPE void
SH_RESET(SH_TYPE * tb)
{
memset(tb->data, 0, sizeof(SH_ELEMENT_TYPE) * tb->size);
tb->members = 0;
}
/*
* Grow a hash table to at least `newsize` buckets.
*
* Usually this will automatically be called by insertions/deletions, when
* necessary. But resizing to the exact input size can be advantageous
* performance-wise, when known at some point.
*/
SH_SCOPE void
SH_GROW(SH_TYPE * tb, uint64 newsize)
{
uint64 oldsize = tb->size;
SH_ELEMENT_TYPE *olddata = tb->data;
SH_ELEMENT_TYPE *newdata;
uint32 i;
uint32 startelem = 0;
uint32 copyelem;
Assert(oldsize == sh_pow2(oldsize));
Assert(oldsize != SH_MAX_SIZE);
Assert(oldsize < newsize);
/* compute parameters for new table */
SH_COMPUTE_PARAMETERS(tb, newsize);
tb->data = SH_ALLOCATE(tb, sizeof(SH_ELEMENT_TYPE) * tb->size);
newdata = tb->data;
/*
* Copy entries from the old data to newdata. We theoretically could use
* SH_INSERT here, to avoid code duplication, but that's more general than
* we need. We neither want tb->members increased, nor do we need to do
* deal with deleted elements, nor do we need to compare keys. So a
* special-cased implementation is lot faster. As resizing can be time
* consuming and frequent, that's worthwhile to optimize.
*
* To be able to simply move entries over, we have to start not at the
* first bucket (i.e olddata[0]), but find the first bucket that's either
* empty, or is occupied by an entry at its optimal position. Such a
* bucket has to exist in any table with a load factor under 1, as not all
* buckets are occupied, i.e. there always has to be an empty bucket. By
* starting at such a bucket we can move the entries to the larger table,
* without having to deal with conflicts.
*/
/* search for the first element in the hash that's not wrapped around */
for (i = 0; i < oldsize; i++)
{
SH_ELEMENT_TYPE *oldentry = &olddata[i];
uint32 hash;
uint32 optimal;
if (oldentry->status != SH_STATUS_IN_USE)
{
startelem = i;
break;
}
hash = SH_ENTRY_HASH(tb, oldentry);
optimal = SH_INITIAL_BUCKET(tb, hash);
if (optimal == i)
{
startelem = i;
break;
}
}
/* and copy all elements in the old table */
copyelem = startelem;
for (i = 0; i < oldsize; i++)
{
SH_ELEMENT_TYPE *oldentry = &olddata[copyelem];
if (oldentry->status == SH_STATUS_IN_USE)
{
uint32 hash;
uint32 startelem;
uint32 curelem;
SH_ELEMENT_TYPE *newentry;
hash = SH_ENTRY_HASH(tb, oldentry);
startelem = SH_INITIAL_BUCKET(tb, hash);
curelem = startelem;
/* find empty element to put data into */
while (true)
{
newentry = &newdata[curelem];
if (newentry->status == SH_STATUS_EMPTY)
{
break;
}
curelem = SH_NEXT(tb, curelem, startelem);
}
/* copy entry to new slot */
memcpy(newentry, oldentry, sizeof(SH_ELEMENT_TYPE));
}
/* can't use SH_NEXT here, would use new size */
copyelem++;
if (copyelem >= oldsize)
{
copyelem = 0;
}
}
SH_FREE(tb, olddata);
}
/*
* Insert the key key into the hash-table, set *found to true if the key
* already exists, false otherwise. Returns the hash-table entry in either
* case.
*/
SH_SCOPE SH_ELEMENT_TYPE *
SH_INSERT(SH_TYPE * tb, SH_KEY_TYPE key, bool *found)
{
uint32 hash = SH_HASH_KEY(tb, key);
uint32 startelem;
uint32 curelem;
SH_ELEMENT_TYPE *data;
uint32 insertdist;
restart:
insertdist = 0;
/*
* We do the grow check even if the key is actually present, to avoid
* doing the check inside the loop. This also lets us avoid having to
* re-find our position in the hashtable after resizing.
*
* Note that this also reached when resizing the table due to
* SH_GROW_MAX_DIB / SH_GROW_MAX_MOVE.
*/
if (unlikely(tb->members >= tb->grow_threshold))
{
if (tb->size == SH_MAX_SIZE)
{
elog(ERROR, "hash table size exceeded");
}
/*
* When optimizing, it can be very useful to print these out.
