diff --git a/crates/libanalysis/src/db/imp.rs b/crates/libanalysis/src/db/imp.rs
index 1b4ee5cf31..f26be10463 100644
--- a/crates/libanalysis/src/db/imp.rs
+++ b/crates/libanalysis/src/db/imp.rs
@@ -122,9 +122,6 @@ impl QueryRegistry {
         let config = config.with_query(id, q.f());
         self.config= Some(config);
     }
-    pub(super) fn finish(mut self) -> salsa::QueryConfig<State, Data> {
-        self.config.take().unwrap()
-    }
 }
 
 fn hash<T: Hash>(x: &T) -> u64 {
diff --git a/crates/libanalysis/src/db/mod.rs b/crates/libanalysis/src/db/mod.rs
index 1111a4f874..22769d1120 100644
--- a/crates/libanalysis/src/db/mod.rs
+++ b/crates/libanalysis/src/db/mod.rs
@@ -29,6 +29,12 @@ pub(crate) struct QueryRegistry {
     imp: imp::QueryRegistry,
 }
 
+impl Default for Db {
+    fn default() -> Db {
+        Db::new()
+    }
+}
+
 impl Db {
     pub(crate) fn new() -> Db {
         let reg = QueryRegistry::new();
@@ -44,6 +50,7 @@ impl Db {
         let ctx = QueryCtx { imp: &self.imp.imp.query_ctx() };
         f(ctx)
     }
+    #[allow(unused)]
     pub(crate) fn trace_query<F: FnOnce(QueryCtx) -> R, R>(&self, f: F) -> (R, Vec<&'static str>) {
         let ctx = QueryCtx { imp: &self.imp.imp.query_ctx() };
         let res = f(ctx);
@@ -65,42 +72,11 @@ pub(crate) fn file_text(ctx: QueryCtx, file_id: FileId) -> Arc<String> {
 pub(crate) fn file_set(ctx: QueryCtx) -> Arc<(Vec<FileId>, FileResolverImp)> {
     imp::file_set(ctx)
 }
-pub(crate) use self::queries::file_syntax;
-
-mod queries {
-    use std::sync::Arc;
-    use libsyntax2::File;
-    use libeditor::LineIndex;
-    use {FileId};
-    use super::{Query, QueryCtx, QueryRegistry, file_text};
-
-    pub(crate) fn register_queries(reg: &mut QueryRegistry) {
-        reg.add(FILE_SYNTAX, "FILE_SYNTAX");
-        reg.add(FILE_LINES, "FILE_LINES");
-    }
-
-    pub(crate) fn file_syntax(ctx: QueryCtx, file_id: FileId) -> File {
-        (&*ctx.get(FILE_SYNTAX, file_id)).clone()
-    }
-    pub(crate) fn file_lines(ctx: QueryCtx, file_id: FileId) -> Arc<LineIndex> {
-        ctx.get(FILE_LINES, file_id)
-    }
-
-    pub(super) const FILE_SYNTAX: Query<FileId, File> = Query(16, |ctx, file_id: &FileId| {
-        let text = file_text(ctx, *file_id);
-        File::parse(&*text)
-    });
-    pub(super) const FILE_LINES: Query<FileId, LineIndex> = Query(17, |ctx, file_id: &FileId| {
-        let text = file_text(ctx, *file_id);
-        LineIndex::new(&*text)
-    });
-}
-
 impl QueryRegistry {
     fn new() -> QueryRegistry {
         let mut reg = QueryRegistry { imp: imp::QueryRegistry::new() };
-        queries::register_queries(&mut reg);
-        ::module_map_db::register_queries(&mut reg);
+        ::queries::register_queries(&mut reg);
+        ::module_map::register_queries(&mut reg);
         reg
     }
     pub(crate) fn add<Q: imp::EvalQuery>(&mut self, q: Q, name: &'static str) {
diff --git a/crates/libanalysis/src/descriptors.rs b/crates/libanalysis/src/descriptors.rs
index 200f21576b..93a4158e44 100644
--- a/crates/libanalysis/src/descriptors.rs
+++ b/crates/libanalysis/src/descriptors.rs
@@ -140,7 +140,7 @@ impl ModuleTreeDescriptor {
             .links
             .iter()
             .filter(|it| it.name(self) == name)
-            .map(|link| link.owner(self))
+            .flat_map(|link| link.points_to(self).iter().map(|&node| self.node(node).file_id))
             .collect()
     }
     pub(crate) fn problems<'a, 'b>(&'b self, file_id: FileId, root: ast::Root<'a>) -> Vec<(ast::Name<'a>, &'b Problem)> {
@@ -172,6 +172,9 @@ impl Link {
         let owner = tree.link(self).owner;
         tree.node(owner).file_id
     }
+    fn points_to(self, tree: &ModuleTreeDescriptor) -> &[Node] {
+        &tree.link(self).points_to
+    }
     pub(crate) fn bind_source<'a>(self, tree: &ModuleTreeDescriptor, root: ast::Root<'a>) -> ast::Module<'a> {
         modules(root)
             .filter(|(name, _)| name == &tree.link(self).name)
diff --git a/crates/libanalysis/src/imp.rs b/crates/libanalysis/src/imp.rs
index 8734813f49..6f3191fe73 100644
--- a/crates/libanalysis/src/imp.rs
+++ b/crates/libanalysis/src/imp.rs
@@ -5,6 +5,7 @@ use std::{
     },
     fmt,
     collections::{HashSet, VecDeque},
+    iter,
 };
 
