doc/policy.md

@@ -101,16 +101,16 @@ In a nutshell, a `SELECT` takes a filter result as input and outputs a specific
 Let's see some examples
 ```sql
 -- Selects exactly one node from the entire netmap
-SELECT 1 FROM *               
+SELECT 1 FROM *  
 
 -- Same as above, but with an identifier for the selection
-SELECT 1 FROM * AS ONE        
+SELECT 1 FROM * AS ONE  
 
--- Selects two nodes from the RedOrBlueNodes filter, such that both selected nodes 
+-- Selects two nodes from the RedOrBlueNodes filter, such that both selected nodes
 -- share the same value for the Color attribute, i.e. both red or both blue.
-SELECT 2 IN SAME Color FROM RedOrBlueNodes 
+SELECT 2 IN SAME Color FROM RedOrBlueNodes
 
--- Selects two nodes from the RedOrBlueNodes filter, such that the selected nodes 
+-- Selects two nodes from the RedOrBlueNodes filter, such that the selected nodes
 -- have distinct values for the Color attribute, i.e. one red and one blue.
 -- The selection is also given an identifier.
 SELECT 2 IN DISTINCT Color FROM RedOrBlueNodes AS MyNodes
@@ -131,7 +131,8 @@ Its basic syntax is as follows:
 REP <count> {IN <select>}
 ```
 
-If a select is not specified, then the entire netmap is used as input. The resulting nodes will be used to actually store objects and they constitute a replica group (or simply, "a replica").
+If a select is not specified, then the entire netmap is used as input. The only exception to this rule is when exactly 1 replica and 1 selector are being present: in this case the only selector is being used instead of the whole netmap.
+The resulting nodes will be used to actually store objects and they constitute a replica group (or simply, "a replica").
 
 Examples
 ```sql
@@ -173,18 +174,18 @@ In additional to this basic syntax, there are a couple of additional useful opti
 
 ### The policy playground
 
-> ℹ️ This section assumes you have an up-to-date version of the `frostfs-cli`. 
+> ℹ️ This section assumes you have an up-to-date version of the `frostfs-cli`.
 
 While simple placement policies have predictable results that can be understood at a glance, more complex ones need careful consideration before deployment. In order to simplify understanding a policy's outcome and experimenting while learning, a builtin tool is provided as part of the `frostfs-cli` for this purpose: the policy playground.
 
-For the remainder of this guide, we will use the policy playground to setup a virtual netmap (that is, one that doesn't require any networking or deployment) and test various policies. In order to visualize this netmap easily, each node will have three attributes: a character, a shape and a color 
+For the remainder of this guide, we will use the policy playground to setup a virtual netmap (that is, one that doesn't require any networking or deployment) and test various policies. In order to visualize this netmap easily, each node will have three attributes: a character, a shape and a color
 
 ![Sample Netmap](./image/sample_netmap.svg)
 
 We can start the policy playground as follows:
 ```sh
 $ frostfs-cli container policy-playground
-> 
+>
 ```
 
 Since we didn't pass any endpoint, the initial netmap is empty, which we can verify with the `ls` command (to list the nodes in the netmap):
@@ -400,7 +401,7 @@ FILTER Color EQ 'Green' AS GreenNodes
 #### Example #6
 ```sql
 REP 1 IN MyNodes
-REP 2 
+REP 2
 CBF 2
 SELECT 1 FROM CuteNodes AS MyNodes
 FILTER (Color EQ 'Blue') AND NOT (Shape EQ 'Circle' OR Shape EQ 'Square') AS CuteNodes
@@ -442,4 +443,4 @@ Others:
 - `ls`: list nodes in the current netmap and their attributes
 - `add`: add a node to the current netmap. If it already exists, it will be overwritten.
 - `remove`: remove a node from the current netmap.
-- `eval`: evaluate a placement policy on the current netmap.
+- `eval`: evaluate a placement policy on the current netmap.

netmap/netmap.go

@@ -238,7 +238,7 @@ func (m NetMap) ContainerNodes(p PlacementPolicy, pivot []byte) ([][]NodeInfo, e
 	// marked as used by earlier replicas.
 	for i := range p.replicas {
 		sName := p.replicas[i].GetSelector()
-		if sName == "" {
+		if sName == "" && !(len(p.replicas) == 1 && len(p.selectors) == 1) {
 			var s netmap.Selector
 			s.SetCount(p.replicas[i].GetCount())
 			s.SetFilter(mainFilterName)
@@ -258,6 +258,9 @@ func (m NetMap) ContainerNodes(p PlacementPolicy, pivot []byte) ([][]NodeInfo, e
 		}
 
 		if p.unique {
+			if c.processedSelectors[sName] == nil {
+				return nil, fmt.Errorf("selector not found: '%s'", sName)
+			}
 			nodes, err := c.getSelection(*c.processedSelectors[sName])
 			if err != nil {
 				return nil, err

netmap/policy.go

@@ -852,6 +852,7 @@ func (p *policyVisitor) VisitExpr(ctx *parser.ExprContext) any {
 // validatePolicy checks high-level constraints such as filter link in SELECT
 // being actually defined in FILTER section.
 func validatePolicy(p PlacementPolicy) error {
+	canOmitNames := len(p.selectors) == 1 && len(p.replicas) == 1
 	seenFilters := map[string]bool{}
 	expectedFilters := map[string]struct{}{}
 	for i := range p.filters {
@@ -865,7 +866,7 @@ func validatePolicy(p PlacementPolicy) error {
 
