fix MatchNlist (#2401)

Signed-off-by: Nshengjun.li <shengjun.li@zilliz.com>

CHANGELOG.md

@@ -5,9 +5,11 @@ Please mark all change in change log and use the issue from GitHub
 
 ## Bug
 -   \#2378 Duplicate data after server restart
+-   \#2399 The nlist set by the user may not take effect
 
 ## Feature
 -   \#2363 Update branch version to 0.9.1
+-   \#2381 Upgrade to faiss_1.6.3
 
 ## Improvement
 -   \#2370 Clean compile warning

core/src/index/knowhere/knowhere/index/vector_index/ConfAdapter.cpp

@@ -75,14 +75,13 @@ ConfAdapter::CheckSearch(Config& oricfg, const IndexType type, const IndexMode m
 }
 
 int64_t
-MatchNlist(const int64_t& size, const int64_t& nlist, const int64_t& per_nlist) {
-    static float TYPICAL_COUNT = 1000000.0;
-    if (size <= TYPICAL_COUNT / per_nlist + 1) {
-        // handle less row count, avoid nlist set to 0
-        return 1;
-    } else if (int(size / TYPICAL_COUNT) * nlist <= 0) {
-        // calculate a proper nlist if nlist not specified or size less than TYPICAL_COUNT
-        return int(size / TYPICAL_COUNT * per_nlist);
+MatchNlist(int64_t size, int64_t nlist) {
+    const int64_t TYPICAL_COUNT = 1000000;
+    const int64_t PER_NLIST = 16384;
+
+    if (nlist * TYPICAL_COUNT > size * PER_NLIST) {
+        // nlist is too large, adjust to a proper value
+        nlist = std::max(1L, size * PER_NLIST / TYPICAL_COUNT);
     }
     return nlist;
 }
@@ -101,7 +100,7 @@ IVFConfAdapter::CheckTrain(Config& oricfg, const IndexMode mode) {
     // auto tune params
     int64_t nq = oricfg[knowhere::meta::ROWS].get<int64_t>();
     int64_t nlist = oricfg[knowhere::IndexParams::nlist].get<int64_t>();
-    oricfg[knowhere::IndexParams::nlist] = MatchNlist(nq, nlist, 16384);
+    oricfg[knowhere::IndexParams::nlist] = MatchNlist(nq, nlist);
 
     // Best Practice
     // static int64_t MIN_POINTS_PER_CENTROID = 40;
@@ -157,8 +156,8 @@ IVFPQConfAdapter::CheckTrain(Config& oricfg, const IndexMode mode) {
     // CheckIntByRange(knowhere::meta::ROWS, nlist, DEFAULT_MAX_ROWS);
 
     // auto tune params
-    oricfg[knowhere::IndexParams::nlist] = MatchNlist(oricfg[knowhere::meta::ROWS].get<int64_t>(),
-                                                      oricfg[knowhere::IndexParams::nlist].get<int64_t>(), 16384);
+    oricfg[knowhere::IndexParams::nlist] =
+        MatchNlist(oricfg[knowhere::meta::ROWS].get<int64_t>(), oricfg[knowhere::IndexParams::nlist].get<int64_t>());
 
     // Best Practice
     // static int64_t MIN_POINTS_PER_CENTROID = 40;
@@ -216,7 +215,7 @@ NSGConfAdapter::CheckTrain(Config& oricfg, const IndexMode mode) {
     CheckIntByRange(knowhere::IndexParams::candidate, MIN_CANDIDATE_POOL_SIZE, MAX_CANDIDATE_POOL_SIZE);
 
     // auto tune params
-    oricfg[knowhere::IndexParams::nlist] = MatchNlist(oricfg[knowhere::meta::ROWS].get<int64_t>(), 8192, 8192);
+    oricfg[knowhere::IndexParams::nlist] = MatchNlist(oricfg[knowhere::meta::ROWS].get<int64_t>(), 8192);
 
     int64_t nprobe = int(oricfg[knowhere::IndexParams::nlist].get<int64_t>() * 0.1);
     oricfg[knowhere::IndexParams::nprobe] = nprobe < 1 ? 1 : nprobe;

core/src/index/knowhere/knowhere/index/vector_index/ConfAdapter.h

@@ -11,6 +11,7 @@
 
 #pragma once
 
+#include <algorithm>
 #include <memory>
 #include <vector>