Adding upstream version 16.2.upstream/16.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1184 insertions, 0 deletions

diff --git a/src/include/lib/simplehash.h b/src/include/lib/simplehash.h
new file mode 100644
index 0000000..b7adc16
--- /dev/null
+++ b/src/include/lib/simplehash.h
@@ -0,0 +1,1184 @@
+/*
+ * 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. The allocator must zero the returned space.
+ *	  - 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) 1996-2023, 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(...) pg_fatal(__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, 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_TYPE *) SH_RAW_ALLOCATOR(sizeof(SH_TYPE));
+#else
+	tb = (SH_TYPE *) 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_ELEMENT_TYPE *) 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_ELEMENT_TYPE *) 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		startelem2;
+			uint32		curelem;
+			SH_ELEMENT_TYPE *newentry;
+
+			hash = SH_ENTRY_HASH(tb, oldentry);
+			startelem2 = SH_INITIAL_BUCKET(tb, hash);
+			curelem = startelem2;
+
+			/* find empty element to put data into */
+			while (true)
+			{
+				newentry = &newdata[curelem];
+
+				if (newentry->status == SH_STATUS_EMPTY)
+				{
+					break;
+				}
+
+				curelem = SH_NEXT(tb, curelem, startelem2);
+			}
+
+			/* 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 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 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)
+{
+	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 (uint32 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 = (uint32 *) 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: %u, 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