*/
/* SH_STAT(tb); */
SH_GROW(tb, tb->size * 2);
/* SH_STAT(tb); */
}
/* perform insert, start bucket search at optimal location */
data = tb->data;
startelem = SH_INITIAL_BUCKET(tb, hash);
curelem = startelem;
while (true)
{
uint32 curdist;
uint32 curhash;
uint32 curoptimal;
SH_ELEMENT_TYPE *entry = &data[curelem];
/* any empty bucket can directly be used */
if (entry->status == SH_STATUS_EMPTY)
{
tb->members++;
entry->SH_KEY = key;
#ifdef SH_STORE_HASH
SH_GET_HASH(tb, entry) = hash;
#endif
entry->status = SH_STATUS_IN_USE;
*found = false;
return entry;
}
/*
* If the bucket is not empty, we either found a match (in which case
* we're done), or we have to decide whether to skip over or move the
* colliding entry. When the colliding element's distance to its
* optimal position is smaller than the to-be-inserted entry's, we
* shift the colliding entry (and its followers) forward by one.
*/
if (SH_COMPARE_KEYS(tb, hash, key, entry))
{
Assert(entry->status == SH_STATUS_IN_USE);
*found = true;
return entry;
}
curhash = SH_ENTRY_HASH(tb, entry);
curoptimal = SH_INITIAL_BUCKET(tb, curhash);
curdist = SH_DISTANCE_FROM_OPTIMAL(tb, curoptimal, curelem);
if (insertdist > curdist)
{
SH_ELEMENT_TYPE *lastentry = entry;
uint32 emptyelem = curelem;
uint32 moveelem;
int32 emptydist = 0;
/* find next empty bucket */
while (true)
{
SH_ELEMENT_TYPE *emptyentry;
emptyelem = SH_NEXT(tb, emptyelem, startelem);
emptyentry = &data[emptyelem];
if (emptyentry->status == SH_STATUS_EMPTY)
{
lastentry = emptyentry;
break;
}
/*
* To avoid negative consequences from overly imbalanced
* hashtables, grow the hashtable if collisions would require
* us to move a lot of entries. The most likely cause of such
* imbalance is filling a (currently) small table, from a
* currently big one, in hash-table order. Don't grow if the
* hashtable would be too empty, to prevent quick space
* explosion for some weird edge cases.
*/
if (unlikely(++emptydist > SH_GROW_MAX_MOVE) &&
((double) tb->members / tb->size) >= SH_GROW_MIN_FILLFACTOR)
{
tb->grow_threshold = 0;
goto restart;
}
}
/* shift forward, starting at last occupied element */
/*
* TODO: This could be optimized to be one memcpy in may cases,
* excepting wrapping around at the end of ->data. Hasn't shown up
* in profiles so far though.
*/
moveelem = emptyelem;
while (moveelem != curelem)
{
SH_ELEMENT_TYPE *moveentry;
moveelem = SH_PREV(tb, moveelem, startelem);
moveentry = &data[moveelem];
memcpy(lastentry, moveentry, sizeof(SH_ELEMENT_TYPE));
lastentry = moveentry;
}
/* and fill the now empty spot */
tb->members++;
entry->SH_KEY = key;
#ifdef SH_STORE_HASH
SH_GET_HASH(tb, entry) = hash;
#endif
entry->status = SH_STATUS_IN_USE;
*found = false;
return entry;
}
curelem = SH_NEXT(tb, curelem, startelem);
insertdist++;
/*
* To avoid negative consequences from overly imbalanced hashtables,
* grow the hashtable if collisions lead to large runs. The most
* likely cause of such imbalance is filling a (currently) small
* table, from a currently big one, in hash-table order. Don't grow
* if the hashtable would be too empty, to prevent quick space
* explosion for some weird edge cases.
*/
if (unlikely(insertdist > SH_GROW_MAX_DIB) &&
((double) tb->members / tb->size) >= SH_GROW_MIN_FILLFACTOR)
{
tb->grow_threshold = 0;
goto restart;
}
}
}
/*
* Lookup up entry in hash table. Returns NULL if key not present.
