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Diffstat (limited to 'src/include/lib/simplehash.h')
| -rw-r--r-- | src/include/lib/simplehash.h | 1059 |
1 files changed, 1059 insertions, 0 deletions
diff --git a/src/include/lib/simplehash.h b/src/include/lib/simplehash.h new file mode 100644 index 0000000..90dfa8a --- /dev/null +++ b/src/include/lib/simplehash.h @@ -0,0 +1,1059 @@ +/* + * 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_RAW_ALLOCATOR - if defined, memory contexts are not used; instead, + * use this to allocate bytes + * - 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 tidbitmap.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. + */ + +#include "port/pg_bitutils.h" + +/* 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(SH_EMPTY) +#define SH_STATUS_IN_USE SH_MAKE_NAME(SH_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_INSERT_HASH SH_MAKE_NAME(insert_hash) +#define SH_DELETE SH_MAKE_NAME(delete) +#define SH_LOOKUP SH_MAKE_NAME(lookup) +#define SH_LOOKUP_HASH SH_MAKE_NAME(lookup_hash) +#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) +#define SH_INSERT_HASH_INTERNAL SH_MAKE_NAME(insert_hash_internal) +#define SH_LOOKUP_HASH_INTERNAL SH_MAKE_NAME(lookup_hash_internal) + +/* 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; + +#ifndef SH_RAW_ALLOCATOR + /* memory context to use for allocations */ + MemoryContext ctx; +#endif + + /* 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 */ +#ifdef SH_RAW_ALLOCATOR +SH_SCOPE SH_TYPE *SH_CREATE(uint32 nelements, void *private_data); +#else +SH_SCOPE SH_TYPE *SH_CREATE(MemoryContext ctx, uint32 nelements, + void *private_data); +#endif +SH_SCOPE void SH_DESTROY(SH_TYPE * tb); +SH_SCOPE void SH_RESET(SH_TYPE * tb); +SH_SCOPE void SH_GROW(SH_TYPE * tb, uint32 newsize); +SH_SCOPE SH_ELEMENT_TYPE *SH_INSERT(SH_TYPE * tb, SH_KEY_TYPE key, bool *found); +SH_SCOPE SH_ELEMENT_TYPE *SH_INSERT_HASH(SH_TYPE * tb, SH_KEY_TYPE key, + uint32 hash, bool *found); +SH_SCOPE SH_ELEMENT_TYPE *SH_LOOKUP(SH_TYPE * tb, SH_KEY_TYPE key); +SH_SCOPE SH_ELEMENT_TYPE *SH_LOOKUP_HASH(SH_TYPE * tb, SH_KEY_TYPE key, + uint32 hash); +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 + +#ifndef SH_RAW_ALLOCATOR +#include "utils/memutils.h" +#endif + +/* 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 + +/* + * Wrap the following definitions in include guards, to avoid multiple + * definition errors if this header is included more than once. The rest of + * the file deliberately has no include guards, because it can be included + * with different parameters to define functions and types with non-colliding + * names. + */ +#ifndef SIMPLEHASH_H +#define SIMPLEHASH_H + +#ifdef FRONTEND +#define sh_error(...) pg_log_error(__VA_ARGS__) +#define sh_log(...) pg_log_info(__VA_ARGS__) +#else +#define sh_error(...) elog(ERROR, __VA_ARGS__) +#define sh_log(...) elog(LOG, __VA_ARGS__) +#endif + +#endif + +/* + * Compute sizing parameters for hashtable. Called when creating and growing + * the hashtable. + */ +static inline void +SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint32 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 = pg_nextpower2_64(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) >= SIZE_MAX / 2) + sh_error("hash table too large"); + + /* now set size */ + tb->size = size; + + if (tb->size == SH_MAX_SIZE) + tb->sizemask = 0; + else + tb->sizemask = tb->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) +{ +#ifdef SH_RAW_ALLOCATOR + return SH_RAW_ALLOCATOR(size); +#else + return MemoryContextAllocExtended(type->ctx, size, + MCXT_ALLOC_HUGE | MCXT_ALLOC_ZERO); +#endif +} + +/* 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. + */ +#ifdef SH_RAW_ALLOCATOR +SH_SCOPE SH_TYPE * +SH_CREATE(uint32 nelements, void *private_data) +#else +SH_SCOPE SH_TYPE * +SH_CREATE(MemoryContext ctx, uint32 nelements, void *private_data) +#endif +{ + SH_TYPE *tb; + uint64 size; + +#ifdef SH_RAW_ALLOCATOR + tb = SH_RAW_ALLOCATOR(sizeof(SH_TYPE)); +#else + tb = MemoryContextAllocZero(ctx, sizeof(SH_TYPE)); + tb->ctx = ctx; +#endif + 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, uint32 newsize) +{ + uint64 oldsize = tb->size; + SH_ELEMENT_TYPE *olddata = tb->data; + SH_ELEMENT_TYPE *newdata; + uint32 i; + uint32 startelem = 0; + uint32 copyelem; + + Assert(oldsize == pg_nextpower2_64(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); +} + +/* + * This is a separate static inline function, so it can be reliably be inlined + * into its wrapper functions even if SH_SCOPE is extern. + */ +static inline SH_ELEMENT_TYPE * +SH_INSERT_HASH_INTERNAL(SH_TYPE * tb, SH_KEY_TYPE key, uint32 hash, bool *found) +{ + 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) + { + sh_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 many 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; + } + } +} + +/* + * 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); + + return SH_INSERT_HASH_INTERNAL(tb, key, hash, found); +} + +/* + * Insert the key key into the hash-table using an already-calculated + * hash. 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_HASH(SH_TYPE * tb, SH_KEY_TYPE key, uint32 hash, bool *found) +{ + return SH_INSERT_HASH_INTERNAL(tb, key, hash, found); +} + +/* + * This is a separate static inline function, so it can be reliably be inlined + * into its wrapper functions even if SH_SCOPE is extern. + */ +static inline SH_ELEMENT_TYPE * +SH_LOOKUP_HASH_INTERNAL(SH_TYPE * tb, SH_KEY_TYPE key, uint32 hash) +{ + 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); + } +} + +/* + * 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); + + return SH_LOOKUP_HASH_INTERNAL(tb, key, hash); +} + +/* + * Lookup up entry in hash table using an already-calculated hash. + * + * Returns NULL if key not present. + */ +SH_SCOPE SH_ELEMENT_TYPE * +SH_LOOKUP_HASH(SH_TYPE * tb, SH_KEY_TYPE key, uint32 hash) +{ + return SH_LOOKUP_HASH_INTERNAL(tb, key, hash); +} + +/* + * 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) +{ + int 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; + } + } + + 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; + } + + sh_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 +#undef SH_EQUAL + +/* 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_INSERT_HASH +#undef SH_DELETE +#undef SH_LOOKUP +#undef SH_LOOKUP_HASH +#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 +#undef SH_INSERT_HASH_INTERNAL +#undef SH_LOOKUP_HASH_INTERNAL |