From 889af91faa82bb03216809b3d32cf1b5368a5f65 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Tue, 29 Aug 2023 21:53:02 +0200
Subject: [PATCH 01/22] wip

---
 integration/commands_diagnostic_test.go |   8 +-
 internal/handlers/sqlite/msg_getlog.go  | 134 +++++++++++++++++++++++-
 2 files changed, 136 insertions(+), 6 deletions(-)

diff --git a/integration/commands_diagnostic_test.go b/integration/commands_diagnostic_test.go
index f49768b77b03..c03a278b1c9f 100644
--- a/integration/commands_diagnostic_test.go
+++ b/integration/commands_diagnostic_test.go
@@ -186,14 +186,12 @@ func TestCommandsDiagnosticGetLog(t *testing.T) {
 		},
 	} {
 		name, tc := name, tc
-		t.Run(name, func(tt *testing.T) {
+		t.Run(name, func(t *testing.T) {
 			if tc.skip != "" {
-				tt.Skip(tc.skip)
+				t.Skip(tc.skip)
 			}
 
-			tt.Parallel()
-
-			t := setup.FailsForSQLite(tt, "https://github.com/FerretDB/FerretDB/issues/3261")
+			t.Parallel()
 
 			require.NotNil(t, tc.command, "command must not be nil")
 
diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index b5854cca1533..9653ed0136b3 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -16,12 +16,144 @@ package sqlite
 
 import (
 	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"time"
 
+	"go.uber.org/zap"
+
+	"github.com/FerretDB/FerretDB/build/version"
+	"github.com/FerretDB/FerretDB/internal/handlers/commonerrors"
+	"github.com/FerretDB/FerretDB/internal/handlers/commonparams"
+	"github.com/FerretDB/FerretDB/internal/types"
+	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
+	"github.com/FerretDB/FerretDB/internal/util/logging"
 	"github.com/FerretDB/FerretDB/internal/util/must"
 	"github.com/FerretDB/FerretDB/internal/wire"
 )
 
 // MsgGetLog implements HandlerInterface.
 func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg, error) {
-	return nil, notImplemented(must.NotFail(msg.Document()).Command())
+	document, err := msg.Document()
+	if err != nil {
+		return nil, lazyerrors.Error(err)
+	}
+
+	command := document.Command()
+
+	getLog, err := document.Get(command)
+	if err != nil {
+		return nil, lazyerrors.Error(err)
+	}
+
+	if _, ok := getLog.(types.NullType); ok {
+		return nil, commonerrors.NewCommandErrorMsg(
+			commonerrors.ErrMissingField,
+			`BSON field 'getLog.getLog' is missing but a required field`,
+		)
+	}
+
+	if _, ok := getLog.(string); !ok {
+		return nil, commonerrors.NewCommandError(
+			commonerrors.ErrTypeMismatch,
+			fmt.Errorf(
+				"BSON field 'getLog.getLog' is the wrong type '%s', expected type 'string'",
+				commonparams.AliasFromType(getLog),
+			),
+		)
+	}
+
+	var resDoc *types.Document
+
+	switch getLog {
+	case "*":
+		resDoc = must.NotFail(types.NewDocument(
+			"names", must.NotFail(types.NewArray("global", "startupWarnings")),
+			"ok", float64(1),
+		))
+
+	case "global":
+		log, err := logging.RecentEntries.GetArray(zap.DebugLevel)
+		if err != nil {
+			return nil, lazyerrors.Error(err)
+		}
+		resDoc = must.NotFail(types.NewDocument(
+			"log", log,
+			"totalLinesWritten", int64(log.Len()),
+			"ok", float64(1),
+		))
+
+	case "startupWarnings":
+		state := h.StateProvider.Get()
+
+		info := version.Get()
+
+		// it may be empty if no connection was established yet
+		hv, _, _ := strings.Cut(state.HandlerVersion, " ")
+		if hv != "" {
+			hv = " " + hv
+		}
+
+		startupWarnings := []string{
+			"Powered by FerretDB " + info.Version + " and PostgreSQL" + hv + ".",
+			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
+		}
+
+		switch {
+		case state.Telemetry == nil:
+			startupWarnings = append(
+				startupWarnings,
+				"The telemetry state is undecided.",
+				"Read more about FerretDB telemetry and how to opt out at https://beacon.ferretdb.io.",
+			)
+		case state.UpdateAvailable:
+			startupWarnings = append(
+				startupWarnings,
+				fmt.Sprintf(
+					"A new version available! The latest version: %s. The current version: %s.",
+					state.LatestVersion, info.Version,
+				),
+			)
+		}
+
+		var log types.Array
+
+		for _, line := range startupWarnings {
+			b, err := json.Marshal(map[string]any{
+				"msg":  line,
+				"tags": []string{"startupWarnings"},
+				"s":    "I",
+				"c":    "STORAGE",
+				"id":   42000,
+				"ctx":  "initandlisten",
+				"t": map[string]string{
+					"$date": time.Now().UTC().Format("2006-01-02T15:04:05.999Z07:00"),
+				},
+			})
+			if err != nil {
+				return nil, lazyerrors.Error(err)
+			}
+
+			log.Append(string(b))
+		}
+		resDoc = must.NotFail(types.NewDocument(
+			"log", &log,
+			"totalLinesWritten", int64(log.Len()),
+			"ok", float64(1),
+		))
+
+	default:
+		return nil, commonerrors.NewCommandError(
+			commonerrors.ErrOperationFailed,
+			fmt.Errorf("no RecentEntries named: %s", getLog),
+		)
+	}
+
+	var reply wire.OpMsg
+	must.NoError(reply.SetSections(wire.OpMsgSection{
+		Documents: []*types.Document{resDoc},
+	}))
+
+	return &reply, nil
 }

From ffd5e29df901a33e7059ce59dfeb67385c5f5442 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Tue, 29 Aug 2023 21:57:13 +0200
Subject: [PATCH 02/22] wip

---
 internal/handlers/sqlite/msg_getlog.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 9653ed0136b3..238c67a5c4d1 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -96,7 +96,7 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 		}
 
 		startupWarnings := []string{
-			"Powered by FerretDB " + info.Version + " and PostgreSQL" + hv + ".",
+			"Powered by FerretDB " + info.Version + " and SQLite" + hv + ".",
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 

From f00dc3ba4f5e8b97a36ab9036a27c12c3eae3ec2 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 09:22:17 +0200
Subject: [PATCH 03/22] no handler version for SQLite

---
 internal/handlers/sqlite/msg_getlog.go | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 238c67a5c4d1..6aea92293f18 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -18,7 +18,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"strings"
 	"time"
 
 	"go.uber.org/zap"
@@ -89,14 +88,8 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 
 		info := version.Get()
 
-		// it may be empty if no connection was established yet
-		hv, _, _ := strings.Cut(state.HandlerVersion, " ")
-		if hv != "" {
-			hv = " " + hv
-		}
-
 		startupWarnings := []string{
-			"Powered by FerretDB " + info.Version + " and SQLite" + hv + ".",
+			"Powered by FerretDB " + info.Version + " and SQLite.",
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 

From cb69450b7f6d9c0d49d22708e350cabc5a6fb276 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 12:54:13 +0200
Subject: [PATCH 04/22] wip

---
 internal/backends/backend.go            | 13 ++++++++++++
 internal/backends/postgresql/backend.go | 21 +++++++++++++++----
 internal/backends/sqlite/backend.go     | 19 +++++++++++++----
 internal/handlers/registry/newpg.go     |  2 +-
 internal/handlers/registry/sqlite.go    |  2 +-
 internal/handlers/sqlite/msg_getlog.go  |  3 ++-
 internal/handlers/sqlite/sqlite.go      | 28 ++++++++++++++++++-------
 7 files changed, 70 insertions(+), 18 deletions(-)

diff --git a/internal/backends/backend.go b/internal/backends/backend.go
index 850d4d1c677b..7a00300203b9 100644
--- a/internal/backends/backend.go
+++ b/internal/backends/backend.go
@@ -38,12 +38,20 @@ type Backend interface {
 	ListDatabases(context.Context, *ListDatabasesParams) (*ListDatabasesResult, error)
 	DropDatabase(context.Context, *DropDatabaseParams) error
 
+	Info() *Info
+
 	prometheus.Collector
 
 	// There is no interface method to create a database; see package documentation.
 	// TODO https://github.com/FerretDB/FerretDB/issues/3069
 }
 