 use relative_path::RelativePath;
@@ -75,14 +76,12 @@ impl AnalysisHostImpl {
     }
     pub fn change_files(&mut self, changes: &mut dyn Iterator<Item=(FileId, Option<String>)>) {
         let data = self.data_mut();
-        for (file_id, text) in changes {
-            data.root.update(file_id, text);
-        }
+        data.root = Arc::new(data.root.apply_changes(changes, None));
     }
     pub fn set_file_resolver(&mut self, resolver: FileResolverImp) {
         let data = self.data_mut();
         data.file_resolver = resolver.clone();
-        data.root.set_file_resolver(resolver);
+        data.root = Arc::new(data.root.apply_changes(&mut iter::empty(), Some(resolver)));
     }
     pub fn set_crate_graph(&mut self, graph: CrateGraph) {
         let mut visited = HashSet::new();
@@ -124,18 +123,17 @@ impl Clone for AnalysisImpl {
 impl AnalysisImpl {
     fn root(&self, file_id: FileId) -> &SourceRoot {
         if self.data.root.contains(file_id) {
-            return &self.data.root;
+            return &*self.data.root;
         }
         &**self.data.libs.iter().find(|it| it.contains(file_id)).unwrap()
     }
-    pub fn file_syntax(&self, file_id: FileId) -> &File {
+    pub fn file_syntax(&self, file_id: FileId) -> File {
         self.root(file_id).syntax(file_id)
     }
-    pub fn file_line_index(&self, file_id: FileId) -> &LineIndex {
+    pub fn file_line_index(&self, file_id: FileId) -> Arc<LineIndex> {
         self.root(file_id).lines(file_id)
     }
     pub fn world_symbols(&self, query: Query, token: &JobToken) -> Vec<(FileId, FileSymbol)> {
-        self.reindex();
         let mut buf = Vec::new();
         if query.libs {
             self.data.libs.iter()
@@ -308,19 +306,13 @@ impl AnalysisImpl {
         };
         module_tree.child_module_by_name(file_id, name.as_str())
     }
-
-    fn reindex(&self) {
-        if self.needs_reindex.compare_and_swap(true, false, SeqCst) {
-            self.data.root.reindex();
-        }
-    }
 }
 
 #[derive(Default, Clone, Debug)]
 struct WorldData {
     file_resolver: FileResolverImp,
     crate_graph: CrateGraph,
-    root: WritableSourceRoot,
+    root: Arc<WritableSourceRoot>,
     libs: Vec<Arc<ReadonlySourceRoot>>,
 }
 
diff --git a/crates/libanalysis/src/lib.rs b/crates/libanalysis/src/lib.rs
index ea3a287022..b4b7a6a304 100644
--- a/crates/libanalysis/src/lib.rs
+++ b/crates/libanalysis/src/lib.rs
@@ -14,11 +14,11 @@ extern crate salsa;
 
 mod symbol_index;
 mod module_map;
-pub(crate) mod module_map_db;
 mod imp;
 mod job;
 mod roots;
 mod db;
+mod queries;
 mod descriptors;
 
