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hnswutils.c
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#include "postgres.h"
#include <math.h>
#include "access/generic_xlog.h"
#include "catalog/pg_type.h"
#include "catalog/pg_type_d.h"
#include "common/hashfn.h"
#include "fmgr.h"
#include "hnsw.h"
#include "lib/pairingheap.h"
#include "sparsevec.h"
#include "storage/bufmgr.h"
#include "utils/datum.h"
#include "utils/memdebug.h"
#include "utils/rel.h"
#if PG_VERSION_NUM < 170000
static inline uint64
murmurhash64(uint64 data)
{
uint64 h = data;
h ^= h >> 33;
h *= 0xff51afd7ed558ccd;
h ^= h >> 33;
h *= 0xc4ceb9fe1a85ec53;
h ^= h >> 33;
return h;
}
#endif
/* TID hash table */
static uint32
hash_tid(ItemPointerData tid)
{
union
{
uint64 i;
ItemPointerData tid;
} x;
/* Initialize unused bytes */
x.i = 0;
x.tid = tid;
return murmurhash64(x.i);
}
#define SH_PREFIX tidhash
#define SH_ELEMENT_TYPE TidHashEntry
#define SH_KEY_TYPE ItemPointerData
#define SH_KEY tid
#define SH_HASH_KEY(tb, key) hash_tid(key)
#define SH_EQUAL(tb, a, b) ItemPointerEquals(&a, &b)
#define SH_SCOPE extern
#define SH_DEFINE
#include "lib/simplehash.h"
/* Pointer hash table */
static uint32
hash_pointer(uintptr_t ptr)
{
#if SIZEOF_VOID_P == 8
return murmurhash64((uint64) ptr);
#else
return murmurhash32((uint32) ptr);
#endif
}
#define SH_PREFIX pointerhash
#define SH_ELEMENT_TYPE PointerHashEntry
#define SH_KEY_TYPE uintptr_t
#define SH_KEY ptr
#define SH_HASH_KEY(tb, key) hash_pointer(key)
#define SH_EQUAL(tb, a, b) (a == b)
#define SH_SCOPE extern
#define SH_DEFINE
#include "lib/simplehash.h"
/* Offset hash table */
static uint32
hash_offset(Size offset)
{
#if SIZEOF_SIZE_T == 8
return murmurhash64((uint64) offset);
#else
return murmurhash32((uint32) offset);
#endif
}
#define SH_PREFIX offsethash
#define SH_ELEMENT_TYPE OffsetHashEntry
#define SH_KEY_TYPE Size
#define SH_KEY offset
#define SH_HASH_KEY(tb, key) hash_offset(key)
#define SH_EQUAL(tb, a, b) (a == b)
#define SH_SCOPE extern
#define SH_DEFINE
#include "lib/simplehash.h"
/*
* Get the max number of connections in an upper layer for each element in the index
*/
int
HnswGetM(Relation index)
{
HnswOptions *opts = (HnswOptions *) index->rd_options;
if (opts)
return opts->m;
return HNSW_DEFAULT_M;
}
/*
* Get the size of the dynamic candidate list in the index
*/
int
HnswGetEfConstruction(Relation index)
{
HnswOptions *opts = (HnswOptions *) index->rd_options;
if (opts)
return opts->efConstruction;
return HNSW_DEFAULT_EF_CONSTRUCTION;
}
/*
* Get proc
*/
FmgrInfo *
HnswOptionalProcInfo(Relation index, uint16 procnum)
{
if (!OidIsValid(index_getprocid(index, 1, procnum)))
return NULL;
return index_getprocinfo(index, 1, procnum);
}
/*
* Init support functions
*/
void
HnswInitSupport(HnswSupport * support, Relation index)
{
support->procinfo = index_getprocinfo(index, 1, HNSW_DISTANCE_PROC);
support->collation = index->rd_indcollation[0];
support->normprocinfo = HnswOptionalProcInfo(index, HNSW_NORM_PROC);
}
/*
* Normalize value
*/
Datum
HnswNormValue(const HnswTypeInfo * typeInfo, Oid collation, Datum value)
{
return DirectFunctionCall1Coll(typeInfo->normalize, collation, value);
}
/*
* Check if non-zero norm
*/
bool