+// Info represents information about a backend.
+type Info struct {
+	Name    string
+	Version string
+}
+
 // backendContract implements Backend interface.
 type backendContract struct {
 	b     Backend
@@ -132,6 +140,11 @@ func (bc *backendContract) DropDatabase(ctx context.Context, params *DropDatabas
 	return err
 }
 
+// Info returns information about the backend.
+func (bc *backendContract) Info() *Info {
+	return bc.b.Info()
+}
+
 // Describe implements prometheus.Collector.
 func (bc *backendContract) Describe(ch chan<- *prometheus.Desc) {
 	bc.b.Describe(ch)
diff --git a/internal/backends/postgresql/backend.go b/internal/backends/postgresql/backend.go
index cc3181253540..31db075e53ad 100644
--- a/internal/backends/postgresql/backend.go
+++ b/internal/backends/postgresql/backend.go
@@ -24,19 +24,24 @@ import (
 )
 
 // backend implements backends.Backend interface.
-type backend struct{}
+type backend struct {
+	version string
+}
 
 // NewBackendParams represents the parameters of NewBackend function.
 //
 //nolint:vet // for readability
 type NewBackendParams struct {
-	URI string
-	L   *zap.Logger
+	URI     string
+	L       *zap.Logger
+	Version string
 }
 
 // NewBackend creates a new backend for PostgreSQL-compatible database.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	return backends.BackendContract(new(backend)), nil
+	return backends.BackendContract(&backend{
+		version: params.Version,
+	}), nil
 }
 
 // Close implements backends.Backend interface.
@@ -60,6 +65,14 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 	panic("not implemented")
 }
 
+// Info implements backends.Backend interface.
+func (b *backend) Info() *backends.Info {
+	return &backends.Info{
+		Name:    "PostgreSQL",
+		Version: b.version,
+	}
+}
+
 // Describe implements prometheus.Collector.
 func (b *backend) Describe(ch chan<- *prometheus.Desc) {
 	panic("not implemented")
diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index afacce1e2b73..98004f478b21 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -26,15 +26,17 @@ import (
 
 // backend implements backends.Backend interface.
 type backend struct {
-	r *metadata.Registry
+	r       *metadata.Registry
+	version string // FIXME: set when connect?
 }
 
 // NewBackendParams represents the parameters of NewBackend function.
 //
 //nolint:vet // for readability
 type NewBackendParams struct {
-	URI string
-	L   *zap.Logger
+	URI     string
+	L       *zap.Logger
+	Version string
 }
 
 // NewBackend creates a new SQLite backend.
@@ -45,7 +47,8 @@ func NewBackend(params *NewBackendParams) (backends.Backend, error) {
 	}
 
 	return backends.BackendContract(&backend{
-		r: r,
+		r:       r,
+		version: params.Version,
 	}), nil
 }
 
@@ -84,6 +87,14 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 	return nil
 }
 
+// Info implements backends.Backend interface.
+func (b *backend) Info() *backends.Info {
+	return &backends.Info{
+		Name:    "SQLite",
+		Version: b.version,
+	}
+}
+
 // Describe implements prometheus.Collector.
 func (b *backend) Describe(ch chan<- *prometheus.Desc) {
 	b.r.Describe(ch)
diff --git a/internal/handlers/registry/newpg.go b/internal/handlers/registry/newpg.go
index 31b470c2c1d3..b6e3f5feaf97 100644
--- a/internal/handlers/registry/newpg.go
+++ b/internal/handlers/registry/newpg.go
@@ -27,7 +27,7 @@ func init() {
 		opts.Logger.Warn("New PostgreSQL backend is in alpha.")
 
 		handlerOpts := &sqlite.NewOpts{
-			Backend: "postgresql",
+			Backend: sqlite.PostgreSQL,
 			URI:     opts.PostgreSQLURL,
 
 			L:             opts.Logger.Named("postgresql"),
diff --git a/internal/handlers/registry/sqlite.go b/internal/handlers/registry/sqlite.go
index 2ebb97299e22..c1bbbaaed43c 100644
--- a/internal/handlers/registry/sqlite.go
+++ b/internal/handlers/registry/sqlite.go
@@ -25,7 +25,7 @@ func init() {
 		opts.Logger.Warn("SQLite backend is in beta.")
 
 		handlerOpts := &sqlite.NewOpts{
-			Backend: "sqlite",
+			Backend: sqlite.SQLite,
 			URI:     opts.SQLiteURL,
 
 			L:             opts.Logger.Named("sqlite"),
diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 6aea92293f18..abcd0495623d 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -87,9 +87,10 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 		state := h.StateProvider.Get()
 
 		info := version.Get()
+		backend := h.b.Info()
 
 		startupWarnings := []string{
-			"Powered by FerretDB " + info.Version + " and SQLite.",
+			fmt.Sprintf("Powered by FerretDB %s and %s %s.", info.Version, backend.Name, backend.Version),
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 
diff --git a/internal/handlers/sqlite/sqlite.go b/internal/handlers/sqlite/sqlite.go
index 0e2486f712bf..03bde253f953 100644
--- a/internal/handlers/sqlite/sqlite.go
+++ b/internal/handlers/sqlite/sqlite.go
@@ -48,12 +48,24 @@ type Handler struct {
 	cursors *cursor.Registry
 }
 
+// Backend represents backend type.
+type Backend string
+
+const (
+	// PostgreSQL represents PostgreSQL backend.
+	PostgreSQL Backend = "postgresql"
+
+	// SQLite represents SQLite backend.
+	SQLite Backend = "sqlite"
+)
+
 // NewOpts represents handler configuration.
 //
 //nolint:vet // for readability
 type NewOpts struct {
-	Backend string
+	Backend Backend
 	URI     string
+	Version string
 
 	L             *zap.Logger
 	ConnMetrics   *connmetrics.ConnMetrics
@@ -69,15 +81,17 @@ func New(opts *NewOpts) (handlers.Interface, error) {
 	var err error
 
 	switch opts.Backend {
-	case "postgresql":
+	case PostgreSQL:
 		b, err = postgresql.NewBackend(&postgresql.NewBackendParams{
-			URI: opts.URI,
-			L:   opts.L,
+			URI:     opts.URI,
+			L:       opts.L,
+			Version: opts.Version,
 		})
-	case "sqlite":
+	case SQLite:
 		b, err = sqlite.NewBackend(&sqlite.NewBackendParams{
-			URI: opts.URI,
-			L:   opts.L,
+			URI:     opts.URI,
+			L:       opts.L,
+			Version: opts.Version,
 		})
 	default:
 		panic("unknown backend: " + opts.Backend)

From 6b13139233d82bbdcca6da4ac7f784d8e5eadb54 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 15:23:15 +0200
Subject: [PATCH 05/22] wip

---
 internal/backends/postgresql/backend.go       |  5 +--
 internal/backends/sqlite/backend.go           | 11 +++----
 internal/backends/sqlite/metadata/registry.go | 31 ++++++++++++++++---
 .../backends/sqlite/metadata/registry_test.go | 12 ++++---
 internal/handlers/registry/sqlite.go          |  2 +-
 internal/handlers/sqlite/sqlite.go            | 28 +++++------------
 6 files changed, 48 insertions(+), 41 deletions(-)

diff --git a/internal/backends/postgresql/backend.go b/internal/backends/postgresql/backend.go
index 31db075e53ad..c1369b5d77e4 100644
--- a/internal/backends/postgresql/backend.go
+++ b/internal/backends/postgresql/backend.go
@@ -67,10 +67,7 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 
 // Info implements backends.Backend interface.
 func (b *backend) Info() *backends.Info {
-	return &backends.Info{
-		Name:    "PostgreSQL",
-		Version: b.version,
-	}
+	panic("not implemented")
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index 98004f478b21..6481dfa6c23d 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -27,28 +27,27 @@ import (
 // backend implements backends.Backend interface.
 type backend struct {
 	r       *metadata.Registry
-	version string // FIXME: set when connect?
+	version string
 }
 
 // NewBackendParams represents the parameters of NewBackend function.
 //
 //nolint:vet // for readability
 type NewBackendParams struct {
-	URI     string
-	L       *zap.Logger
-	Version string
+	URI string
+	L   *zap.Logger
 }
 