 use std::{
@@ -166,8 +166,8 @@ impl Analysis {
     pub fn file_syntax(&self, file_id: FileId) -> File {
         self.imp.file_syntax(file_id).clone()
     }
-    pub fn file_line_index(&self, file_id: FileId) -> LineIndex {
-        self.imp.file_line_index(file_id).clone()
+    pub fn file_line_index(&self, file_id: FileId) -> Arc<LineIndex> {
+        self.imp.file_line_index(file_id)
     }
     pub fn extend_selection(&self, file: &File, range: TextRange) -> TextRange {
         libeditor::extend_selection(file, range).unwrap_or(range)
@@ -177,19 +177,19 @@ impl Analysis {
     }
     pub fn syntax_tree(&self, file_id: FileId) -> String {
         let file = self.imp.file_syntax(file_id);
-        libeditor::syntax_tree(file)
+        libeditor::syntax_tree(&file)
     }
     pub fn join_lines(&self, file_id: FileId, range: TextRange) -> SourceChange {
         let file = self.imp.file_syntax(file_id);
-        SourceChange::from_local_edit(file_id, "join lines", libeditor::join_lines(file, range))
+        SourceChange::from_local_edit(file_id, "join lines", libeditor::join_lines(&file, range))
     }
     pub fn on_eq_typed(&self, file_id: FileId, offset: TextUnit) -> Option<SourceChange> {
         let file = self.imp.file_syntax(file_id);
-        Some(SourceChange::from_local_edit(file_id, "add semicolon", libeditor::on_eq_typed(file, offset)?))
+        Some(SourceChange::from_local_edit(file_id, "add semicolon", libeditor::on_eq_typed(&file, offset)?))
     }
     pub fn file_structure(&self, file_id: FileId) -> Vec<StructureNode> {
         let file = self.imp.file_syntax(file_id);
-        libeditor::file_structure(file)
+        libeditor::file_structure(&file)
     }
     pub fn symbol_search(&self, query: Query, token: &JobToken) -> Vec<(FileId, FileSymbol)> {
         self.imp.world_symbols(query, token)
@@ -208,15 +208,15 @@ impl Analysis {
     }
     pub fn runnables(&self, file_id: FileId) -> Vec<Runnable> {
         let file = self.imp.file_syntax(file_id);
-        libeditor::runnables(file)
+        libeditor::runnables(&file)
     }
     pub fn highlight(&self, file_id: FileId) -> Vec<HighlightedRange> {
         let file = self.imp.file_syntax(file_id);
-        libeditor::highlight(file)
+        libeditor::highlight(&file)
     }
     pub fn completions(&self, file_id: FileId, offset: TextUnit) -> Option<Vec<CompletionItem>> {
         let file = self.imp.file_syntax(file_id);
-        libeditor::scope_completion(file, offset)
+        libeditor::scope_completion(&file, offset)
     }
     pub fn assists(&self, file_id: FileId, range: TextRange) -> Vec<SourceChange> {
         self.imp.assists(file_id, range)
diff --git a/crates/libanalysis/src/module_map.rs b/crates/libanalysis/src/module_map.rs
index 79b88cac2f..a21f55fff1 100644
--- a/crates/libanalysis/src/module_map.rs
+++ b/crates/libanalysis/src/module_map.rs
@@ -1,281 +1,157 @@
-use relative_path::RelativePathBuf;
-use parking_lot::{RwLock, RwLockReadGuard, RwLockWriteGuard};
-use libsyntax2::{
-    File,
-    ast::{self, AstNode, NameOwner},
-    SyntaxNode, SmolStr,
-};
-use {FileId, imp::FileResolverImp};
-
-type SyntaxProvider<'a> = dyn Fn(FileId) -> &'a File + 'a;
-
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
-pub struct ModuleId(FileId);
-
-#[derive(Debug, Default)]
-pub struct ModuleMap {
-    state: RwLock<State>,
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum ChangeKind {
-    Delete, Insert, Update
-}
-
-impl Clone for ModuleMap {
-    fn clone(&self) -> ModuleMap {
-        let state = self.state.read().clone();
-        ModuleMap { state: RwLock::new(state) }
-    }
-}
-
-#[derive(Clone, Debug, Default)]
-struct State {
-    file_resolver: FileResolverImp,
-    changes: Vec<(FileId, ChangeKind)>,
-    links: Vec<Link>,
-}
-
-#[derive(Clone, Debug)]
-struct Link {
-    owner: ModuleId,
-    syntax: SyntaxNode,
-    points_to: Vec<ModuleId>,
-    problem: Option<Problem>,
-}
-
-#[derive(Clone, Debug)]
-pub enum Problem {
-    UnresolvedModule {
-        candidate: RelativePathBuf,
+use std::sync::Arc;
+use {
+    FileId,
+    db::{
+        Query, QueryRegistry, QueryCtx,
+        file_set
     },
-    NotDirOwner {
-        move_to: RelativePathBuf,
-        candidate: RelativePathBuf,
-    }
+    queries::file_syntax,
+    descriptors::{ModuleDescriptor, ModuleTreeDescriptor},
+};
+
+pub(crate) fn register_queries(reg: &mut QueryRegistry) {
+    reg.add(MODULE_DESCR, "MODULE_DESCR");
+    reg.add(MODULE_TREE, "MODULE_TREE");
 }
 