HnswCheckNorm(HnswSupport * support, Datum value)
{
return DatumGetFloat8(FunctionCall1Coll(support->normprocinfo, support->collation, value)) > 0;
}
/*
* New buffer
*/
Buffer
HnswNewBuffer(Relation index, ForkNumber forkNum)
{
Buffer buf = ReadBufferExtended(index, forkNum, P_NEW, RBM_NORMAL, NULL);
LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
return buf;
}
/*
* Init page
*/
void
HnswInitPage(Buffer buf, Page page)
{
PageInit(page, BufferGetPageSize(buf), sizeof(HnswPageOpaqueData));
HnswPageGetOpaque(page)->nextblkno = InvalidBlockNumber;
HnswPageGetOpaque(page)->page_id = HNSW_PAGE_ID;
}
/*
* Allocate a neighbor array
*/
HnswNeighborArray *
HnswInitNeighborArray(int lm, HnswAllocator * allocator)
{
HnswNeighborArray *a = HnswAlloc(allocator, HNSW_NEIGHBOR_ARRAY_SIZE(lm));
a->length = 0;
a->closerSet = false;
return a;
}
/*
* Allocate neighbors
*/
void
HnswInitNeighbors(char *base, HnswElement element, int m, HnswAllocator * allocator)
{
int level = element->level;
HnswNeighborArrayPtr *neighborList = (HnswNeighborArrayPtr *) HnswAlloc(allocator, sizeof(HnswNeighborArrayPtr) * (level + 1));
HnswPtrStore(base, element->neighbors, neighborList);
for (int lc = 0; lc <= level; lc++)
HnswPtrStore(base, neighborList[lc], HnswInitNeighborArray(HnswGetLayerM(m, lc), allocator));
}
/*
* Allocate memory from the allocator
*/
void *
HnswAlloc(HnswAllocator * allocator, Size size)
{
if (allocator)
return (*(allocator)->alloc) (size, (allocator)->state);
return palloc(size);
}
/*
* Allocate an element
*/
HnswElement
HnswInitElement(char *base, ItemPointer heaptid, int m, double ml, int maxLevel, HnswAllocator * allocator)
{
HnswElement element = HnswAlloc(allocator, sizeof(HnswElementData));
int level = (int) (-log(RandomDouble()) * ml);
/* Cap level */
if (level > maxLevel)
level = maxLevel;
element->heaptidsLength = 0;
HnswAddHeapTid(element, heaptid);
element->level = level;
element->deleted = 0;
/* Start at one to make it easier to find issues */
element->version = 1;
HnswInitNeighbors(base, element, m, allocator);
HnswPtrStore(base, element->value, (Pointer) NULL);
return element;
}
/*
* Add a heap TID to an element
*/
void
HnswAddHeapTid(HnswElement element, ItemPointer heaptid)
{
element->heaptids[element->heaptidsLength++] = *heaptid;
}
/*
* Allocate an element from block and offset numbers
*/
HnswElement
HnswInitElementFromBlock(BlockNumber blkno, OffsetNumber offno)
{
HnswElement element = palloc(sizeof(HnswElementData));
char *base = NULL;
element->blkno = blkno;
element->offno = offno;
HnswPtrStore(base, element->neighbors, (HnswNeighborArrayPtr *) NULL);
HnswPtrStore(base, element->value, (Pointer) NULL);
return element;
}
/*
* Get the metapage info
*/
void
HnswGetMetaPageInfo(Relation index, int *m, HnswElement * entryPoint)
{
Buffer buf;
Page page;
HnswMetaPage metap;
buf = ReadBuffer(index, HNSW_METAPAGE_BLKNO);
LockBuffer(buf, BUFFER_LOCK_SHARE);
page = BufferGetPage(buf);
metap = HnswPageGetMeta(page);
if (unlikely(metap->magicNumber != HNSW_MAGIC_NUMBER))
elog(ERROR, "hnsw index is not valid");
if (m != NULL)
*m = metap->m;
if (entryPoint != NULL)
{
if (BlockNumberIsValid(metap->entryBlkno))
{
*entryPoint = HnswInitElementFromBlock(metap->entryBlkno, metap->entryOffno);