 // NewBackend creates a new SQLite backend.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	r, err := metadata.NewRegistry(params.URI, params.L)
+	r, version, err := metadata.NewRegistry(params.URI, params.L)
 	if err != nil {
 		return nil, err
 	}
 
 	return backends.BackendContract(&backend{
 		r:       r,
-		version: params.Version,
+		version: version,
 	}), nil
 }
 
diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 781ea3f04d5f..802610fec987 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -65,10 +65,12 @@ type Registry struct {
 }
 
 // NewRegistry creates a registry for SQLite databases in the directory specified by SQLite URI.
-func NewRegistry(u string, l *zap.Logger) (*Registry, error) {
+//
+// As the second return value, it returns the version of SQLite.
+func NewRegistry(u string, l *zap.Logger) (*Registry, string, error) {
 	p, initDBs, err := pool.New(u, l)
 	if err != nil {
-		return nil, err
+		return nil, "", err
 	}
 
 	r := &Registry{
@@ -77,14 +79,35 @@ func NewRegistry(u string, l *zap.Logger) (*Registry, error) {
 		colls: map[string]map[string]*Collection{},
 	}
 
+	var ver string
 	for name, db := range initDBs {
 		if err = r.initCollections(context.Background(), name, db); err != nil {
 			r.Close()
-			return nil, lazyerrors.Error(err)
+			return nil, "", lazyerrors.Error(err)
+		}
+
+		// query version for the first DB only
+		if ver == "" {
+			if ver, err = version(db); err != nil {
+				r.Close()
+				return nil, "", lazyerrors.Error(err)
+			}
 		}
 	}
 
-	return r, nil
+	return r, ver, nil
+}
+
+// version returns SQLite version.
+func version(db *fsql.DB) (string, error) {
+	row := db.QueryRowContext(context.Background(), "SELECT sqlite_version()")
+
+	var version string
+	if err := row.Scan(&version); err != nil {
+		return "", lazyerrors.Error(err)
+	}
+
+	return version, nil
 }
 
 // Close closes the registry.
diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index dc5ac4a3739d..856e1cbb2de4 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -71,8 +71,10 @@ func TestCreateDrop(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
-	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
+	r, version, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
 	require.NoError(t, err)
+	require.Equal(t, "3.35.5", version)
+
 	t.Cleanup(r.Close)
 
 	dbName := t.Name()
@@ -100,7 +102,7 @@ func TestCreateDropStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, _, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -139,7 +141,7 @@ func TestCreateSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, _, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -203,7 +205,7 @@ func TestDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, _, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -252,7 +254,7 @@ func TestCreateDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, _, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
diff --git a/internal/handlers/registry/sqlite.go b/internal/handlers/registry/sqlite.go
index c1bbbaaed43c..2ebb97299e22 100644
--- a/internal/handlers/registry/sqlite.go
+++ b/internal/handlers/registry/sqlite.go
@@ -25,7 +25,7 @@ func init() {
 		opts.Logger.Warn("SQLite backend is in beta.")
 
 		handlerOpts := &sqlite.NewOpts{
-			Backend: sqlite.SQLite,
+			Backend: "sqlite",
 			URI:     opts.SQLiteURL,
 
 			L:             opts.Logger.Named("sqlite"),
diff --git a/internal/handlers/sqlite/sqlite.go b/internal/handlers/sqlite/sqlite.go
index 03bde253f953..0e2486f712bf 100644
--- a/internal/handlers/sqlite/sqlite.go
+++ b/internal/handlers/sqlite/sqlite.go
@@ -48,24 +48,12 @@ type Handler struct {
 	cursors *cursor.Registry
 }
 
-// Backend represents backend type.
-type Backend string
-
-const (
-	// PostgreSQL represents PostgreSQL backend.
-	PostgreSQL Backend = "postgresql"
-
-	// SQLite represents SQLite backend.
-	SQLite Backend = "sqlite"
-)
-
 // NewOpts represents handler configuration.
 //
 //nolint:vet // for readability
 type NewOpts struct {
-	Backend Backend
+	Backend string
 	URI     string
-	Version string
 
 	L             *zap.Logger
 	ConnMetrics   *connmetrics.ConnMetrics
@@ -81,17 +69,15 @@ func New(opts *NewOpts) (handlers.Interface, error) {
 	var err error
 
 	switch opts.Backend {
-	case PostgreSQL:
+	case "postgresql":
 		b, err = postgresql.NewBackend(&postgresql.NewBackendParams{
-			URI:     opts.URI,
-			L:       opts.L,
-			Version: opts.Version,
+			URI: opts.URI,
+			L:   opts.L,
 		})
-	case SQLite:
+	case "sqlite":
 		b, err = sqlite.NewBackend(&sqlite.NewBackendParams{
-			URI:     opts.URI,
-			L:       opts.L,
-			Version: opts.Version,
+			URI: opts.URI,
+			L:   opts.L,
 		})
 	default:
 		panic("unknown backend: " + opts.Backend)

From 9e7c7a2b4c11504f72ecb7571aa83e94ca975734 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 15:55:52 +0200
Subject: [PATCH 06/22] wip

---
 internal/backends/backend.go                  |  8 ++--
 internal/backends/postgresql/backend.go       | 15 +++----
 internal/backends/sqlite/backend.go           | 20 +++++----
 .../backends/sqlite/metadata/pool/pool.go     | 17 +++++++
 internal/backends/sqlite/metadata/registry.go | 45 ++++++++-----------
 .../backends/sqlite/metadata/registry_test.go | 12 +++--
 internal/handlers/sqlite/msg_getlog.go        |  6 ++-
 7 files changed, 66 insertions(+), 57 deletions(-)

diff --git a/internal/backends/backend.go b/internal/backends/backend.go
index 7a00300203b9..34edfae2adf4 100644
--- a/internal/backends/backend.go
+++ b/internal/backends/backend.go
@@ -38,7 +38,7 @@ type Backend interface {
 	ListDatabases(context.Context, *ListDatabasesParams) (*ListDatabasesResult, error)
 	DropDatabase(context.Context, *DropDatabaseParams) error
 
-	Info() *Info
+	Info(context.Context) (*Info, error)
 
 	prometheus.Collector
 
@@ -49,7 +49,7 @@ type Backend interface {
 // Info represents information about a backend.
 type Info struct {
 	Name    string
-	Version string
+	Version string // can be empty if the pool is not initialized yet
 }
 
 // backendContract implements Backend interface.
@@ -141,8 +141,8 @@ func (bc *backendContract) DropDatabase(ctx context.Context, params *DropDatabas
 }
 
 // Info returns information about the backend.
-func (bc *backendContract) Info() *Info {
-	return bc.b.Info()
+func (bc *backendContract) Info(ctx context.Context) (*Info, error) {
+	return bc.b.Info(ctx)
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/backends/postgresql/backend.go b/internal/backends/postgresql/backend.go
index c1369b5d77e4..3d5305a6f22e 100644
--- a/internal/backends/postgresql/backend.go
+++ b/internal/backends/postgresql/backend.go
@@ -24,24 +24,19 @@ import (
 )
 
 // backend implements backends.Backend interface.
-type backend struct {
-	version string
-}
+type backend struct{}
 
 // NewBackendParams represents the parameters of NewBackend function.
 //
 //nolint:vet // for readability
 type NewBackendParams struct {
-	URI     string
-	L       *zap.Logger
-	Version string
+	URI string
+	L   *zap.Logger
 }
 
 // NewBackend creates a new backend for PostgreSQL-compatible database.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	return backends.BackendContract(&backend{
-		version: params.Version,
-	}), nil
+	return backends.BackendContract(&backend{}), nil
 }
 
 // Close implements backends.Backend interface.
@@ -66,7 +61,7 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 }
 
 // Info implements backends.Backend interface.
-func (b *backend) Info() *backends.Info {
+func (b *backend) Info(ctx context.Context) (*backends.Info, error) {
 	panic("not implemented")
 }
 
diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index 6481dfa6c23d..71ba38299e44 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -22,12 +22,12 @@ import (
 
 	"github.com/FerretDB/FerretDB/internal/backends"
 	"github.com/FerretDB/FerretDB/internal/backends/sqlite/metadata"
+	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
 )
 
 // backend implements backends.Backend interface.
 type backend struct {
-	r       *metadata.Registry
-	version string
+	r *metadata.Registry
 }
 
 // NewBackendParams represents the parameters of NewBackend function.
@@ -40,14 +40,13 @@ type NewBackendParams struct {
 