*/
SH_SCOPE SH_ELEMENT_TYPE *
SH_LOOKUP(SH_TYPE * tb, SH_KEY_TYPE key)
{
uint32 hash = SH_HASH_KEY(tb, key);
const uint32 startelem = SH_INITIAL_BUCKET(tb, hash);
uint32 curelem = startelem;
while (true)
{
SH_ELEMENT_TYPE *entry = &tb->data[curelem];
if (entry->status == SH_STATUS_EMPTY)
{
return NULL;
}
Assert(entry->status == SH_STATUS_IN_USE);
if (SH_COMPARE_KEYS(tb, hash, key, entry))
return entry;
/*
* TODO: we could stop search based on distance. If the current
* buckets's distance-from-optimal is smaller than what we've skipped
* already, the entry doesn't exist. Probably only do so if
* SH_STORE_HASH is defined, to avoid re-computing hashes?
*/
curelem = SH_NEXT(tb, curelem, startelem);
}
}
/*
* Delete entry from hash table. Returns whether to-be-deleted key was
* present.
*/
SH_SCOPE bool
SH_DELETE(SH_TYPE * tb, SH_KEY_TYPE key)
{
uint32 hash = SH_HASH_KEY(tb, key);
uint32 startelem = SH_INITIAL_BUCKET(tb, hash);
uint32 curelem = startelem;
while (true)
{
SH_ELEMENT_TYPE *entry = &tb->data[curelem];
if (entry->status == SH_STATUS_EMPTY)
return false;
if (entry->status == SH_STATUS_IN_USE &&
SH_COMPARE_KEYS(tb, hash, key, entry))
{
SH_ELEMENT_TYPE *lastentry = entry;
tb->members--;
/*
* Backward shift following elements till either an empty element
* or an element at its optimal position is encountered.
*
* While that sounds expensive, the average chain length is short,
* and deletions would otherwise require tombstones.
*/
while (true)
{
SH_ELEMENT_TYPE *curentry;
uint32 curhash;
uint32 curoptimal;
curelem = SH_NEXT(tb, curelem, startelem);
curentry = &tb->data[curelem];
if (curentry->status != SH_STATUS_IN_USE)
{
lastentry->status = SH_STATUS_EMPTY;
break;
}
curhash = SH_ENTRY_HASH(tb, curentry);
curoptimal = SH_INITIAL_BUCKET(tb, curhash);
/* current is at optimal position, done */
if (curoptimal == curelem)
{
lastentry->status = SH_STATUS_EMPTY;
break;
}
/* shift */
memcpy(lastentry, curentry, sizeof(SH_ELEMENT_TYPE));
lastentry = curentry;
}
return true;
}
/* TODO: return false; if distance too big */
curelem = SH_NEXT(tb, curelem, startelem);
}
}
/*
* Initialize iterator.
*/
SH_SCOPE void
SH_START_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter)
{
uint32 i;
uint64 startelem = PG_UINT64_MAX;
/*
* Search for the first empty element. As deletions during iterations are
* supported, we want to start/end at an element that cannot be affected
* by elements being shifted.
*/
for (i = 0; i < tb->size; i++)
{
SH_ELEMENT_TYPE *entry = &tb->data[i];
if (entry->status != SH_STATUS_IN_USE)
{
startelem = i;
break;
}
}
/* we should have found an empty element */
Assert(startelem < SH_MAX_SIZE);
/*
* Iterate backwards, that allows the current element to be deleted, even
* if there are backward shifts
*/
iter->cur = startelem;
iter->end = iter->cur;
iter->done = false;
}
/*
* Initialize iterator to a specific bucket. That's really only useful for
* cases where callers are partially iterating over the hashspace, and that
* iteration deletes and inserts elements based on visited entries. Doing that
* repeatedly could lead to an unbalanced keyspace when always starting at the
* same position.
*/
SH_SCOPE void
SH_START_ITERATE_AT(SH_TYPE * tb, SH_ITERATOR * iter, uint32 at)
{
/*
* Iterate backwards, that allows the current element to be deleted, even
* if there are backward shifts.
*/
iter->cur = at & tb->sizemask; /* ensure at is within a valid range */
iter->end = iter->cur;
iter->done = false;
}
/*
* Iterate over all entries in the hash-table. Return the next occupied entry,
* or NULL if done.
*
* During iteration the current entry in the hash table may be deleted,
* without leading to elements being skipped or returned twice. Additionally
* the rest of the table may be modified (i.e. there can be insertions or
* deletions), but if so, there's neither a guarantee that all nodes are
* visited at least once, nor a guarantee that a node is visited at most once.
