switch rqlite to using cache=shared for in-memory databases

This is a little hairy. Looking at things like [1], it's evident that
golang's stdlib sql package doesn't work quite correctly with sqlite3's
in-memory databases. In particular, the connection pooling causes problems,
since there's no way to duplicate a connection to a particular in-memory
database.

So, we use cache=shared to force everything to point to the same in-memory
database. However, this causes some problems (mostly that untill the last
connection to this database is closed, the DB is not pruned). So we have to
do a little cleanup after ourselves in this case.

[1]: mattn/go-sqlite3#204

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>

db/db.go

@@ -81,7 +81,7 @@ func OpenWithDSN(dbPath, dsn string) (*DB, error) {
 
 // OpenInMemory opens an in-memory database.
 func OpenInMemory() (*DB, error) {
-	return OpenInMemoryWithDSN("")
+	return OpenInMemoryWithDSN("mode=memory&cache=shared")
 }
 
 // OpenInMemoryWithDSN opens an in-memory database with a specific DSN.

db/db_test.go

@@ -86,7 +86,7 @@ func Test_LoadInMemory(t *testing.T) {
 		t.Fatalf("unexpected results for query, expected %s, got %s", exp, got)
 	}
 
-	inmem, err := LoadInMemoryWithDSN(path, "")
+	inmem, err := LoadInMemoryWithDSN(path, "mode=memory&cache=shared")
 	if err != nil {
 		t.Fatalf("failed to create loaded in-memory database: %s", err.Error())
 	}

store/store_test.go

@@ -216,10 +216,8 @@ func Test_SingleNodeLoad(t *testing.T) {
 	s.WaitForLeader(10 * time.Second)
 
 	dump := `PRAGMA foreign_keys=OFF;
-BEGIN TRANSACTION;
 CREATE TABLE foo (id integer not null primary key, name text);
 INSERT INTO "foo" VALUES(1,'fiona');
-COMMIT;
 `
 	_, err := s.Execute([]string{dump}, false, false)
 	if err != nil {
@@ -250,7 +248,6 @@ func Test_SingleNodeSingleCommandTrigger(t *testing.T) {
 	s.WaitForLeader(10 * time.Second)
 
 	dump := `PRAGMA foreign_keys=OFF;
-BEGIN TRANSACTION;
 CREATE TABLE foo (id integer primary key asc, name text);
 INSERT INTO "foo" VALUES(1,'bob');
 INSERT INTO "foo" VALUES(2,'alice');
@@ -261,7 +258,6 @@ INSERT INTO "bar" VALUES(2,46);
 INSERT INTO "bar" VALUES(3,8);
 CREATE VIEW foobar as select name as Person, Age as age from foo inner join bar on foo.id == bar.nameid;
 CREATE TRIGGER new_foobar instead of insert on foobar begin insert into foo (name) values (new.Person); insert into bar (nameid, age) values ((select id from foo where name == new.Person), new.Age); end;
-COMMIT;
 `
 	_, err := s.Execute([]string{dump}, false, false)
 	if err != nil {
@@ -289,8 +285,6 @@ func Test_SingleNodeLoadNoStatements(t *testing.T) {
 	s.WaitForLeader(10 * time.Second)
 
 	dump := `PRAGMA foreign_keys=OFF;
-BEGIN TRANSACTION;
-COMMIT;
 `
 	_, err := s.Execute([]string{dump}, false, false)
 	if err != nil {
@@ -681,7 +675,12 @@ func mustNewStore(inmem bool) *Store {
 	path := mustTempDir()
 	defer os.RemoveAll(path)
 
-	cfg := NewDBConfig("", inmem)
+	dsn := ""
+	if inmem {
+		dsn = "mode=memory&cache=shared"
+	}
+
+	cfg := NewDBConfig(dsn, inmem)
 	s := New(&StoreConfig{
 		DBConf: cfg,
 		Dir:    path,