(*entryPoint)->level = metap->entryLevel;
}
else
*entryPoint = NULL;
}
UnlockReleaseBuffer(buf);
}
/*
* Get the entry point
*/
HnswElement
HnswGetEntryPoint(Relation index)
{
HnswElement entryPoint;
HnswGetMetaPageInfo(index, NULL, &entryPoint);
return entryPoint;
}
/*
* Update the metapage info
*/
static void
HnswUpdateMetaPageInfo(Page page, int updateEntry, HnswElement entryPoint, BlockNumber insertPage)
{
HnswMetaPage metap = HnswPageGetMeta(page);
if (updateEntry)
{
if (entryPoint == NULL)
{
metap->entryBlkno = InvalidBlockNumber;
metap->entryOffno = InvalidOffsetNumber;
metap->entryLevel = -1;
}
else if (entryPoint->level > metap->entryLevel || updateEntry == HNSW_UPDATE_ENTRY_ALWAYS)
{
metap->entryBlkno = entryPoint->blkno;
metap->entryOffno = entryPoint->offno;
metap->entryLevel = entryPoint->level;
}
}
if (BlockNumberIsValid(insertPage))
metap->insertPage = insertPage;
}
/*
* Update the metapage
*/
void
HnswUpdateMetaPage(Relation index, int updateEntry, HnswElement entryPoint, BlockNumber insertPage, ForkNumber forkNum, bool building)
{
Buffer buf;
Page page;
GenericXLogState *state;
buf = ReadBufferExtended(index, forkNum, HNSW_METAPAGE_BLKNO, RBM_NORMAL, NULL);
LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
if (building)
{
state = NULL;
page = BufferGetPage(buf);
}
else
{
state = GenericXLogStart(index);
page = GenericXLogRegisterBuffer(state, buf, 0);
}
HnswUpdateMetaPageInfo(page, updateEntry, entryPoint, insertPage);
if (building)
MarkBufferDirty(buf);
else
GenericXLogFinish(state);
UnlockReleaseBuffer(buf);
}
/*
* Form index value
*/
bool
HnswFormIndexValue(Datum *out, Datum *values, bool *isnull, const HnswTypeInfo * typeInfo, HnswSupport * support)
{
/* Detoast once for all calls */
Datum value = PointerGetDatum(PG_DETOAST_DATUM(values[0]));
/* Check value */
if (typeInfo->checkValue != NULL)
typeInfo->checkValue(DatumGetPointer(value));
/* Normalize if needed */
if (support->normprocinfo != NULL)
{
if (!HnswCheckNorm(support, value))
return false;
value = HnswNormValue(typeInfo, support->collation, value);
}
*out = value;
return true;
}
/*
* Set element tuple, except for neighbor info
*/
void
HnswSetElementTuple(char *base, HnswElementTuple etup, HnswElement element)
{
Pointer valuePtr = HnswPtrAccess(base, element->value);
etup->type = HNSW_ELEMENT_TUPLE_TYPE;
etup->level = element->level;
etup->deleted = 0;
etup->version = element->version;
for (int i = 0; i < HNSW_HEAPTIDS; i++)
{
if (i < element->heaptidsLength)
etup->heaptids[i] = element->heaptids[i];
else
ItemPointerSetInvalid(&etup->heaptids[i]);
}
memcpy(&etup->data, valuePtr, VARSIZE_ANY(valuePtr));
}
/*
* Set neighbor tuple
*/
void
HnswSetNeighborTuple(char *base, HnswNeighborTuple ntup, HnswElement e, int m)
{
int idx = 0;
ntup->type = HNSW_NEIGHBOR_TUPLE_TYPE;
for (int lc = e->level; lc >= 0; lc--)
{
HnswNeighborArray *neighbors = HnswGetNeighbors(base, e, lc);
int lm = HnswGetLayerM(m, lc);
for (int i = 0; i < lm; i++)
{
ItemPointer indextid = &ntup->indextids[idx++];
if (i < neighbors->length)
{
HnswCandidate *hc = &neighbors->items[i];
HnswElement hce = HnswPtrAccess(base, hc->element);
ItemPointerSet(indextid, hce->blkno, hce->offno);
}
else
