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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:15:05 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:15:05 +0000
commit46651ce6fe013220ed397add242004d764fc0153 (patch)
tree6e5299f990f88e60174a1d3ae6e48eedd2688b2b /src/include/lib/simplehash.h
parentInitial commit. (diff)
downloadpostgresql-14-46651ce6fe013220ed397add242004d764fc0153.tar.xz
postgresql-14-46651ce6fe013220ed397add242004d764fc0153.zip
Adding upstream version 14.5.upstream/14.5upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/include/lib/simplehash.h')
-rw-r--r--src/include/lib/simplehash.h1185
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diff --git a/src/include/lib/simplehash.h b/src/include/lib/simplehash.h
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+/*
+ * simplehash.h
+ *
+ * When included this file generates a "templated" (by way of macros)
+ * open-addressing hash table implementation specialized to user-defined
+ * types.
+ *
+ * It's probably not worthwhile to generate such a specialized implementation
+ * for hash tables that aren't performance or space sensitive.
+ *
+ * Compared to dynahash, simplehash has the following benefits:
+ *
+ * - Due to the "templated" code generation has known structure sizes and no
+ * indirect function calls (which show up substantially in dynahash
+ * profiles). These features considerably increase speed for small
+ * entries.
+ * - Open addressing has better CPU cache behavior than dynahash's chained
+ * hashtables.
+ * - The generated interface is type-safe and easier to use than dynahash,
+ * though at the cost of more complex setup.
+ * - Allocates memory in a MemoryContext or another allocator with a
+ * malloc/free style interface (which isn't easily usable in a shared
+ * memory context)
+ * - Does not require the overhead of a separate memory context.
+ *
+ * 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
+ *
+ * The element type is required to contain a "status" member that can store
+ * the range of values defined in the SH_STATUS enum.
+ *
+ * While SH_STORE_HASH (and subsequently SH_GET_HASH) are optional, because
+ * the hash table implementation needs to compare hashes to move elements
+ * (particularly when growing the hash), it's preferable, if possible, to
+ * store the element's hash in the element's data type. If the hash is so
+ * stored, the hash table will also compare hashes before calling SH_EQUAL
+ * when comparing two keys.
+ *
+ * For convenience the hash table create functions accept a void pointer
+ * that will be stored in the hash table type's member private_data. This
+ * allows callbacks to reference caller provided data.
+ *
+ * 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.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/lib/simplehash.h
+ */
+
+#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_ITEM SH_MAKE_NAME(delete_item)
+#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
+/* <prefix>_hash <prefix>_create(uint32 nelements, void *private_data) */
+SH_SCOPE SH_TYPE *SH_CREATE(uint32 nelements, void *private_data);
+#else
+/*
+ * <prefix>_hash <prefix>_create(MemoryContext ctx, uint32 nelements,
+ * void *private_data)
+ */
+SH_SCOPE SH_TYPE *SH_CREATE(MemoryContext ctx, uint32 nelements,
+ void *private_data);
+#endif
+
+/* void <prefix>_destroy(<prefix>_hash *tb) */
+SH_SCOPE void SH_DESTROY(SH_TYPE * tb);
+
+/* void <prefix>_reset(<prefix>_hash *tb) */
+SH_SCOPE void SH_RESET(SH_TYPE * tb);
+
+/* void <prefix>_grow(<prefix>_hash *tb, uint64 newsize) */
+SH_SCOPE void SH_GROW(SH_TYPE * tb, uint64 newsize);
+
+/* <element> *<prefix>_insert(<prefix>_hash *tb, <key> key, bool *found) */
+SH_SCOPE SH_ELEMENT_TYPE *SH_INSERT(SH_TYPE * tb, SH_KEY_TYPE key, bool *found);
+
+/*
+ * <element> *<prefix>_insert_hash(<prefix>_hash *tb, <key> key, uint32 hash,
+ * bool *found)
+ */
+SH_SCOPE SH_ELEMENT_TYPE *SH_INSERT_HASH(SH_TYPE * tb, SH_KEY_TYPE key,
+ uint32 hash, bool *found);
+
+/* <element> *<prefix>_lookup(<prefix>_hash *tb, <key> key) */
+SH_SCOPE SH_ELEMENT_TYPE *SH_LOOKUP(SH_TYPE * tb, SH_KEY_TYPE key);
+
+/* <element> *<prefix>_lookup_hash(<prefix>_hash *tb, <key> key, uint32 hash) */
+SH_SCOPE SH_ELEMENT_TYPE *SH_LOOKUP_HASH(SH_TYPE * tb, SH_KEY_TYPE key,
+ uint32 hash);
+
+/* void <prefix>_delete_item(<prefix>_hash *tb, <element> *entry) */
+SH_SCOPE void SH_DELETE_ITEM(SH_TYPE * tb, SH_ELEMENT_TYPE * entry);
+
+/* bool <prefix>_delete(<prefix>_hash *tb, <key> key) */
+SH_SCOPE bool SH_DELETE(SH_TYPE * tb, SH_KEY_TYPE key);
+
+/* void <prefix>_start_iterate(<prefix>_hash *tb, <prefix>_iterator *iter) */
+SH_SCOPE void SH_START_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter);
+
+/*
+ * void <prefix>_start_iterate_at(<prefix>_hash *tb, <prefix>_iterator *iter,
+ * uint32 at)
+ */
+SH_SCOPE void SH_START_ITERATE_AT(SH_TYPE * tb, SH_ITERATOR * iter, uint32 at);
+
+/* <element> *<prefix>_iterate(<prefix>_hash *tb, <prefix>_iterator *iter) */
+SH_SCOPE SH_ELEMENT_TYPE *SH_ITERATE(SH_TYPE * tb, SH_ITERATOR * iter);
+
+/* void <prefix>_stat(<prefix>_hash *tb */
+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(...) \
+ do { pg_log_fatal(__VA_ARGS__); exit(1); } while(0)
+#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, 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 = pg_nextpower2_64(size);
+ Assert(size <= SH_MAX_SIZE);
+
+ /*
+ * Verify that allocation of ->data is possible on this platform, without
+ * overflowing Size.
+ */
+ if (unlikely((((uint64) sizeof(SH_ELEMENT_TYPE)) * size) >= SIZE_MAX / 2))
+ sh_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)
+{
+#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, 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 == 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 (unlikely(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 by key. 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);
+ }
+}
+
+/*
+ * Delete entry from hash table by entry pointer
+ */
+SH_SCOPE void
+SH_DELETE_ITEM(SH_TYPE * tb, SH_ELEMENT_TYPE * entry)
+{
+ SH_ELEMENT_TYPE *lastentry = entry;
+ uint32 hash = SH_ENTRY_HASH(tb, entry);
+ uint32 startelem = SH_INITIAL_BUCKET(tb, hash);
+ uint32 curelem;
+
+ /* Calculate the index of 'entry' */
+ curelem = entry - &tb->data[0];
+
+ 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;
+ }
+}
+
+/*
+ * 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_ITEM
+#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