-impl ModuleMap {
-    pub fn new() -> ModuleMap {
-        Default::default()
+pub(crate) fn module_tree(ctx: QueryCtx) -> Arc<ModuleTreeDescriptor> {
+    ctx.get(MODULE_TREE, ())
+}
+
+const MODULE_DESCR: Query<FileId, ModuleDescriptor> = Query(30, |ctx, &file_id| {
+    let file = file_syntax(ctx, file_id);
+    ModuleDescriptor::new(file.ast())
+});
+
+const MODULE_TREE: Query<(), ModuleTreeDescriptor> = Query(31, |ctx, _| {
+    let file_set = file_set(ctx);
+    let mut files = Vec::new();
+    for &file_id in file_set.0.iter() {
+        let module_descr = ctx.get(MODULE_DESCR, file_id);
+        files.push((file_id, module_descr));
     }
-    pub fn update_file(&mut self, file_id: FileId, change_kind: ChangeKind) {
-        self.state.get_mut().changes.push((file_id, change_kind));
-    }
-    pub(crate) fn set_file_resolver(&mut self, file_resolver: FileResolverImp) {
-        self.state.get_mut().file_resolver = file_resolver;
-    }
-    pub fn module2file(&self, m: ModuleId) -> FileId {
-        m.0
-    }
-    pub fn file2module(&self, file_id: FileId) -> ModuleId {
-        ModuleId(file_id)
-    }
-    pub fn child_module_by_name<'a>(
-        &self,
-        parent_mod: ModuleId,
-        child_mod: &str,
-        syntax_provider: &SyntaxProvider,
-    ) -> Vec<ModuleId> {
-        self.links(syntax_provider)
-            .links
-            .iter()
-            .filter(|link| link.owner == parent_mod)
-            .filter(|link| link.name() == child_mod)
-            .filter_map(|it| it.points_to.first())
-            .map(|&it| it)
-            .collect()
+    ModuleTreeDescriptor::new(files.iter().map(|(file_id, descr)| (*file_id, &**descr)), &file_set.1)
+});
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+    use im;
+    use relative_path::{RelativePath, RelativePathBuf};
+    use {
+        db::{Db},
+        imp::FileResolverImp,
+        FileId, FileResolver,
+    };
+    use super::*;
+
+    #[derive(Debug)]
+    struct FileMap(im::HashMap<FileId, RelativePathBuf>);
+
+    impl FileResolver for FileMap {
+        fn file_stem(&self, file_id: FileId) -> String {
+            self.0[&file_id].file_stem().unwrap().to_string()
+        }
+        fn resolve(&self, file_id: FileId, rel: &RelativePath) -> Option<FileId> {
+            let path = self.0[&file_id].join(rel).normalize();
+            self.0.iter()
+                .filter_map(|&(id, ref p)| Some(id).filter(|_| p == &path))
+                .next()
+        }
     }
 
-    pub fn parent_modules(
-        &self,
-        m: ModuleId,
-        syntax_provider: &SyntaxProvider,
-    ) -> Vec<(ModuleId, SmolStr, SyntaxNode)> {
-        let mut res = Vec::new();
-        self.for_each_parent_link(m, syntax_provider, |link| {
-            res.push(
-                (link.owner, link.name().clone(), link.syntax.clone())
-            )
-        });
-        res
+    struct Fixture {
+        next_file_id: u32,
+        fm: im::HashMap<FileId, RelativePathBuf>,
+        db: Db,
     }
 