ItemPointerSetInvalid(indextid);
}
}
ntup->count = idx;
ntup->version = e->version;
}
/*
* Load an element from a tuple
*/
void
HnswLoadElementFromTuple(HnswElement element, HnswElementTuple etup, bool loadHeaptids, bool loadVec)
{
element->level = etup->level;
element->deleted = etup->deleted;
element->version = etup->version;
element->neighborPage = ItemPointerGetBlockNumber(&etup->neighbortid);
element->neighborOffno = ItemPointerGetOffsetNumber(&etup->neighbortid);
element->heaptidsLength = 0;
if (loadHeaptids)
{
for (int i = 0; i < HNSW_HEAPTIDS; i++)
{
/* Can stop at first invalid */
if (!ItemPointerIsValid(&etup->heaptids[i]))
break;
HnswAddHeapTid(element, &etup->heaptids[i]);
}
}
if (loadVec)
{
char *base = NULL;
Datum value = datumCopy(PointerGetDatum(&etup->data), false, -1);
HnswPtrStore(base, element->value, DatumGetPointer(value));
}
}
/*
* Calculate the distance between values
*/
static inline double
HnswGetDistance(Datum a, Datum b, HnswSupport * support)
{
return DatumGetFloat8(FunctionCall2Coll(support->procinfo, support->collation, a, b));
}
/*
* Load an element and optionally get its distance from q
*/
static void
HnswLoadElementImpl(BlockNumber blkno, OffsetNumber offno, double *distance, HnswQuery * q, Relation index, HnswSupport * support, bool loadVec, double *maxDistance, HnswElement * element)
{
Buffer buf;
Page page;
HnswElementTuple etup;
/* Read vector */
buf = ReadBuffer(index, blkno);
LockBuffer(buf, BUFFER_LOCK_SHARE);
page = BufferGetPage(buf);
etup = (HnswElementTuple) PageGetItem(page, PageGetItemId(page, offno));
Assert(HnswIsElementTuple(etup));
/* Calculate distance */
if (distance != NULL)
{
if (DatumGetPointer(q->value) == NULL)
*distance = 0;
else
*distance = HnswGetDistance(q->value, PointerGetDatum(&etup->data), support);
}
/* Load element */
if (distance == NULL || maxDistance == NULL || *distance < *maxDistance)
{
if (*element == NULL)
*element = HnswInitElementFromBlock(blkno, offno);
HnswLoadElementFromTuple(*element, etup, true, loadVec);
}
UnlockReleaseBuffer(buf);
}
/*
* Load an element and optionally get its distance from q
*/
void
HnswLoadElement(HnswElement element, double *distance, HnswQuery * q, Relation index, HnswSupport * support, bool loadVec, double *maxDistance)
{
HnswLoadElementImpl(element->blkno, element->offno, distance, q, index, support, loadVec, maxDistance, &element);
}
/*
* Get the distance for an element
*/
static double
GetElementDistance(char *base, HnswElement element, HnswQuery * q, HnswSupport * support)
{
Datum value = HnswGetValue(base, element);
return HnswGetDistance(q->value, value, support);
}
/*
* Allocate a search candidate
*/
static HnswSearchCandidate *
HnswInitSearchCandidate(char *base, HnswElement element, double distance)
{
HnswSearchCandidate *sc = palloc(sizeof(HnswSearchCandidate));
HnswPtrStore(base, sc->element, element);
sc->distance = distance;
return sc;
}
/*
* Create a candidate for the entry point
*/
HnswSearchCandidate *
HnswEntryCandidate(char *base, HnswElement entryPoint, HnswQuery * q, Relation index, HnswSupport * support, bool loadVec)
{
bool inMemory = index == NULL;
double distance;
if (inMemory)
distance = GetElementDistance(base, entryPoint, q, support);
else