 // NewBackend creates a new SQLite backend.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	r, version, err := metadata.NewRegistry(params.URI, params.L)
+	r, err := metadata.NewRegistry(params.URI, params.L)
 	if err != nil {
 		return nil, err
 	}
 
 	return backends.BackendContract(&backend{
-		r:       r,
-		version: version,
+		r: r,
 	}), nil
 }
 
@@ -87,11 +86,16 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 }
 
 // Info implements backends.Backend interface.
-func (b *backend) Info() *backends.Info {
+func (b *backend) Info(ctx context.Context) (*backends.Info, error) {
+	version, err := b.r.Version(ctx)
+	if err != nil {
+		return nil, lazyerrors.Error(err)
+	}
+
 	return &backends.Info{
 		Name:    "SQLite",
-		Version: b.version,
-	}
+		Version: version,
+	}, nil
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/backends/sqlite/metadata/pool/pool.go b/internal/backends/sqlite/metadata/pool/pool.go
index e6ece43f3192..4a45cb13ee97 100644
--- a/internal/backends/sqlite/metadata/pool/pool.go
+++ b/internal/backends/sqlite/metadata/pool/pool.go
@@ -213,6 +213,23 @@ func (p *Pool) GetExisting(ctx context.Context, name string) *fsql.DB {
 	return db
 }
 
+// GetFirst returns a database from the pool, or nil if there are no databases in the pool.
+//
+// As the pool is not ordered, the returned database is not guaranteed to be the same.
+// This method can be used when a DB-agnostic query is needed.
+func (p *Pool) GetFirst(ctx context.Context) *fsql.DB {
+	defer observability.FuncCall(ctx)()
+
+	p.rw.RLock()
+	defer p.rw.RUnlock()
+
+	for _, db := range p.dbs {
+		return db
+	}
+
+	return nil
+}
+
 // GetOrCreate returns an existing database by valid name, or creates a new one.
 //
 // Returned boolean value indicates whether the database was created.
diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 802610fec987..18124666fc58 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -65,12 +65,10 @@ type Registry struct {
 }
 
 // NewRegistry creates a registry for SQLite databases in the directory specified by SQLite URI.
-//
-// As the second return value, it returns the version of SQLite.
-func NewRegistry(u string, l *zap.Logger) (*Registry, string, error) {
+func NewRegistry(u string, l *zap.Logger) (*Registry, error) {
 	p, initDBs, err := pool.New(u, l)
 	if err != nil {
-		return nil, "", err
+		return nil, err
 	}
 
 	r := &Registry{
@@ -79,35 +77,14 @@ func NewRegistry(u string, l *zap.Logger) (*Registry, string, error) {
 		colls: map[string]map[string]*Collection{},
 	}
 
-	var ver string
 	for name, db := range initDBs {
 		if err = r.initCollections(context.Background(), name, db); err != nil {
 			r.Close()
-			return nil, "", lazyerrors.Error(err)
-		}
-
-		// query version for the first DB only
-		if ver == "" {
-			if ver, err = version(db); err != nil {
-				r.Close()
-				return nil, "", lazyerrors.Error(err)
-			}
+			return nil, lazyerrors.Error(err)
 		}
 	}
 
-	return r, ver, nil
-}
-
-// version returns SQLite version.
-func version(db *fsql.DB) (string, error) {
-	row := db.QueryRowContext(context.Background(), "SELECT sqlite_version()")
-
-	var version string
-	if err := row.Scan(&version); err != nil {
-		return "", lazyerrors.Error(err)
-	}
-
-	return version, nil
+	return r, nil
 }
 
 // Close closes the registry.
@@ -375,6 +352,20 @@ func (r *Registry) CollectionRename(ctx context.Context, dbName, oldCollectionNa
 	panic("not implemented")
 }
 
+// Version returns SQLite version.
+//
+// If there are no databases in the registry, empty string is returned.
+func (r *Registry) Version(ctx context.Context) (string, error) {
+	row := r.p.GetFirst(ctx).QueryRowContext(context.Background(), "SELECT sqlite_version()")
+
+	var version string
+	if err := row.Scan(&version); err != nil {
+		return "", lazyerrors.Error(err)
+	}
+
+	return version, nil
+}
+
 // Describe implements prometheus.Collector.
 func (r *Registry) Describe(ch chan<- *prometheus.Desc) {
 	prometheus.DescribeByCollect(r, ch)
diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index 856e1cbb2de4..dc5ac4a3739d 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -71,10 +71,8 @@ func TestCreateDrop(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
-	r, version, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
+	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
 	require.NoError(t, err)
-	require.Equal(t, "3.35.5", version)
-
 	t.Cleanup(r.Close)
 
 	dbName := t.Name()
@@ -102,7 +100,7 @@ func TestCreateDropStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, _, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -141,7 +139,7 @@ func TestCreateSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, _, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -205,7 +203,7 @@ func TestDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, _, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -254,7 +252,7 @@ func TestCreateDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, _, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t))
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index abcd0495623d..247093612d19 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -87,7 +87,11 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 		state := h.StateProvider.Get()
 
 		info := version.Get()
-		backend := h.b.Info()
+
+		backend, err := h.b.Info(ctx)
+		if err != nil {
+			return nil, lazyerrors.Error(err)
+		}
 
 		startupWarnings := []string{
 			fmt.Sprintf("Powered by FerretDB %s and %s %s.", info.Version, backend.Name, backend.Version),

From 2e085613ff4c1a959a2cf78241f9ccf06aa2d650 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 16:01:06 +0200
Subject: [PATCH 07/22] wip

---
 internal/backends/postgresql/backend.go | 2 +-
 internal/handlers/registry/newpg.go     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/internal/backends/postgresql/backend.go b/internal/backends/postgresql/backend.go
index 3d5305a6f22e..14b38e2bd134 100644
--- a/internal/backends/postgresql/backend.go
+++ b/internal/backends/postgresql/backend.go
@@ -36,7 +36,7 @@ type NewBackendParams struct {
 
 // NewBackend creates a new backend for PostgreSQL-compatible database.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	return backends.BackendContract(&backend{}), nil
+	return backends.BackendContract(new(backend)), nil
 }
 
 // Close implements backends.Backend interface.
diff --git a/internal/handlers/registry/newpg.go b/internal/handlers/registry/newpg.go
index b6e3f5feaf97..31b470c2c1d3 100644
--- a/internal/handlers/registry/newpg.go
+++ b/internal/handlers/registry/newpg.go
@@ -27,7 +27,7 @@ func init() {
 		opts.Logger.Warn("New PostgreSQL backend is in alpha.")
 
 		handlerOpts := &sqlite.NewOpts{
-			Backend: sqlite.PostgreSQL,
+			Backend: "postgresql",
 			URI:     opts.PostgreSQLURL,
 
 			L:             opts.Logger.Named("postgresql"),

From 2f87c9f2776aaffa223dc85e8f703d99d33daf71 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 16:12:06 +0200
Subject: [PATCH 08/22] wip

---
 internal/handlers/pg/pgdb/pool.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/internal/handlers/pg/pgdb/pool.go b/internal/handlers/pg/pgdb/pool.go
index 1dfa66153ebd..07e26d01f17a 100644
--- a/internal/handlers/pg/pgdb/pool.go
+++ b/internal/handlers/pg/pgdb/pool.go
@@ -69,6 +69,9 @@ func NewPool(ctx context.Context, uri string, logger *zap.Logger, p *state.Provi
 			return lazyerrors.Error(err)
 		}
 
+		// After moving pg to the new architecture, we should stop storing the version in the state,
+		// but use backend.Info instead.
+		// TODO https://github.com/FerretDB/FerretDB/issues/3228
 		if err := p.Update(func(s *state.State) { s.HandlerVersion = v }); err != nil {
 			logger.Error("pgdb.Pool.AfterConnect: failed to update state", zap.Error(err))
 		}

From dfadf3c9e49c7a937be7150ea24a73373d361b8f Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 16:14:57 +0200
Subject: [PATCH 09/22] wip

---
 internal/handlers/sqlite/msg_getlog.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 247093612d19..93faa9e48448 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -93,8 +93,12 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 			return nil, lazyerrors.Error(err)
 		}
 
+		if backend.Version != "" {
+			backend.Version = " " + backend.Version // to format startup warnings
+		}
+
 		startupWarnings := []string{
-			fmt.Sprintf("Powered by FerretDB %s and %s %s.", info.Version, backend.Name, backend.Version),
+			fmt.Sprintf("Powered by FerretDB %s and %s%s.", info.Version, backend.Name, backend.Version),
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 

