zodb: NewDB += option to set live cache control on created connections

WCFS needs this to run tests faster.

In general it is also a good idea to pass options to DB constructor, in
particular options that affect live cache size, or other properties, for
further created connections.

go/zodb/btree/btree_test.go

-// Copyright (C) 2018-2019  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -105,7 +105,7 @@ func TestBTree(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	db := zodb.NewDB(stor)
+	db := zodb.NewDB(stor, &zodb.DBOptions{})
 	defer func() {
 		err := db.Close(); X(err)
 	}()

go/zodb/connection.go

-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -180,7 +180,7 @@ const (
 
 // newConnection creates new Connection associated with db.
 func newConnection(db *DB, at Tid) *Connection {
-	return &Connection{
+	conn := &Connection{
 		db:    db,
 		at:    at,
 		cache: LiveCache{
@@ -188,6 +188,10 @@ func newConnection(db *DB, at Tid) *Connection {
 			objtab: make(map[Oid]*weak.Ref),
 		},
 	}
+	if cc := db.opt.CacheControl; cc != nil {
+		conn.cache.SetControl(cc)
+	}
+	return conn
 }
 
 // DB returns database handle under which the connection was opened.

go/zodb/db.go

-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -48,6 +48,8 @@ type DB struct {
 	stor   IStorage
 	watchq chan Event // we are watching .stor via here
 
+	opt *DBOptions
+
 	down     chan struct{} // ready when DB is no longer operational
 	downOnce sync.Once     // shutdown may be due to both Close and IO error in watcher
 	downErr  error         // reason for shutdown
@@ -121,15 +123,23 @@ type DB struct {
 	// (so it is not duplicated many times for many DB case)
 }
 
+// DBOptions describes options to NewDB.
+type DBOptions struct {
+	// CacheControl, if !nil, is set as default live cache control for
+	// newly created connections.
+	CacheControl LiveCacheControl
+}
 
 // NewDB creates new database handle.
 //
 // Created database handle must be closed when no longer needed.
-func NewDB(stor IStorage) *DB {
-	// XXX db options?
+func NewDB(stor IStorage, opt *DBOptions) *DB {
+	// copy opts in case caller will change them later
+	opt_ := *opt
 	db := &DB{
 		stor:   stor,
 		watchq: make(chan Event),
+		opt:    &opt_,
 		down:   make(chan struct{}),
 		hwait:  make(map[hwaiter]struct{}),
 

go/zodb/persistent_test.go

-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -276,7 +276,7 @@ func (t *tDB) Reopen() {
 		ReadOnly: true,
 		NoCache: !t.rawcache,
 	}); X(err)
-	db := NewDB(stor)
+	db := NewDB(stor, &DBOptions{})
 	t.stor = stor
 	t.db = db
 }