-    pub fn parent_module_ids(
-        &self,
-        m: ModuleId,
-        syntax_provider: &SyntaxProvider,
-    ) -> Vec<ModuleId> {
-        let mut res = Vec::new();
-        self.for_each_parent_link(m, syntax_provider, |link| res.push(link.owner));
-        res
-    }
-
-    fn for_each_parent_link(
-        &self,
-        m: ModuleId,
-        syntax_provider: &SyntaxProvider,
-        f: impl FnMut(&Link)
-    ) {
-        self.links(syntax_provider)
-            .links
-            .iter()
-            .filter(move |link| link.points_to.iter().any(|&it| it == m))
-            .for_each(f)
-    }
-
-    pub fn problems(
-        &self,
-        file: FileId,
-        syntax_provider: &SyntaxProvider,
-        mut cb: impl FnMut(ast::Name, &Problem),
-    ) {
-        let module = self.file2module(file);
-        let links = self.links(syntax_provider);
-        links
-            .links
-            .iter()
-            .filter(|link| link.owner == module)
-            .filter_map(|link| {
-                let problem = link.problem.as_ref()?;
-                Some((link, problem))
-            })
-            .for_each(|(link, problem)| cb(link.name_node(), problem))
-    }
-
-    fn links(
-        &self,
-        syntax_provider: &SyntaxProvider,
-    ) -> RwLockReadGuard<State> {
-        {
-            let guard = self.state.read();
-            if guard.changes.is_empty() {
-                return guard;
+    impl Fixture {
+        fn new() -> Fixture {
+            Fixture {
+                next_file_id: 1,
+                fm: im::HashMap::new(),
+                db: Db::new(),
             }
         }
-        let mut guard = self.state.write();
-        if !guard.changes.is_empty() {
-            guard.apply_changes(syntax_provider);
+        fn add_file(&mut self, path: &str, text: &str) -> FileId {
+            assert!(path.starts_with("/"));
+            let file_id = FileId(self.next_file_id);
+            self.next_file_id += 1;
+            self.fm.insert(file_id, RelativePathBuf::from(&path[1..]));
+            let mut new_state = self.db.state().clone();
+            new_state.file_map.insert(file_id, Arc::new(text.to_string()));
+            new_state.file_resolver = FileResolverImp::new(
+                Arc::new(FileMap(self.fm.clone()))
+            );
+            self.db = self.db.with_changes(new_state, &[file_id], true);
+            file_id
         }
-        assert!(guard.changes.is_empty());
-        RwLockWriteGuard::downgrade(guard)
-    }
-}
-
-impl State {
-    pub fn apply_changes(
-        &mut self,
-        syntax_provider: &SyntaxProvider,
-    ) {
-        let mut reresolve = false;
-        for (file_id, kind) in self.changes.drain(..) {
-            let mod_id = ModuleId(file_id);
-            self.links.retain(|link| link.owner != mod_id);
-            match kind {
-                ChangeKind::Delete => {
-                    for link in self.links.iter_mut() {
-                        link.points_to.retain(|&x| x != mod_id);
-                    }
-                }
-                ChangeKind::Insert => {
-                    let file = syntax_provider(file_id);
-                    self.links.extend(
-                        file
-                            .ast()
-                            .modules()
-                            .filter_map(|it| Link::new(mod_id, it))
-                    );
-                    reresolve = true;
-                }
-                ChangeKind::Update => {
-                    let file = syntax_provider(file_id);
-                    let resolver = &self.file_resolver;
-                    self.links.extend(
-                        file
-                            .ast()
-                            .modules()
-                            .filter_map(|it| Link::new(mod_id, it))
-                            .map(|mut link| {
-                                link.resolve(resolver);
-                                link
-                            })
-                    );
-                }
-            }
-        }
-        if reresolve {
-            for link in self.links.iter_mut() {
-                link.resolve(&self.file_resolver)
+        fn remove_file(&mut self, file_id: FileId) {
+            self.fm.remove(&file_id);
+            let mut new_state = self.db.state().clone();
+            new_state.file_map.remove(&file_id);
+            new_state.file_resolver = FileResolverImp::new(
+                Arc::new(FileMap(self.fm.clone()))
+            );
+            self.db = self.db.with_changes(new_state, &[file_id], true);
+        }
+        fn change_file(&mut self, file_id: FileId, new_text: &str) {
+            let mut new_state = self.db.state().clone();
+            new_state.file_map.insert(file_id, Arc::new(new_text.to_string()));
+            self.db = self.db.with_changes(new_state, &[file_id], false);
+        }
+        fn check_parent_modules(
+            &self,
+            file_id: FileId,
+            expected: &[FileId],
+            queries: &[(&'static str, u64)]
+        ) {
+            let (tree, events) = self.db.trace_query(|ctx| module_tree(ctx));
+            let actual = tree.parent_modules(file_id)
+                .into_iter()
+                .map(|link| link.owner(&tree))
+                .collect::<Vec<_>>();