HnswLoadElement(entryPoint, &distance, q, index, support, loadVec, NULL);
return HnswInitSearchCandidate(base, entryPoint, distance);
}
/*
* Compare candidate distances
*/
static int
CompareNearestCandidates(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
if (HnswGetSearchCandidateConst(c_node, a)->distance < HnswGetSearchCandidateConst(c_node, b)->distance)
return 1;
if (HnswGetSearchCandidateConst(c_node, a)->distance > HnswGetSearchCandidateConst(c_node, b)->distance)
return -1;
return 0;
}
/*
* Compare discarded candidate distances
*/
static int
CompareNearestDiscardedCandidates(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
if (HnswGetSearchCandidateConst(w_node, a)->distance < HnswGetSearchCandidateConst(w_node, b)->distance)
return 1;
if (HnswGetSearchCandidateConst(w_node, a)->distance > HnswGetSearchCandidateConst(w_node, b)->distance)
return -1;
return 0;
}
/*
* Compare candidate distances
*/
static int
CompareFurthestCandidates(const pairingheap_node *a, const pairingheap_node *b, void *arg)
{
if (HnswGetSearchCandidateConst(w_node, a)->distance < HnswGetSearchCandidateConst(w_node, b)->distance)
return -1;
if (HnswGetSearchCandidateConst(w_node, a)->distance > HnswGetSearchCandidateConst(w_node, b)->distance)
return 1;
return 0;
}
/*
* Init visited
*/
static inline void
InitVisited(char *base, visited_hash * v, bool inMemory, int ef, int m)
{
if (!inMemory)
v->tids = tidhash_create(CurrentMemoryContext, ef * m * 2, NULL);
else if (base != NULL)
v->offsets = offsethash_create(CurrentMemoryContext, ef * m * 2, NULL);
else
v->pointers = pointerhash_create(CurrentMemoryContext, ef * m * 2, NULL);
}
/*
* Add to visited
*/
static inline void
AddToVisited(char *base, visited_hash * v, HnswElementPtr elementPtr, bool inMemory, bool *found)
{
if (!inMemory)
{
HnswElement element = HnswPtrAccess(base, elementPtr);
ItemPointerData indextid;
ItemPointerSet(&indextid, element->blkno, element->offno);
tidhash_insert(v->tids, indextid, found);
}
else if (base != NULL)
{
HnswElement element = HnswPtrAccess(base, elementPtr);
offsethash_insert_hash(v->offsets, HnswPtrOffset(elementPtr), element->hash, found);
}
else
{
HnswElement element = HnswPtrAccess(base, elementPtr);
pointerhash_insert_hash(v->pointers, (uintptr_t) HnswPtrPointer(elementPtr), element->hash, found);
}
}
/*
* Count element towards ef
*/
static inline bool
CountElement(HnswElement skipElement, HnswElement e)
{
if (skipElement == NULL)
return true;
/* Ensure does not access heaptidsLength during in-memory build */
pg_memory_barrier();
/* Keep scan-build happy on Mac x86-64 */
Assert(e);
return e->heaptidsLength != 0;
}
/*
* Load unvisited neighbors from memory
*/
static void
HnswLoadUnvisitedFromMemory(char *base, HnswElement element, HnswUnvisited * unvisited, int *unvisitedLength, visited_hash * v, int lc, HnswNeighborArray * localNeighborhood, Size neighborhoodSize)
{
/* Get the neighborhood at layer lc */
HnswNeighborArray *neighborhood = HnswGetNeighbors(base, element, lc);
/* Copy neighborhood to local memory */
LWLockAcquire(&element->lock, LW_SHARED);
memcpy(localNeighborhood, neighborhood, neighborhoodSize);
LWLockRelease(&element->lock);
*unvisitedLength = 0;
