Added time budget for HNSW index scans

src/hnsw.c

@@ -18,6 +18,7 @@
 #endif
 
 int			hnsw_ef_search;
+int			hnsw_time_budget;
 int			hnsw_lock_tranche_id;
 static relopt_kind hnsw_relopt_kind;
 
@@ -68,6 +69,10 @@ HnswInit(void)
 							"Valid range is 1..1000.", &hnsw_ef_search,
 							HNSW_DEFAULT_EF_SEARCH, HNSW_MIN_EF_SEARCH, HNSW_MAX_EF_SEARCH, PGC_USERSET, 0, NULL, NULL, NULL);
 
+	DefineCustomIntVariable("hnsw.time_budget", "Sets the time budget for search",
+							NULL, &hnsw_time_budget,
+							-1, -1, INT_MAX, PGC_USERSET, GUC_UNIT_MS, NULL, NULL, NULL);
+
 	MarkGUCPrefixReserved("hnsw");
 }
 

src/hnsw.h

@@ -106,6 +106,7 @@
 
 /* Variables */
 extern int	hnsw_ef_search;
+extern int	hnsw_time_budget;
 extern int	hnsw_lock_tranche_id;
 
 typedef struct HnswElementData HnswElementData;
@@ -330,6 +331,7 @@ typedef struct HnswScanOpaqueData
 	bool		first;
 	List	   *w;
 	MemoryContext tmpCtx;
+	instr_time	start;
 
 	/* Support functions */
 	FmgrInfo   *procinfo;
@@ -374,7 +376,7 @@ bool		HnswCheckNorm(FmgrInfo *procinfo, Oid collation, Datum value);
 Buffer		HnswNewBuffer(Relation index, ForkNumber forkNum);
 void		HnswInitPage(Buffer buf, Page page);
 void		HnswInit(void);
-List	   *HnswSearchLayer(char *base, Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *procinfo, Oid collation, int m, bool inserting, HnswElement skipElement);
+List	   *HnswSearchLayer(char *base, Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *procinfo, Oid collation, int m, bool inserting, HnswElement skipElement, instr_time *start);
 HnswElement HnswGetEntryPoint(Relation index);
 void		HnswGetMetaPageInfo(Relation index, int *m, HnswElement * entryPoint);
 void	   *HnswAlloc(HnswAllocator * allocator, Size size);

src/hnswscan.c

@@ -3,6 +3,7 @@
 #include "access/relscan.h"
 #include "hnsw.h"
 #include "pgstat.h"
+#include "portability/instr_time.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "utils/memutils.h"
@@ -33,11 +34,11 @@ GetScanItems(IndexScanDesc scan, Datum q)
 
 	for (int lc = entryPoint->level; lc >= 1; lc--)
 	{
-		w = HnswSearchLayer(base, q, ep, 1, lc, index, procinfo, collation, m, false, NULL);
+		w = HnswSearchLayer(base, q, ep, 1, lc, index, procinfo, collation, m, false, NULL, &so->start);
 		ep = w;
 	}
 
-	return HnswSearchLayer(base, q, ep, hnsw_ef_search, 0, index, procinfo, collation, m, false, NULL);
+	return HnswSearchLayer(base, q, ep, hnsw_ef_search, 0, index, procinfo, collation, m, false, NULL, &so->start);
 }
 
 /*
@@ -90,6 +91,9 @@ hnswbeginscan(Relation index, int nkeys, int norderbys)
 	so->normprocinfo = HnswOptionalProcInfo(index, HNSW_NORM_PROC);
 	so->collation = index->rd_indcollation[0];
 
+	if (hnsw_time_budget != -1)
+		INSTR_TIME_SET_CURRENT(so->start);
+
 	scan->opaque = so;
 
 	return scan;

src/hnswutils.c

@@ -9,6 +9,7 @@
 #include "fmgr.h"
 #include "hnsw.h"
 #include "lib/pairingheap.h"
+#include "portability/instr_time.h"
 #include "sparsevec.h"
 #include "storage/bufmgr.h"
 #include "utils/datum.h"
@@ -799,7 +800,7 @@ HnswLoadUnvisitedFromDisk(HnswElement element, HnswUnvisited * unvisited, int *u
  * Algorithm 2 from paper
  */
 List *
-HnswSearchLayer(char *base, Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *procinfo, Oid collation, int m, bool inserting, HnswElement skipElement)
+HnswSearchLayer(char *base, Datum q, List *ep, int ef, int lc, Relation index, FmgrInfo *procinfo, Oid collation, int m, bool inserting, HnswElement skipElement, instr_time *start)
 {
 	List	   *w = NIL;
 	pairingheap *C = pairingheap_allocate(CompareNearestCandidates, NULL);
@@ -850,6 +851,17 @@ HnswSearchLayer(char *base, Datum q, List *ep, int ef, int lc, Relation index, F
 		HnswCandidate *f = HnswGetPairingHeapCandidate(w_node, pairingheap_first(W));
 		HnswElement cElement;
 
+		/* Check time budget */
+		if (hnsw_time_budget != -1)
+		{
+			instr_time	duration;
+
+			INSTR_TIME_SET_CURRENT(duration);
+			INSTR_TIME_SUBTRACT(duration, *start);
+			if (INSTR_TIME_GET_MILLISEC(duration) >= hnsw_time_budget)
+				break;
+		}
+
 		if (c->distance > f->distance)
 			break;
 
@@ -1291,7 +1303,7 @@ HnswFindElementNeighbors(char *base, HnswElement element, HnswElement entryPoint
 	/* 1st phase: greedy search to insert level */
 	for (int lc = entryLevel; lc >= level + 1; lc--)
 	{
-		w = HnswSearchLayer(base, q, ep, 1, lc, index, procinfo, collation, m, true, skipElement);
+		w = HnswSearchLayer(base, q, ep, 1, lc, index, procinfo, collation, m, true, skipElement, NULL);
 		ep = w;
 	}
 
@@ -1309,7 +1321,7 @@ HnswFindElementNeighbors(char *base, HnswElement element, HnswElement entryPoint
 		List	   *neighbors;
 		List	   *lw;
 
-		w = HnswSearchLayer(base, q, ep, efConstruction, lc, index, procinfo, collation, m, true, skipElement);
+		w = HnswSearchLayer(base, q, ep, efConstruction, lc, index, procinfo, collation, m, true, skipElement, NULL);
 
 		/* Elements being deleted or skipped can help with search */
 		/* but should be removed before selecting neighbors */