From ae36e38d9489fea480c4367c987d7fff0cc9f2a8 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Wed, 30 Aug 2023 16:18:38 +0200
Subject: [PATCH 10/22] wip

---
 internal/backends/sqlite/metadata/registry.go | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 18124666fc58..03c0830bca2d 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -55,6 +55,8 @@ type Registry struct {
 	p *pool.Pool
 	l *zap.Logger
 
+	version string // SQLite version
+
 	// rw protects colls but also acts like a global lock for the whole registry.
 	// The latter effectively replaces transactions (see the sqlite backend description for more info).
 	// One global lock should be replaced by more granular locks – one per database or even one per collection.
@@ -356,14 +358,17 @@ func (r *Registry) CollectionRename(ctx context.Context, dbName, oldCollectionNa
 //
 // If there are no databases in the registry, empty string is returned.
 func (r *Registry) Version(ctx context.Context) (string, error) {
+	if r.version != "" {
+		return r.version, nil
+	}
+
 	row := r.p.GetFirst(ctx).QueryRowContext(context.Background(), "SELECT sqlite_version()")
 
-	var version string
-	if err := row.Scan(&version); err != nil {
+	if err := row.Scan(&r.version); err != nil {
 		return "", lazyerrors.Error(err)
 	}
 
-	return version, nil
+	return r.version, nil
 }
 
 // Describe implements prometheus.Collector.

From 66cdd3964e082c5a26d7bfe310af0576392d1302 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Thu, 31 Aug 2023 08:06:50 +0200
Subject: [PATCH 11/22] wip

---
 internal/backends/sqlite/metadata/registry.go |  1 -
 .../backends/sqlite/metadata/registry_test.go | 25 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 03c0830bca2d..899529ae1d57 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -363,7 +363,6 @@ func (r *Registry) Version(ctx context.Context) (string, error) {
 	}
 
 	row := r.p.GetFirst(ctx).QueryRowContext(context.Background(), "SELECT sqlite_version()")
-
 	if err := row.Scan(&r.version); err != nil {
 		return "", lazyerrors.Error(err)
 	}
diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index dc5ac4a3739d..99b90296ea35 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -20,6 +20,7 @@ import (
 	"sync/atomic"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/FerretDB/FerretDB/internal/util/fsql"
@@ -297,3 +298,27 @@ func TestCreateDropSameStress(t *testing.T) {
 		})
 	}
 }
+
+func TestVersion(t *testing.T) {
+	t.Parallel()
+	ctx := testutil.Ctx(t)
+
+	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
+	require.NoError(t, err)
+	t.Cleanup(r.Close)
+
+	dbName := t.Name()
+
+	// database must exist, so version can be queried
+	db, err := r.DatabaseGetOrCreate(ctx, dbName)
+	require.NoError(t, err)
+	require.NotNil(t, db)
+
+	t.Cleanup(func() {
+		r.DatabaseDrop(ctx, dbName)
+	})
+
+	version, err := r.Version(ctx)
+	require.NoError(t, err)
+	assert.Equal(t, "3.41.2", version)
+}

From 12da6332ca9f6e52ea7d419e2cf4d19344dbb24c Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Thu, 31 Aug 2023 08:28:27 +0200
Subject: [PATCH 12/22] wip

---
 internal/backends/sqlite/metadata/registry_test.go | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index 98cab3a635ab..0bf86f5d46ec 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -309,7 +309,12 @@ func TestVersion(t *testing.T) {
 
 	dbName := t.Name()
 
-	// database must exist, so version can be queried
+	// trying to get the version while database does not exist
+	version, err := r.Version(ctx)
+	require.NoError(t, err)
+	assert.Equal(t, "", version)
+
+	// database exists, so version can be queried
 	db, err := r.DatabaseGetOrCreate(ctx, dbName)
 	require.NoError(t, err)
 	require.NotNil(t, db)
@@ -318,7 +323,7 @@ func TestVersion(t *testing.T) {
 		r.DatabaseDrop(ctx, dbName)
 	})
 
-	version, err := r.Version(ctx)
+	version, err = r.Version(ctx)
 	require.NoError(t, err)
 	assert.Equal(t, "3.41.2", version)
 }

From 76b8d996fbc616fd6c969e2c5e2a5a0868651bf1 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Thu, 31 Aug 2023 08:29:27 +0200
Subject: [PATCH 13/22] wip

---
 internal/backends/sqlite/metadata/registry.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 899529ae1d57..dcde452af7bf 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -362,7 +362,12 @@ func (r *Registry) Version(ctx context.Context) (string, error) {
 		return r.version, nil
 	}
 
-	row := r.p.GetFirst(ctx).QueryRowContext(context.Background(), "SELECT sqlite_version()")
+	db := r.p.GetFirst(ctx)
+	if db == nil {
+		return "", nil
+	}
+
+	row := db.QueryRowContext(context.Background(), "SELECT sqlite_version()")
 	if err := row.Scan(&r.version); err != nil {
 		return "", lazyerrors.Error(err)
 	}

From 75b5cdddbef1d5241c6f7ef3a27900caf0cd3568 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Thu, 31 Aug 2023 08:45:34 +0200
Subject: [PATCH 14/22] wip

---
 internal/backends/sqlite/metadata/registry_test.go | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index 0bf86f5d46ec..b5ab7ca81a49 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -319,9 +319,12 @@ func TestVersion(t *testing.T) {
 	require.NoError(t, err)
 	require.NotNil(t, db)
 
-	t.Cleanup(func() {
-		r.DatabaseDrop(ctx, dbName)
-	})
+	version, err = r.Version(ctx)
+	require.NoError(t, err)
+	assert.Equal(t, "3.41.2", version)
+
+	// no databases available, but the version should be returned because it's stored in the registry
+	r.DatabaseDrop(ctx, dbName)
 
 	version, err = r.Version(ctx)
 	require.NoError(t, err)

From e48a0bb94f4028e31588e4ce7c43bc901bc73a39 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Thu, 31 Aug 2023 09:20:12 +0200
Subject: [PATCH 15/22] wip

---
 internal/backends/sqlite/metadata/registry.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index dcde452af7bf..659b693f8aa2 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -367,7 +367,7 @@ func (r *Registry) Version(ctx context.Context) (string, error) {
 		return "", nil
 	}
 
-	row := db.QueryRowContext(context.Background(), "SELECT sqlite_version()")
+	row := db.QueryRowContext(ctx, "SELECT sqlite_version()")
 	if err := row.Scan(&r.version); err != nil {
 		return "", lazyerrors.Error(err)
 	}

From cee30ac2d0adbc385a4c0d3d16f18a4ea668450b Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 13:42:43 +0200
Subject: [PATCH 16/22] use state

---
 internal/backends/sqlite/backend.go           |  4 ++-
 .../backends/sqlite/metadata/pool/pool.go     | 25 ++++++++++++---
 .../sqlite/metadata/pool/pool_test.go         | 16 ++++++++--
 internal/backends/sqlite/metadata/registry.go |  5 +--
 .../backends/sqlite/metadata/registry_test.go | 31 +++++++++++++++----
 internal/handlers/pg/pgdb/pool.go             |  3 --
 6 files changed, 65 insertions(+), 19 deletions(-)

diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index 71ba38299e44..e97a11266d74 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -23,6 +23,7 @@ import (
 	"github.com/FerretDB/FerretDB/internal/backends"
 	"github.com/FerretDB/FerretDB/internal/backends/sqlite/metadata"
 	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
+	"github.com/FerretDB/FerretDB/internal/util/state"
 )
 
 // backend implements backends.Backend interface.
@@ -36,11 +37,12 @@ type backend struct {
 type NewBackendParams struct {
 	URI string
 	L   *zap.Logger
+	P   *state.Provider
 }
 
 // NewBackend creates a new SQLite backend.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
-	r, err := metadata.NewRegistry(params.URI, params.L)
+	r, err := metadata.NewRegistry(params.URI, params.L, params.P)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/backends/sqlite/metadata/pool/pool.go b/internal/backends/sqlite/metadata/pool/pool.go
index 4a45cb13ee97..639da6cec4e2 100644
--- a/internal/backends/sqlite/metadata/pool/pool.go
+++ b/internal/backends/sqlite/metadata/pool/pool.go
@@ -38,6 +38,7 @@ import (
 	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
 	"github.com/FerretDB/FerretDB/internal/util/observability"
 	"github.com/FerretDB/FerretDB/internal/util/resource"
+	"github.com/FerretDB/FerretDB/internal/util/state"
 )
 
