MB-28163: Register a callback with context to estimate RAM for search

This callback if registered with context will invoke the api to estimate
the memory needed to execute a search query. The callback defined at
the client side will be responsible for determining whether to
continue with the search or abort based on the threshold settings.

index_impl.go

@@ -50,6 +50,10 @@ const storePath = "store"
 
 var mappingInternalKey = []byte("_mapping")
 
+const SearchMemCheckCallbackKey = "_search_mem_callback_key"
+
+type SearchMemCheckCallbackFn func(size uint64) error
+
 func indexStorePath(path string) string {
 	return path + string(os.PathSeparator) + storePath
 }
@@ -479,6 +483,15 @@ func (i *indexImpl) SearchInContext(ctx context.Context, req *SearchRequest) (sr
 		collector.SetFacetsBuilder(facetsBuilder)
 	}
 
+	if memCb := ctx.Value(SearchMemCheckCallbackKey); memCb != nil {
+		if memCbFn, ok := memCb.(SearchMemCheckCallbackFn); ok {
+			err = memCbFn(memNeededForSearch(req, searcher, collector))
+		}
+	}
+	if err != nil {
+		return nil, err
+	}
+
 	err = collector.Collect(ctx, searcher, indexReader)
 	if err != nil {
 		return nil, err

index_test.go

@@ -1870,3 +1870,50 @@ func BenchmarkUpsidedownSearchOverhead(b *testing.B) {
 func BenchmarkScorchSearchOverhead(b *testing.B) {
 	benchmarkSearchOverhead(scorch.Name, b)
 }
+
+func TestSearchMemCheckCallback(t *testing.T) {
+	defer func() {
+		err := os.RemoveAll("testidx")
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	index, err := New("testidx", NewIndexMapping())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		err := index.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	elements := []string{"air", "water", "fire", "earth"}
+	for j := 0; j < 10000; j++ {
+		err = index.Index(fmt.Sprintf("%d", j),
+			map[string]interface{}{"name": elements[j%len(elements)]})
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	query := NewTermQuery("water")
+	req := NewSearchRequest(query)
+
+	expErr := fmt.Errorf("MEM_LIMIT_EXCEEDED")
+	f := func(size uint64) error {
+		if size > 1000 {
+			return expErr
+		}
+		return nil
+	}
+
+	ctx := context.WithValue(context.Background(), SearchMemCheckCallbackKey,
+		SearchMemCheckCallbackFn(f))
+	_, err = index.SearchInContext(ctx, req)
+	if err != expErr {
+		t.Fatalf("Expected: %v, Got: %v", expErr, err)
+	}
+}