+            assert_eq!(actual.as_slice(), expected);
+            let mut counts = HashMap::new();
+            events.into_iter()
+               .for_each(|event| *counts.entry(event).or_insert(0) += 1);
+            for &(query_id, expected_count) in queries.iter() {
+                let actual_count = *counts.get(&query_id).unwrap_or(&0);
+                assert_eq!(
+                    actual_count,
+                    expected_count,
+                    "counts for {} differ",
+                    query_id,
+                )
             }
+
         }
     }
+
+    #[test]
+    fn test_parent_module() {
+        let mut f = Fixture::new();
+        let foo = f.add_file("/foo.rs", "");
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
+
+        let lib = f.add_file("/lib.rs", "mod foo;");
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 0)]);
+
+        f.change_file(lib, "");
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
+
+        f.change_file(lib, "mod foo;");
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
+
+        f.change_file(lib, "mod bar;");
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
+
+        f.change_file(lib, "mod foo;");
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
+
+        f.remove_file(lib);
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 0)]);
+    }
 }
-
-impl Link {
-    fn new(owner: ModuleId, module: ast::Module) -> Option<Link> {
-        if module.name().is_none() {
-            return None;
-        }
-        let link = Link {
-            owner,
-            syntax: module.syntax().owned(),
-            points_to: Vec::new(),
-            problem: None,
-        };
-        Some(link)
-    }
-
-    fn name(&self) -> SmolStr {
-        self.name_node().text()
-    }
-
-    fn name_node(&self) -> ast::Name {
-        self.ast().name().unwrap()
-    }
-
-    fn ast(&self) -> ast::Module {
-        ast::Module::cast(self.syntax.borrowed())
-            .unwrap()
-    }
-
-    fn resolve(&mut self, file_resolver: &FileResolverImp) {
-        if !self.ast().has_semi() {
-            self.problem = None;
-            self.points_to = Vec::new();
-            return;
-        }
-        let (points_to, problem) = resolve_submodule(self.owner.0, &self.name(), file_resolver);
-        self.problem = problem;
-        self.points_to = points_to.into_iter().map(ModuleId).collect();
-    }
-}
-
-pub(crate) fn resolve_submodule(file_id: FileId, name: &SmolStr, file_resolver: &FileResolverImp) -> (Vec<FileId>, Option<Problem>) {
-    let mod_name = file_resolver.file_stem(file_id);
-    let is_dir_owner =
-        mod_name == "mod" || mod_name == "lib" || mod_name == "main";
-
-    let file_mod = RelativePathBuf::from(format!("../{}.rs", name));
-    let dir_mod = RelativePathBuf::from(format!("../{}/mod.rs", name));
-    let points_to: Vec<FileId>;
-    let problem: Option<Problem>;
-    if is_dir_owner {
-        points_to = [&file_mod, &dir_mod].iter()
-            .filter_map(|path| file_resolver.resolve(file_id, path))
-            .collect();
-        problem = if points_to.is_empty() {
-            Some(Problem::UnresolvedModule {
-                candidate: file_mod,
-            })
-        } else {
-            None
-        }
-    } else {
-        points_to = Vec::new();
-        problem = Some(Problem::NotDirOwner {
-            move_to: RelativePathBuf::from(format!("../{}/mod.rs", mod_name)),
-            candidate: file_mod,
-        });
-    }
-    (points_to, problem)
-}
diff --git a/crates/libanalysis/src/module_map_db/mod.rs b/crates/libanalysis/src/module_map_db/mod.rs
deleted file mode 100644
index adad943da5..0000000000
--- a/crates/libanalysis/src/module_map_db/mod.rs
+++ /dev/null
@@ -1,159 +0,0 @@
-use std::sync::Arc;
-use {
-    FileId,
-    db::{
-        Query, QueryRegistry, QueryCtx,
-        file_syntax, file_set
-    },
-    descriptors::{ModuleDescriptor, ModuleTreeDescriptor}
-};
-
-pub(crate) fn register_queries(reg: &mut QueryRegistry) {
-    reg.add(MODULE_DESCR, "MODULE_DESCR");
-}
-
-pub(crate) fn module_tree(ctx: QueryCtx) -> Arc<ModuleTreeDescriptor> {
-    ctx.get(MODULE_TREE, ())
-}
-
-impl<'a> QueryCtx<'a> {
-    fn module_descr(&self, file_id: FileId) -> Arc<ModuleDescriptor> {
-        self.get(MODULE_DESCR, file_id)
-    }
-}
-
-const MODULE_DESCR: Query<FileId, ModuleDescriptor> = Query(30, |ctx, &file_id| {
-    let file = file_syntax(ctx, file_id);
-    ModuleDescriptor::new(file.ast())
-});
-
-const MODULE_TREE: Query<(), ModuleTreeDescriptor> = Query(31, |ctx, _| {
-    let file_set = file_set(ctx);
-    let mut files = Vec::new();
-    for &file_id in file_set.0.iter() {
-        let module_descr = ctx.get(MODULE_DESCR, file_id);
-        files.push((file_id, module_descr));
-    }
-    ModuleTreeDescriptor::new(files.iter().map(|(file_id, descr)| (*file_id, &**descr)), &file_set.1)
-});
-
-#[cfg(test)]
-mod tests {
-    use std::collections::HashMap;
-    use im;
-    use relative_path::{RelativePath, RelativePathBuf};
-    use {
-        db::{Query, Db, State},
-        imp::FileResolverImp,
-        FileId, FileResolver,
-    };
-    use super::*;
-
-    #[derive(Debug)]
-    struct FileMap(im::HashMap<FileId, RelativePathBuf>);
-
-    impl FileResolver for FileMap {
-        fn file_stem(&self, file_id: FileId) -> String {