 // filenameExtension represents SQLite database filename extension.
@@ -60,6 +61,8 @@ type Pool struct {
 	dbs map[string]*fsql.DB
 
 	token *resource.Token
+
+	sp *state.Provider
 }
 
 // openDB opens existing database or creates a new one.
@@ -68,7 +71,7 @@ type Pool struct {
 // so no validation is needed.
 // One exception is very long full path names for the filesystem,
 // but we don't check it.
-func openDB(name, uri string, singleConn bool, l *zap.Logger) (*fsql.DB, error) {
+func openDB(name, uri string, singleConn bool, l *zap.Logger, sp *state.Provider) (*fsql.DB, error) {
 	db, err := sql.Open("sqlite", uri)
 	if err != nil {
 		return nil, lazyerrors.Error(err)
@@ -88,6 +91,19 @@ func openDB(name, uri string, singleConn bool, l *zap.Logger) (*fsql.DB, error)
 		return nil, lazyerrors.Error(err)
 	}
 
+	if err := sp.Update(func(s *state.State) {
+		if s.HandlerVersion != "" {
+			return
+		}
+
+		row := db.QueryRowContext(context.Background(), "SELECT sqlite_version()")
+		if err := row.Scan(&s.HandlerVersion); err != nil {
+			l.Error("sqlite.metadata.pool.openDB: failed to query SQLite version", zap.Error(err))
+		}
+	}); err != nil {
+		l.Error("sqlite.metadata.pool.openDB: failed to update state", zap.Error(err))
+	}
+
 	return fsql.WrapDB(db, name, l), nil
 }
 
@@ -97,7 +113,7 @@ func openDB(name, uri string, singleConn bool, l *zap.Logger) (*fsql.DB, error)
 //
 // The returned map is the initial set of existing databases.
 // It should not be modified.
-func New(u string, l *zap.Logger) (*Pool, map[string]*fsql.DB, error) {
+func New(u string, l *zap.Logger, sp *state.Provider) (*Pool, map[string]*fsql.DB, error) {
 	uri, err := parseURI(u)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to parse SQLite URI %q: %s", u, err)
@@ -113,6 +129,7 @@ func New(u string, l *zap.Logger) (*Pool, map[string]*fsql.DB, error) {
 		l:     l,
 		dbs:   make(map[string]*fsql.DB, len(matches)),
 		token: resource.NewToken(),
+		sp:    sp,
 	}
 
 	resource.Track(p, p.token)
@@ -123,7 +140,7 @@ func New(u string, l *zap.Logger) (*Pool, map[string]*fsql.DB, error) {
 
 		p.l.Debug("Opening existing database.", zap.String("name", name), zap.String("uri", uri))
 
-		db, err := openDB(name, uri, p.singleConn(), l)
+		db, err := openDB(name, uri, p.singleConn(), l, p.sp)
 		if err != nil {
 			p.Close()
 			return nil, nil, lazyerrors.Error(err)
@@ -250,7 +267,7 @@ func (p *Pool) GetOrCreate(ctx context.Context, name string) (*fsql.DB, bool, er
 	}
 
 	uri := p.databaseURI(name)
-	db, err := openDB(name, uri, p.singleConn(), p.l)
+	db, err := openDB(name, uri, p.singleConn(), p.l, p.sp)
 	if err != nil {
 		return nil, false, lazyerrors.Errorf("%s: %w", uri, err)
 	}
diff --git a/internal/backends/sqlite/metadata/pool/pool_test.go b/internal/backends/sqlite/metadata/pool/pool_test.go
index 0ff253b61389..cb725716b30b 100644
--- a/internal/backends/sqlite/metadata/pool/pool_test.go
+++ b/internal/backends/sqlite/metadata/pool/pool_test.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/FerretDB/FerretDB/internal/util/state"
 	"github.com/FerretDB/FerretDB/internal/util/testutil"
 	"github.com/FerretDB/FerretDB/internal/util/testutil/teststress"
 )
@@ -29,8 +30,11 @@ func TestCreateDrop(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	// that also tests that query parameters are preserved by using non-writable directory
-	p, _, err := New("file:/?mode=memory&_pragma=journal_mode(wal)", testutil.Logger(t))
+	p, _, err := New("file:/?mode=memory&_pragma=journal_mode(wal)", testutil.Logger(t), sp)
 	require.NoError(t, err)
 	t.Cleanup(p.Close)
 
@@ -76,6 +80,9 @@ func TestCreateDrop(t *testing.T) {
 func TestCreateDropStress(t *testing.T) {
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	for testName, uri := range map[string]string{
 		"file":             "file:./",
 		"file-immediate":   "file:./?_txlock=immediate",
@@ -83,7 +90,7 @@ func TestCreateDropStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			p, _, err := New(uri, testutil.Logger(t))
+			p, _, err := New(uri, testutil.Logger(t), sp)
 			require.NoError(t, err)
 			t.Cleanup(p.Close)
 
@@ -137,7 +144,10 @@ func TestDefaults(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
-	p, _, err := New("file:./", testutil.Logger(t))
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
+	p, _, err := New("file:./", testutil.Logger(t), sp)
 	require.NoError(t, err)
 
 	dbName := testutil.DatabaseName(t)
diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 659b693f8aa2..53397487a2d0 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -31,6 +31,7 @@ import (
 	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
 	"github.com/FerretDB/FerretDB/internal/util/must"
 	"github.com/FerretDB/FerretDB/internal/util/observability"
+	"github.com/FerretDB/FerretDB/internal/util/state"
 )
 
 const (
@@ -67,8 +68,8 @@ type Registry struct {
 }
 
 // NewRegistry creates a registry for SQLite databases in the directory specified by SQLite URI.
-func NewRegistry(u string, l *zap.Logger) (*Registry, error) {
-	p, initDBs, err := pool.New(u, l)
+func NewRegistry(u string, l *zap.Logger, sp *state.Provider) (*Registry, error) {
+	p, initDBs, err := pool.New(u, l, sp)
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index b5ab7ca81a49..d4ab8b5e3cb6 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -24,6 +24,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/FerretDB/FerretDB/internal/util/fsql"
+	"github.com/FerretDB/FerretDB/internal/util/state"
 	"github.com/FerretDB/FerretDB/internal/util/testutil"
 	"github.com/FerretDB/FerretDB/internal/util/testutil/teststress"
 )
@@ -72,7 +73,10 @@ func TestCreateDrop(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
-	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
+	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t), sp)
 	require.NoError(t, err)
 	t.Cleanup(r.Close)
 
@@ -94,6 +98,9 @@ func TestCreateDrop(t *testing.T) {
 func TestCreateDropStress(t *testing.T) {
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	for testName, uri := range map[string]string{
 		"file":             "file:./",
 		"file-immediate":   "file:./?_txlock=immediate",
@@ -101,7 +108,7 @@ func TestCreateDropStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t), sp)
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -133,6 +140,9 @@ func TestCreateDropStress(t *testing.T) {
 func TestCreateSameStress(t *testing.T) {
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	for testName, uri := range map[string]string{
 		"file":             "file:./",
 		"file-immediate":   "file:./?_txlock=immediate",
@@ -140,7 +150,7 @@ func TestCreateSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t), sp)
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -197,6 +207,9 @@ func TestCreateSameStress(t *testing.T) {
 func TestDropSameStress(t *testing.T) {
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	for testName, uri := range map[string]string{
 		"file":             "file:./",
 		"file-immediate":   "file:./?_txlock=immediate",
@@ -204,7 +217,7 @@ func TestDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t), sp)
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -246,6 +259,9 @@ func TestDropSameStress(t *testing.T) {
 func TestCreateDropSameStress(t *testing.T) {
 	ctx := testutil.Ctx(t)
 
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
 	for testName, uri := range map[string]string{
 		"file":             "file:./",
 		"file-immediate":   "file:./?_txlock=immediate",
@@ -253,7 +269,7 @@ func TestCreateDropSameStress(t *testing.T) {
 		"memory-immediate": "file:./?mode=memory&_txlock=immediate",
 	} {
 		t.Run(testName, func(t *testing.T) {
-			r, err := NewRegistry(uri, testutil.Logger(t))
+			r, err := NewRegistry(uri, testutil.Logger(t), sp)
 			require.NoError(t, err)
 			t.Cleanup(r.Close)
 