*/
SH_SCOPE SH_ELEMENT_TYPE *
SH_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter)
{
while (!iter->done)
{
SH_ELEMENT_TYPE *elem;
elem = &tb->data[iter->cur];
/* next element in backward direction */
iter->cur = (iter->cur - 1) & tb->sizemask;
if ((iter->cur & tb->sizemask) == (iter->end & tb->sizemask))
iter->done = true;
if (elem->status == SH_STATUS_IN_USE)
{
return elem;
}
}
return NULL;
}
/*
* Report some statistics about the state of the hashtable. For
* debugging/profiling purposes only.
*/
SH_SCOPE void
SH_STAT(SH_TYPE * tb)
{
uint32 max_chain_length = 0;
uint32 total_chain_length = 0;
double avg_chain_length;
double fillfactor;
uint32 i;
uint32 *collisions = palloc0(tb->size * sizeof(uint32));
uint32 total_collisions = 0;
uint32 max_collisions = 0;
double avg_collisions;
for (i = 0; i < tb->size; i++)
{
uint32 hash;
uint32 optimal;
uint32 dist;
SH_ELEMENT_TYPE *elem;
elem = &tb->data[i];
if (elem->status != SH_STATUS_IN_USE)
continue;
hash = SH_ENTRY_HASH(tb, elem);
optimal = SH_INITIAL_BUCKET(tb, hash);
dist = SH_DISTANCE_FROM_OPTIMAL(tb, optimal, i);
if (dist > max_chain_length)
max_chain_length = dist;
total_chain_length += dist;
collisions[optimal]++;
}
for (i = 0; i < tb->size; i++)
{
uint32 curcoll = collisions[i];
if (curcoll == 0)
continue;
/* single contained element is not a collision */
curcoll--;
total_collisions += curcoll;
if (curcoll > max_collisions)
max_collisions = curcoll;
}
if (tb->members > 0)
{
fillfactor = tb->members / ((double) tb->size);
avg_chain_length = ((double) total_chain_length) / tb->members;
avg_collisions = ((double) total_collisions) / tb->members;
}
else
{
fillfactor = 0;
avg_chain_length = 0;
avg_collisions = 0;
}
elog(LOG, "size: " UINT64_FORMAT ", members: %u, filled: %f, total chain: %u, max chain: %u, avg chain: %f, total_collisions: %u, max_collisions: %i, avg_collisions: %f",
tb->size, tb->members, fillfactor, total_chain_length, max_chain_length, avg_chain_length,
total_collisions, max_collisions, avg_collisions);
}
#endif /* SH_DEFINE */
/* undefine external parameters, so next hash table can be defined */
#undef SH_PREFIX
#undef SH_KEY_TYPE
#undef SH_KEY
#undef SH_ELEMENT_TYPE
#undef SH_HASH_KEY
#undef SH_SCOPE
#undef SH_DECLARE
#undef SH_DEFINE
#undef SH_GET_HASH
#undef SH_STORE_HASH
#undef SH_USE_NONDEFAULT_ALLOCATOR
/* undefine locally declared macros */
#undef SH_MAKE_PREFIX
#undef SH_MAKE_NAME
#undef SH_MAKE_NAME_
#undef SH_FILLFACTOR
#undef SH_MAX_FILLFACTOR
#undef SH_GROW_MAX_DIB
#undef SH_GROW_MAX_MOVE
#undef SH_GROW_MIN_FILLFACTOR
#undef SH_MAX_SIZE
/* types */
#undef SH_TYPE
#undef SH_STATUS
#undef SH_STATUS_EMPTY
#undef SH_STATUS_IN_USE
#undef SH_ITERATOR
/* external function names */
#undef SH_CREATE
#undef SH_DESTROY
#undef SH_RESET
#undef SH_INSERT
#undef SH_DELETE
#undef SH_LOOKUP
#undef SH_GROW
#undef SH_START_ITERATE
#undef SH_START_ITERATE_AT
#undef SH_ITERATE
#undef SH_ALLOCATE
#undef SH_FREE
#undef SH_STAT
/* internal function names */
#undef SH_COMPUTE_PARAMETERS
#undef SH_COMPARE_KEYS
#undef SH_INITIAL_BUCKET
#undef SH_NEXT
#undef SH_PREV
#undef SH_DISTANCE_FROM_OPTIMAL
#undef SH_ENTRY_HASH
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