for (int i = 0; i < localNeighborhood->length; i++)
{
HnswCandidate *hc = &localNeighborhood->items[i];
bool found;
AddToVisited(base, v, hc->element, true, &found);
if (!found)
unvisited[(*unvisitedLength)++].element = HnswPtrAccess(base, hc->element);
}
}
/*
* Load neighbor index TIDs
*/
bool
HnswLoadNeighborTids(HnswElement element, ItemPointerData *indextids, Relation index, int m, int lm, int lc)
{
Buffer buf;
Page page;
HnswNeighborTuple ntup;
int start;
buf = ReadBuffer(index, element->neighborPage);
LockBuffer(buf, BUFFER_LOCK_SHARE);
page = BufferGetPage(buf);
ntup = (HnswNeighborTuple) PageGetItem(page, PageGetItemId(page, element->neighborOffno));
/*
* Ensure the neighbor tuple has not been deleted or replaced between
* index scan iterations
*/
if (ntup->version != element->version || ntup->count != (element->level + 2) * m)
{
UnlockReleaseBuffer(buf);
return false;
}
/* Copy to minimize lock time */
start = (element->level - lc) * m;
memcpy(indextids, ntup->indextids + start, lm * sizeof(ItemPointerData));
UnlockReleaseBuffer(buf);
return true;
}
/*
* Load unvisited neighbors from disk
*/
static void
HnswLoadUnvisitedFromDisk(HnswElement element, HnswUnvisited * unvisited, int *unvisitedLength, visited_hash * v, Relation index, int m, int lm, int lc)
{
ItemPointerData indextids[HNSW_MAX_M * 2];
*unvisitedLength = 0;
if (!HnswLoadNeighborTids(element, indextids, index, m, lm, lc))
return;
for (int i = 0; i < lm; i++)
{
ItemPointer indextid = &indextids[i];
bool found;
if (!ItemPointerIsValid(indextid))
break;
tidhash_insert(v->tids, *indextid, &found);
if (!found)
unvisited[(*unvisitedLength)++].indextid = *indextid;
}
}
/*
* Algorithm 2 from paper
*/
List *
HnswSearchLayer(char *base, HnswQuery * q, List *ep, int ef, int lc, Relation index, HnswSupport * support, int m, bool inserting, HnswElement skipElement, visited_hash * v, pairingheap **discarded, bool initVisited, int64 *tuples)
{
List *w = NIL;
pairingheap *C = pairingheap_allocate(CompareNearestCandidates, NULL);
pairingheap *W = pairingheap_allocate(CompareFurthestCandidates, NULL);
int wlen = 0;
visited_hash vh;
ListCell *lc2;
HnswNeighborArray *localNeighborhood = NULL;
Size neighborhoodSize = 0;
int lm = HnswGetLayerM(m, lc);
HnswUnvisited *unvisited = palloc(lm * sizeof(HnswUnvisited));
int unvisitedLength;
bool inMemory = index == NULL;
if (v == NULL)
{
v = &vh;
initVisited = true;
}
if (initVisited)
{
InitVisited(base, v, inMemory, ef, m);
if (discarded != NULL)
*discarded = pairingheap_allocate(CompareNearestDiscardedCandidates, NULL);
}
/* Create local memory for neighborhood if needed */
if (inMemory)
{
neighborhoodSize = HNSW_NEIGHBOR_ARRAY_SIZE(lm);
localNeighborhood = palloc(neighborhoodSize);
}
/* Add entry points to v, C, and W */
foreach(lc2, ep)
{
HnswSearchCandidate *sc = (HnswSearchCandidate *) lfirst(lc2);
bool found;
if (initVisited)
{
AddToVisited(base, v, sc->element, inMemory, &found);
/* OK to count elements instead of tuples */
if (tuples != NULL)
(*tuples)++;
}
pairingheap_add(C, &sc->c_node);
pairingheap_add(W, &sc->w_node);
/*
* Do not count elements being deleted towards ef when vacuuming. It
* would be ideal to do this for inserts as well, but this could
* affect insert performance.