-            self.0[&file_id].file_stem().unwrap().to_string()
-        }
-        fn resolve(&self, file_id: FileId, rel: &RelativePath) -> Option<FileId> {
-            let path = self.0[&file_id].join(rel).normalize();
-            self.0.iter()
-                .filter_map(|&(id, ref p)| Some(id).filter(|_| p == &path))
-                .next()
-        }
-    }
-
-    struct Fixture {
-        next_file_id: u32,
-        fm: im::HashMap<FileId, RelativePathBuf>,
-        db: Db,
-    }
-
-    impl Fixture {
-        fn new() -> Fixture {
-            Fixture {
-                next_file_id: 1,
-                fm: im::HashMap::new(),
-                db: Db::new(),
-            }
-        }
-        fn add_file(&mut self, path: &str, text: &str) -> FileId {
-            assert!(path.starts_with("/"));
-            let file_id = FileId(self.next_file_id);
-            self.next_file_id += 1;
-            self.fm.insert(file_id, RelativePathBuf::from(&path[1..]));
-            let mut new_state = self.db.state().clone();
-            new_state.file_map.insert(file_id, Arc::new(text.to_string()));
-            new_state.file_resolver = FileResolverImp::new(
-                Arc::new(FileMap(self.fm.clone()))
-            );
-            self.db = self.db.with_changes(new_state, &[file_id], true);
-            file_id
-        }
-        fn remove_file(&mut self, file_id: FileId) {
-            self.fm.remove(&file_id);
-            let mut new_state = self.db.state().clone();
-            new_state.file_map.remove(&file_id);
-            new_state.file_resolver = FileResolverImp::new(
-                Arc::new(FileMap(self.fm.clone()))
-            );
-            self.db = self.db.with_changes(new_state, &[file_id], true);
-        }
-        fn change_file(&mut self, file_id: FileId, new_text: &str) {
-            let mut new_state = self.db.state().clone();
-            new_state.file_map.insert(file_id, Arc::new(new_text.to_string()));
-            self.db = self.db.with_changes(new_state, &[file_id], false);
-        }
-        fn check_parent_modules(
-            &self,
-            file_id: FileId,
-            expected: &[FileId],
-            queries: &[(&'static str, u64)]
-        ) {
-            let (actual, events) = self.db.trace_query(|ctx| {
-                ctx.get(PARENT_MODULE, file_id)
-            });
-            assert_eq!(actual.as_slice(), expected);
-            let mut counts = HashMap::new();
-            events.into_iter()
-               .for_each(|event| *counts.entry(event).or_insert(0) += 1);
-            for &(query_id, expected_count) in queries.iter() {
-                let actual_count = *counts.get(&query_id).unwrap_or(&0);
-                assert_eq!(
-                    actual_count,
-                    expected_count,
-                    "counts for {} differ",
-                    query_id,
-                )
-            }
-
-        }
-    }
-
-    #[test]
-    fn test_parent_module() {
-        let mut f = Fixture::new();
-        let foo = f.add_file("/foo.rs", "");
-        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
-
-        let lib = f.add_file("/lib.rs", "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
-        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 0)]);
-
-        f.change_file(lib, "");
-        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
-
-        f.change_file(lib, "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
-
-        f.change_file(lib, "mod bar;");
-        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
-
-        f.change_file(lib, "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
-
-        f.remove_file(lib);
-        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 0)]);
-    }
-}
diff --git a/crates/libanalysis/src/queries.rs b/crates/libanalysis/src/queries.rs
new file mode 100644
index 0000000000..9d6754fd47
--- /dev/null
+++ b/crates/libanalysis/src/queries.rs
@@ -0,0 +1,28 @@
+use std::sync::Arc;
+use libsyntax2::File;
+use libeditor::LineIndex;
+use {
+    FileId,
+    db::{Query, QueryCtx, QueryRegistry, file_text},
+};
+
+pub(crate) fn register_queries(reg: &mut QueryRegistry) {
+    reg.add(FILE_SYNTAX, "FILE_SYNTAX");
+    reg.add(FILE_LINES, "FILE_LINES");
+}
+
+pub(crate) fn file_syntax(ctx: QueryCtx, file_id: FileId) -> File {
+    (&*ctx.get(FILE_SYNTAX, file_id)).clone()
+}
+pub(crate) fn file_lines(ctx: QueryCtx, file_id: FileId) -> Arc<LineIndex> {
+    ctx.get(FILE_LINES, file_id)
+}
+
+const FILE_SYNTAX: Query<FileId, File> = Query(16, |ctx, file_id: &FileId| {
+    let text = file_text(ctx, *file_id);
+    File::parse(&*text)
+});
+const FILE_LINES: Query<FileId, LineIndex> = Query(17, |ctx, file_id: &FileId| {
+    let text = file_text(ctx, *file_id);
+    LineIndex::new(&*text)
+});
diff --git a/crates/libanalysis/src/roots.rs b/crates/libanalysis/src/roots.rs
index e9527eeff4..0e7253ba2f 100644
--- a/crates/libanalysis/src/roots.rs
+++ b/crates/libanalysis/src/roots.rs
@@ -1,6 +1,5 @@
 use std::{
     collections::HashMap,
-    time::Instant,
     sync::Arc,
     panic,
 };
@@ -13,83 +12,74 @@ use libsyntax2::File;
 use {
     FileId,
     imp::FileResolverImp,
-    module_map::{ModuleMap, ChangeKind},
     symbol_index::SymbolIndex,
     descriptors::{ModuleDescriptor, ModuleTreeDescriptor},
+    db::Db,
 };
 