@@ -303,7 +319,10 @@ func TestVersion(t *testing.T) {
 	t.Parallel()
 	ctx := testutil.Ctx(t)
 
-	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t))
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
+	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t), sp)
 	require.NoError(t, err)
 	t.Cleanup(r.Close)
 
diff --git a/internal/handlers/pg/pgdb/pool.go b/internal/handlers/pg/pgdb/pool.go
index 07e26d01f17a..1dfa66153ebd 100644
--- a/internal/handlers/pg/pgdb/pool.go
+++ b/internal/handlers/pg/pgdb/pool.go
@@ -69,9 +69,6 @@ func NewPool(ctx context.Context, uri string, logger *zap.Logger, p *state.Provi
 			return lazyerrors.Error(err)
 		}
 
-		// After moving pg to the new architecture, we should stop storing the version in the state,
-		// but use backend.Info instead.
-		// TODO https://github.com/FerretDB/FerretDB/issues/3228
 		if err := p.Update(func(s *state.State) { s.HandlerVersion = v }); err != nil {
 			logger.Error("pgdb.Pool.AfterConnect: failed to update state", zap.Error(err))
 		}

From 14b585385774814804217decb4b760f7a99c53b9 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 13:46:21 +0200
Subject: [PATCH 17/22] print version

---
 internal/handlers/sqlite/msg_getlog.go | 13 ++++++++-----
 internal/handlers/sqlite/sqlite.go     |  1 +
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 93faa9e48448..9f656ee231f7 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -18,6 +18,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"strings"
 	"time"
 
 	"go.uber.org/zap"
@@ -88,17 +89,19 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 
 		info := version.Get()
 
+		// it may be empty if no connection was established yet
+		hv, _, _ := strings.Cut(state.HandlerVersion, " ")
+		if hv != "" {
+			hv = " " + hv
+		}
+
 		backend, err := h.b.Info(ctx)
 		if err != nil {
 			return nil, lazyerrors.Error(err)
 		}
 
-		if backend.Version != "" {
-			backend.Version = " " + backend.Version // to format startup warnings
-		}
-
 		startupWarnings := []string{
-			fmt.Sprintf("Powered by FerretDB %s and %s%s.", info.Version, backend.Name, backend.Version),
+			fmt.Sprintf("Powered by FerretDB %s and %s%s.", info.Version, backend.Name, hv),
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 
diff --git a/internal/handlers/sqlite/sqlite.go b/internal/handlers/sqlite/sqlite.go
index e77a0b3c80bc..6629b6a126f1 100644
--- a/internal/handlers/sqlite/sqlite.go
+++ b/internal/handlers/sqlite/sqlite.go
@@ -81,6 +81,7 @@ func New(opts *NewOpts) (handlers.Interface, error) {
 		b, err = sqlite.NewBackend(&sqlite.NewBackendParams{
 			URI: opts.URI,
 			L:   opts.L,
+			P:   opts.StateProvider,
 		})
 	default:
 		panic("unknown backend: " + opts.Backend)

From 84f7e847eaca481989aceac80317ed2271b11af6 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 13:56:53 +0200
Subject: [PATCH 18/22] remove unnecessary version

---
 internal/backends/backend.go            | 14 ++++----------
 internal/backends/postgresql/backend.go |  6 +++---
 internal/backends/sqlite/backend.go     | 15 +++------------
 internal/handlers/sqlite/msg_getlog.go  |  7 +------
 4 files changed, 11 insertions(+), 31 deletions(-)

diff --git a/internal/backends/backend.go b/internal/backends/backend.go
index 34edfae2adf4..2d6adbc4e382 100644
--- a/internal/backends/backend.go
+++ b/internal/backends/backend.go
@@ -38,7 +38,7 @@ type Backend interface {
 	ListDatabases(context.Context, *ListDatabasesParams) (*ListDatabasesResult, error)
 	DropDatabase(context.Context, *DropDatabaseParams) error
 
-	Info(context.Context) (*Info, error)
+	Name() string
 
 	prometheus.Collector
 
@@ -46,12 +46,6 @@ type Backend interface {
 	// TODO https://github.com/FerretDB/FerretDB/issues/3069
 }
 
-// Info represents information about a backend.
-type Info struct {
-	Name    string
-	Version string // can be empty if the pool is not initialized yet
-}
-
 // backendContract implements Backend interface.
 type backendContract struct {
 	b     Backend
@@ -140,9 +134,9 @@ func (bc *backendContract) DropDatabase(ctx context.Context, params *DropDatabas
 	return err
 }
 
-// Info returns information about the backend.
-func (bc *backendContract) Info(ctx context.Context) (*Info, error) {
-	return bc.b.Info(ctx)
+// Name returns human-readable formatted name of the backend.
+func (bc *backendContract) Name() string {
+	return bc.b.Name()
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/backends/postgresql/backend.go b/internal/backends/postgresql/backend.go
index 14b38e2bd134..8b1a1fcbd2aa 100644
--- a/internal/backends/postgresql/backend.go
+++ b/internal/backends/postgresql/backend.go
@@ -60,9 +60,9 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 	panic("not implemented")
 }
 
-// Info implements backends.Backend interface.
-func (b *backend) Info(ctx context.Context) (*backends.Info, error) {
-	panic("not implemented")
+// Name implements backends.Backend interface.
+func (b *backend) Name() string {
+	return "PostgreSQL"
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index e97a11266d74..ea0aa249df07 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -22,7 +22,6 @@ import (
 
 	"github.com/FerretDB/FerretDB/internal/backends"
 	"github.com/FerretDB/FerretDB/internal/backends/sqlite/metadata"
-	"github.com/FerretDB/FerretDB/internal/util/lazyerrors"
 	"github.com/FerretDB/FerretDB/internal/util/state"
 )
 
@@ -87,17 +86,9 @@ func (b *backend) DropDatabase(ctx context.Context, params *backends.DropDatabas
 	return nil
 }
 
-// Info implements backends.Backend interface.
-func (b *backend) Info(ctx context.Context) (*backends.Info, error) {
-	version, err := b.r.Version(ctx)
-	if err != nil {
-		return nil, lazyerrors.Error(err)
-	}
-
-	return &backends.Info{
-		Name:    "SQLite",
-		Version: version,
-	}, nil
+// Name implements backends.Backend interface.
+func (b *backend) Name() string {
+	return "SQLite"
 }
 
 // Describe implements prometheus.Collector.
diff --git a/internal/handlers/sqlite/msg_getlog.go b/internal/handlers/sqlite/msg_getlog.go
index 9f656ee231f7..d1d27c39e4c5 100644
--- a/internal/handlers/sqlite/msg_getlog.go
+++ b/internal/handlers/sqlite/msg_getlog.go
@@ -95,13 +95,8 @@ func (h *Handler) MsgGetLog(ctx context.Context, msg *wire.OpMsg) (*wire.OpMsg,
 			hv = " " + hv
 		}
 
-		backend, err := h.b.Info(ctx)
-		if err != nil {
-			return nil, lazyerrors.Error(err)
-		}
-
 		startupWarnings := []string{
-			fmt.Sprintf("Powered by FerretDB %s and %s%s.", info.Version, backend.Name, hv),
+			fmt.Sprintf("Powered by FerretDB %s and %s%s.", info.Version, h.b.Name(), hv),
 			"Please star us on GitHub: https://github.com/FerretDB/FerretDB.",
 		}
 

From badab62617151dac254d3b1522a69e97c6fa4c5e Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 14:13:59 +0200
Subject: [PATCH 19/22] cleanup version calculation

---
 .../backends/sqlite/metadata/pool/pool.go     | 17 ---------
 internal/backends/sqlite/metadata/registry.go | 23 ------------
 .../backends/sqlite/metadata/registry_test.go | 36 -------------------
 3 files changed, 76 deletions(-)

diff --git a/internal/backends/sqlite/metadata/pool/pool.go b/internal/backends/sqlite/metadata/pool/pool.go
index 639da6cec4e2..2d078121fd66 100644
--- a/internal/backends/sqlite/metadata/pool/pool.go
+++ b/internal/backends/sqlite/metadata/pool/pool.go
@@ -230,23 +230,6 @@ func (p *Pool) GetExisting(ctx context.Context, name string) *fsql.DB {
 	return db
 }
 