*/
if (CountElement(skipElement, HnswPtrAccess(base, sc->element)))
wlen++;
}
while (!pairingheap_is_empty(C))
{
HnswSearchCandidate *c = HnswGetSearchCandidate(c_node, pairingheap_remove_first(C));
HnswSearchCandidate *f = HnswGetSearchCandidate(w_node, pairingheap_first(W));
HnswElement cElement;
if (c->distance > f->distance)
break;
cElement = HnswPtrAccess(base, c->element);
if (inMemory)
HnswLoadUnvisitedFromMemory(base, cElement, unvisited, &unvisitedLength, v, lc, localNeighborhood, neighborhoodSize);
else
HnswLoadUnvisitedFromDisk(cElement, unvisited, &unvisitedLength, v, index, m, lm, lc);
/* OK to count elements instead of tuples */
if (tuples != NULL)
(*tuples) += unvisitedLength;
for (int i = 0; i < unvisitedLength; i++)
{
HnswElement eElement;
HnswSearchCandidate *e;
double eDistance;
bool alwaysAdd = wlen < ef;
f = HnswGetSearchCandidate(w_node, pairingheap_first(W));
if (inMemory)
{
eElement = unvisited[i].element;
eDistance = GetElementDistance(base, eElement, q, support);
}
else
{
ItemPointer indextid = &unvisited[i].indextid;
BlockNumber blkno = ItemPointerGetBlockNumber(indextid);
OffsetNumber offno = ItemPointerGetOffsetNumber(indextid);
/* Avoid any allocations if not adding */
eElement = NULL;
HnswLoadElementImpl(blkno, offno, &eDistance, q, index, support, inserting, alwaysAdd || discarded != NULL ? NULL : &f->distance, &eElement);
if (eElement == NULL)
continue;
}
if (eElement == NULL || !(eDistance < f->distance || alwaysAdd))
{
if (discarded != NULL)
{
/* Create a new candidate */
e = HnswInitSearchCandidate(base, eElement, eDistance);
pairingheap_add(*discarded, &e->w_node);
}
continue;
}
/* Make robust to issues */
if (eElement->level < lc)
continue;
/* Create a new candidate */
e = HnswInitSearchCandidate(base, eElement, eDistance);
pairingheap_add(C, &e->c_node);
pairingheap_add(W, &e->w_node);
/*
* Do not count elements being deleted towards ef when vacuuming.
* It would be ideal to do this for inserts as well, but this
* could affect insert performance.
*/
if (CountElement(skipElement, eElement))
{
wlen++;
/* No need to decrement wlen */
if (wlen > ef)
{
HnswSearchCandidate *d = HnswGetSearchCandidate(w_node, pairingheap_remove_first(W));
if (discarded != NULL)
pairingheap_add(*discarded, &d->w_node);
}
}
}
}
/* Add each element of W to w */
while (!pairingheap_is_empty(W))
{
HnswSearchCandidate *sc = HnswGetSearchCandidate(w_node, pairingheap_remove_first(W));
w = lappend(w, sc);
}
return w;
}
/*
* Compare candidate distances with pointer tie-breaker
*/
static int
CompareCandidateDistances(const ListCell *a, const ListCell *b)
{
HnswCandidate *hca = lfirst(a);
HnswCandidate *hcb = lfirst(b);
if (hca->distance < hcb->distance)
return 1;
if (hca->distance > hcb->distance)
return -1;
if (HnswPtrPointer(hca->element) < HnswPtrPointer(hcb->element))
return 1;
if (HnswPtrPointer(hca->element) > HnswPtrPointer(hcb->element))
return -1;
return 0;
}