 pub(crate) trait SourceRoot {
     fn contains(&self, file_id: FileId) -> bool;
-    fn module_tree(&self) -> Arc<ModuleTreeDescriptor> {
-        unimplemented!()
-    }
-    // fn module_map(&self) -> &ModuleMap;
-    fn lines(&self, file_id: FileId) -> &LineIndex;
-    fn syntax(&self, file_id: FileId) -> &File;
+    fn module_tree(&self) -> Arc<ModuleTreeDescriptor>;
+    fn lines(&self, file_id: FileId) -> Arc<LineIndex>;
+    fn syntax(&self, file_id: FileId) -> File;
     fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>);
 }
 
-#[derive(Clone, Default, Debug)]
+#[derive(Default, Debug)]
 pub(crate) struct WritableSourceRoot {
-    file_map: HashMap<FileId, Arc<(FileData, OnceCell<SymbolIndex>)>>,
-    module_map: ModuleMap,
+    db: Db,
 }
 
 impl WritableSourceRoot {
-    pub fn update(&mut self, file_id: FileId, text: Option<String>) {
-        let change_kind = if self.file_map.remove(&file_id).is_some() {
-            if text.is_some() {
-                ChangeKind::Update
-            } else {
-                ChangeKind::Delete
-            }
-        } else {
-            ChangeKind::Insert
-        };
-        self.module_map.update_file(file_id, change_kind);
-        self.file_map.remove(&file_id);
-        if let Some(text) = text {
-            let file_data = FileData::new(text);
-            self.file_map.insert(file_id, Arc::new((file_data, Default::default())));
-        }
-    }
-    pub fn set_file_resolver(&mut self, file_resolver: FileResolverImp) {
-        self.module_map.set_file_resolver(file_resolver)
-    }
-    pub fn reindex(&self) {
-        let now = Instant::now();
-        self.file_map
-            .par_iter()
-            .for_each(|(&file_id, data)| {
-                symbols(file_id, data);
-            });
-        info!("parallel indexing took {:?}", now.elapsed());
+    pub fn apply_changes(
+        &self,
+        changes: &mut dyn Iterator<Item=(FileId, Option<String>)>,
+        file_resolver: Option<FileResolverImp>,
+    ) -> WritableSourceRoot {
+        let resolver_changed = file_resolver.is_some();
+        let mut changed_files = Vec::new();
+        let mut new_state = self.db.state().clone();
 
-    }
-    fn data(&self, file_id: FileId) -> &FileData {
-        match self.file_map.get(&file_id) {
-            Some(data) => &data.0,
-            None => panic!("unknown file: {:?}", file_id),
+        for (file_id, text) in changes {
+            changed_files.push(file_id);
+            match text {
+                Some(text) => {
+                    new_state.file_map.insert(file_id, Arc::new(text));
+                },
+                None => {
+                    new_state.file_map.remove(&file_id);
+                }
+            }
+        }
+        if let Some(file_resolver) = file_resolver {
+            new_state.file_resolver = file_resolver
+        }
+        WritableSourceRoot {
+            db: self.db.with_changes(new_state, &changed_files, resolver_changed)
         }
     }
 }
 
 impl SourceRoot for WritableSourceRoot {
+    fn module_tree(&self) -> Arc<ModuleTreeDescriptor> {
+        self.db.make_query(::module_map::module_tree)
+    }
+
     fn contains(&self, file_id: FileId) -> bool {
-        self.file_map.contains_key(&file_id)
+        self.db.state().file_map.contains_key(&file_id)
     }
-    fn lines(&self, file_id: FileId) -> &LineIndex {
-        self.data(file_id).lines()
+    fn lines(&self, file_id: FileId) -> Arc<LineIndex> {
+        self.db.make_query(|ctx| ::queries::file_lines(ctx, file_id))
     }
-    fn syntax(&self, file_id: FileId) -> &File {
-        self.data(file_id).syntax()
+    fn syntax(&self, file_id: FileId) -> File {
+        self.db.make_query(|ctx| ::queries::file_syntax(ctx, file_id))
     }
     fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>) {
-        acc.extend(
-            self.file_map
-                .iter()
-                .map(|(&file_id, data)| symbols(file_id, data))
-        )
+        // acc.extend(
+        //     self.file_map
+        //         .iter()
+        //         .map(|(&file_id, data)| symbols(file_id, data))
+        // )
     }
 }
 
@@ -101,7 +91,7 @@ fn symbols(file_id: FileId, (data, symbols): &(FileData, OnceCell<SymbolIndex>))
 #[derive(Debug)]
 struct FileData {
     text: String,
-    lines: OnceCell<LineIndex>,
+    lines: OnceCell<Arc<LineIndex>>,
     syntax: OnceCell<File>,
 }
 
@@ -113,8 +103,8 @@ impl FileData {
             lines: OnceCell::new(),
         }
     }
-    fn lines(&self) -> &LineIndex {
-        self.lines.get_or_init(|| LineIndex::new(&self.text))
+    fn lines(&self) -> &Arc<LineIndex> {
+        self.lines.get_or_init(|| Arc::new(LineIndex::new(&self.text)))
     }
     fn syntax(&self) -> &File {
         let text = &self.text;
@@ -127,10 +117,6 @@ impl FileData {
             }
         }
     }
-    fn syntax_transient(&self) -> File {
-        self.syntax.get().map(|s| s.clone())
-            .unwrap_or_else(|| File::parse(&self.text))
-    }
 }
 
 #[derive(Debug)]
@@ -184,11 +170,11 @@ impl SourceRoot for ReadonlySourceRoot {
     fn contains(&self, file_id: FileId) -> bool {
         self.file_map.contains_key(&file_id)
     }
-    fn lines(&self, file_id: FileId) -> &LineIndex {
-        self.data(file_id).lines()
+    fn lines(&self, file_id: FileId) -> Arc<LineIndex> {
+        Arc::clone(self.data(file_id).lines())
     }
-    fn syntax(&self, file_id: FileId) -> &File {
-        self.data(file_id).syntax()
+    fn syntax(&self, file_id: FileId) -> File {
+        self.data(file_id).syntax().clone()
     }
     fn symbols<'a>(&'a self, acc: &mut Vec<&'a SymbolIndex>) {
         acc.push(&self.symbol_index)