-// GetFirst returns a database from the pool, or nil if there are no databases in the pool.
-//
-// As the pool is not ordered, the returned database is not guaranteed to be the same.
-// This method can be used when a DB-agnostic query is needed.
-func (p *Pool) GetFirst(ctx context.Context) *fsql.DB {
-	defer observability.FuncCall(ctx)()
-
-	p.rw.RLock()
-	defer p.rw.RUnlock()
-
-	for _, db := range p.dbs {
-		return db
-	}
-
-	return nil
-}
-
 // GetOrCreate returns an existing database by valid name, or creates a new one.
 //
 // Returned boolean value indicates whether the database was created.
diff --git a/internal/backends/sqlite/metadata/registry.go b/internal/backends/sqlite/metadata/registry.go
index 53397487a2d0..155eb8a75825 100644
--- a/internal/backends/sqlite/metadata/registry.go
+++ b/internal/backends/sqlite/metadata/registry.go
@@ -56,8 +56,6 @@ type Registry struct {
 	p *pool.Pool
 	l *zap.Logger
 
-	version string // SQLite version
-
 	// rw protects colls but also acts like a global lock for the whole registry.
 	// The latter effectively replaces transactions (see the sqlite backend description for more info).
 	// One global lock should be replaced by more granular locks – one per database or even one per collection.
@@ -355,27 +353,6 @@ func (r *Registry) CollectionRename(ctx context.Context, dbName, oldCollectionNa
 	panic("not implemented")
 }
 
-// Version returns SQLite version.
-//
-// If there are no databases in the registry, empty string is returned.
-func (r *Registry) Version(ctx context.Context) (string, error) {
-	if r.version != "" {
-		return r.version, nil
-	}
-
-	db := r.p.GetFirst(ctx)
-	if db == nil {
-		return "", nil
-	}
-
-	row := db.QueryRowContext(ctx, "SELECT sqlite_version()")
-	if err := row.Scan(&r.version); err != nil {
-		return "", lazyerrors.Error(err)
-	}
-
-	return r.version, nil
-}
-
 // Describe implements prometheus.Collector.
 func (r *Registry) Describe(ch chan<- *prometheus.Desc) {
 	prometheus.DescribeByCollect(r, ch)
diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index d4ab8b5e3cb6..c6f210a6e122 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -20,7 +20,6 @@ import (
 	"sync/atomic"
 	"testing"
 
-	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/FerretDB/FerretDB/internal/util/fsql"
@@ -314,38 +313,3 @@ func TestCreateDropSameStress(t *testing.T) {
 		})
 	}
 }
-
-func TestVersion(t *testing.T) {
-	t.Parallel()
-	ctx := testutil.Ctx(t)
-
-	sp, err := state.NewProvider("")
-	require.NoError(t, err)
-
-	r, err := NewRegistry("file:./?mode=memory", testutil.Logger(t), sp)
-	require.NoError(t, err)
-	t.Cleanup(r.Close)
-
-	dbName := t.Name()
-
-	// trying to get the version while database does not exist
-	version, err := r.Version(ctx)
-	require.NoError(t, err)
-	assert.Equal(t, "", version)
-
-	// database exists, so version can be queried
-	db, err := r.DatabaseGetOrCreate(ctx, dbName)
-	require.NoError(t, err)
-	require.NotNil(t, db)
-
-	version, err = r.Version(ctx)
-	require.NoError(t, err)
-	assert.Equal(t, "3.41.2", version)
-
-	// no databases available, but the version should be returned because it's stored in the registry
-	r.DatabaseDrop(ctx, dbName)
-
-	version, err = r.Version(ctx)
-	require.NoError(t, err)
-	assert.Equal(t, "3.41.2", version)
-}

From 3e27ca3441da08d05e0783377ceaac0d282007f2 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 15:07:13 +0200
Subject: [PATCH 20/22] add test for version

---
 internal/backends/sqlite/metadata/registry_test.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/internal/backends/sqlite/metadata/registry_test.go b/internal/backends/sqlite/metadata/registry_test.go
index 055abfb907ce..e240198fe0a3 100644
--- a/internal/backends/sqlite/metadata/registry_test.go
+++ b/internal/backends/sqlite/metadata/registry_test.go
@@ -85,6 +85,9 @@ func TestCreateDrop(t *testing.T) {
 	require.NoError(t, err)
 	require.NotNil(t, db)
 
+	state := sp.Get()
+	require.Equal(t, "3.41.2", state.HandlerVersion)
+
 	t.Cleanup(func() {
 		r.DatabaseDrop(ctx, dbName)
 	})

From 9c4317defb6c894102d813fad87c632c9b829431 Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 15:43:58 +0200
Subject: [PATCH 21/22] fix tests

---
 internal/backends/postgresql/collection.go  | 2 +-
 internal/backends/sqlite/collection.go      | 2 +-
 internal/backends/sqlite/collection_test.go | 6 +++++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/internal/backends/postgresql/collection.go b/internal/backends/postgresql/collection.go
index 046574065777..412e92d269dc 100644
--- a/internal/backends/postgresql/collection.go
+++ b/internal/backends/postgresql/collection.go
@@ -39,7 +39,7 @@ func (c *collection) Query(ctx context.Context, params *backends.QueryParams) (*
 	panic("not implemented")
 }
 
-// Insert implements backends.Collection interface.
+// InsertAll implements backends.Collection interface.
 func (c *collection) InsertAll(ctx context.Context, params *backends.InsertAllParams) (*backends.InsertAllResult, error) {
 	panic("not implemented")
 }
diff --git a/internal/backends/sqlite/collection.go b/internal/backends/sqlite/collection.go
index 02c7a1bfb1be..f2d1a7d6206e 100644
--- a/internal/backends/sqlite/collection.go
+++ b/internal/backends/sqlite/collection.go
@@ -75,7 +75,7 @@ func (c *collection) Query(ctx context.Context, params *backends.QueryParams) (*
 	}, nil
 }
 
-// Insert implements backends.Collection interface.
+// InsertAll implements backends.Collection interface.
 func (c *collection) InsertAll(ctx context.Context, params *backends.InsertAllParams) (*backends.InsertAllResult, error) {
 	if _, err := c.r.CollectionCreate(ctx, c.dbName, c.name); err != nil {
 		return nil, lazyerrors.Error(err)
diff --git a/internal/backends/sqlite/collection_test.go b/internal/backends/sqlite/collection_test.go
index 2bef278cd7e9..b6fd0161c1b1 100644
--- a/internal/backends/sqlite/collection_test.go
+++ b/internal/backends/sqlite/collection_test.go
@@ -21,11 +21,15 @@ import (
 
 	"github.com/FerretDB/FerretDB/internal/backends"
 	"github.com/FerretDB/FerretDB/internal/types"
+	"github.com/FerretDB/FerretDB/internal/util/state"
 	"github.com/FerretDB/FerretDB/internal/util/testutil"
 )
 
 func TestInsert(t *testing.T) {
-	b, err := NewBackend(&NewBackendParams{URI: "file:./?mode=memory", L: testutil.Logger(t)})
+	sp, err := state.NewProvider("")
+	require.NoError(t, err)
+
+	b, err := NewBackend(&NewBackendParams{URI: "file:./?mode=memory", L: testutil.Logger(t), P: sp})
 	require.NoError(t, err)
 
 	defer b.Close()

From 83a834b9ec88e62c3b36b6718ce37d3033ed745e Mon Sep 17 00:00:00 2001
From: Elena Grahovac <elena@grahovac.me>
Date: Fri, 1 Sep 2023 15:47:20 +0200
Subject: [PATCH 22/22] wip

---
 internal/backends/sqlite/backend.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/internal/backends/sqlite/backend.go b/internal/backends/sqlite/backend.go
index ea0aa249df07..05a93758050e 100644
--- a/internal/backends/sqlite/backend.go
+++ b/internal/backends/sqlite/backend.go
@@ -41,6 +41,10 @@ type NewBackendParams struct {
 
 // NewBackend creates a new SQLite backend.
 func NewBackend(params *NewBackendParams) (backends.Backend, error) {
+	if params.P == nil {
+		panic("state provider is required but not set")
+	}
+
 	r, err := metadata.NewRegistry(params.URI, params.L, params.P)
 	if err != nil {
 		return nil, err