 	seenSelectors := map[string]*netmap.Selector{}
 	for i := range p.selectors {
-		if p.selectors[i].GetName() == "" {
+		if p.selectors[i].GetName() == "" && !canOmitNames {
 			return errUnnamedSelector
 		}
 		if flt := p.selectors[i].GetFilter(); flt != mainFilterName {
@@ -886,7 +887,7 @@ func validatePolicy(p PlacementPolicy) error {
 	expectedSelectors := map[string]struct{}{}
 	for i := range p.replicas {
 		selName := p.replicas[i].GetSelector()
-		if selName != "" {
+		if selName != "" || canOmitNames {
 			expectedSelectors[selName] = struct{}{}
 			if seenSelectors[selName] == nil {
 				return fmt.Errorf("%w: '%s'", errUnknownSelector, selName)

netmap/policy_decode_test.go

@@ -9,6 +9,9 @@ import (
 
 func TestDecodeString(t *testing.T) {
 	testCases := []string{
+		`REP 2
+CBF 2
+SELECT 2 FROM *`,
 		`REP 1 IN X
 CBF 1
 SELECT 2 IN SAME Location FROM * AS X`,
@@ -48,10 +51,11 @@ REP 1`,
 	}
 
 	invalidTestCases := map[string]error{
-		`?REP 1`:                     errSyntaxError,
+		`?REP 1`:                                errSyntaxError,
-		`REP 1 trailing garbage`:     errSyntaxError,
+		`REP 1 trailing garbage`:                errSyntaxError,
-		`REP 1 SELECT 4 FROM * `:     errUnnamedSelector,
+		`REP 1 REP 1 SELECT 4 FROM *`:           errUnnamedSelector,
-		`REP 1 SELECT 4 FROM * AS X`: errRedundantSelector,
+		`REP 1 SELECT 4 FROM * SELECT 1 FROM *`: errUnnamedSelector,
+		`REP 1 IN X SELECT 4 FROM *`:            errUnknownSelector,
 		`REP 1 IN X REP 2 SELECT 4 FROM * AS X FILTER 'UN-LOCODE' EQ 'RU LED' AS F`: errRedundantFilter,
 	}
 

netmap/selector_test.go

@@ -283,6 +283,55 @@ func TestPlacementPolicy_Unique(t *testing.T) {
 	}
 }
 
+func TestPlacementPolicy_SingleOmitNames(t *testing.T) {
+	nodes := []NodeInfo{
+		nodeInfoFromAttributes("ID", "1", "Country", "Russia", "City", "SPB"),
+		nodeInfoFromAttributes("ID", "2", "Country", "Germany", "City", "Berlin"),
+		nodeInfoFromAttributes("ID", "3", "Country", "Russia", "City", "Moscow"),
+		nodeInfoFromAttributes("ID", "4", "Country", "France", "City", "Paris"),
+		nodeInfoFromAttributes("ID", "5", "Country", "France", "City", "Lyon"),
+		nodeInfoFromAttributes("ID", "6", "Country", "Russia", "City", "SPB"),
+		nodeInfoFromAttributes("ID", "7", "Country", "Russia", "City", "Moscow"),
+		nodeInfoFromAttributes("ID", "8", "Country", "Germany", "City", "Darmstadt"),
+		nodeInfoFromAttributes("ID", "9", "Country", "Germany", "City", "Frankfurt"),
+		nodeInfoFromAttributes("ID", "10", "Country", "Russia", "City", "SPB"),
+		nodeInfoFromAttributes("ID", "11", "Country", "Russia", "City", "Moscow"),
+		nodeInfoFromAttributes("ID", "12", "Country", "Germany", "City", "London"),
+	}
+	for i := range nodes {
+		pub := make([]byte, 33)
+		rand.Read(pub)
+		nodes[i].SetPublicKey(pub)
+	}
+
+	var nm NetMap
+	nm.SetNodes(nodes)
+
+	for _, unique := range []bool{false, true} {
+		t.Run(fmt.Sprintf("unique=%t", unique), func(t *testing.T) {
+			ssNamed := []Selector{newSelector("X", "City", 2, "FromRU", (*Selector).SelectDistinct)}
+			fsNamed := []Filter{newFilter("FromRU", "Country", "Russia", netmap.EQ)}
+			rsNamed := []ReplicaDescriptor{newReplica(1, "X")}
+			pNamed := newPlacementPolicy(3, rsNamed, ssNamed, fsNamed)
+			pNamed.unique = unique
+
+			vNamed, err := nm.ContainerNodes(pNamed, []byte{1})
+			require.NoError(t, err)
+
+			ssUnnamed := []Selector{newSelector("", "City", 2, "FromRU", (*Selector).SelectDistinct)}
+			fsUnnamed := []Filter{newFilter("FromRU", "Country", "Russia", netmap.EQ)}
+			rsUnnamed := []ReplicaDescriptor{newReplica(1, "")}
+			pUnnamed := newPlacementPolicy(3, rsUnnamed, ssUnnamed, fsUnnamed)
+			pUnnamed.unique = unique
+
+			vUnnamed, err := nm.ContainerNodes(pUnnamed, []byte{1})
+			require.NoError(t, err)
+
+			require.Equal(t, vNamed, vUnnamed)
+		})
+	}
+}
+
 func TestPlacementPolicy_MultiREP(t *testing.T) {
 	nodes := []NodeInfo{
 		nodeInfoFromAttributes("ID", "1", "Country", "Russia", "City", "SPB"),