.

go/zodb/db.go

@@ -111,13 +111,6 @@ type DB struct {
 	// XXX δtail/δwait -> Storage. XXX or -> Cache? (so it is not duplicated many times for many DB case)
 }
 
-// δwaiter represents someone waiting for δtail.Head to become ≥ at.
-// XXX place
-type δwaiter struct {
-	at    Tid
-	ready chan struct{}
-}
-
 
 // NewDB creates new database handle.
 func NewDB(stor IStorage) *DB {
@@ -173,6 +166,12 @@ func (opt *ConnOptions) String() string {
 	return s
 }
 
+// δwaiter represents someone waiting for δtail.Head to become ≥ at.
+type δwaiter struct {
+	at    Tid
+	ready chan struct{}
+}
+
 // watcher receives events about new committed transactions and updates δtail.
 //
 // it also wakes up δtail waiters.
@@ -197,6 +196,12 @@ func (db *DB) watcher(watchq <-chan CommitEvent) { // XXX err ?
 				delete(db.δwait, w)
 			}
 		}
+
+		// forget older δtail entries
+		tcut := db.δtail.Head().Time().Add(-db.tδkeep)
+		δcut := TidFromTime(tcut)
+		db.δtail.ForgetBefore(δcut)
+
 		db.mu.Unlock()
 
 		// wakeup waiters outside of db.mu
@@ -261,7 +266,7 @@ func (db *DB) Open(ctx context.Context, opt *ConnOptions) (_ *Connection, err er
 	}
 
 	db.mu.Lock()
-	// unlock is either in db.open -> err, or in resyncAndDBUnlock
+	// unlock is either in resyncAndDBUnlock, or in db.openOrDBUnlock -> err
 
 	conn, err := db.openOrDBUnlock(ctx, at, opt.NoPool)
 	if err != nil {
@@ -274,7 +279,7 @@ func (db *DB) Open(ctx context.Context, opt *ConnOptions) (_ *Connection, err er
 // openOrDBUnlock is internal worker for Open.
 //
 // it returns either new connection, or connection from the pool.
-// returned connection does not neccessarily have .at=at, and have to go through .resync().
+// returned connection does not necessarily have .at=at, and have to go through .resync().
 //
 // must be called with db.mu locked.
 // db.mu is unlocked on error.
@@ -288,7 +293,7 @@ func (db *DB) openOrDBUnlock(ctx context.Context, at Tid, noPool bool) (*Connect
 
 retry:
 	for {
-		// check if we already have the exact match
+		// check if we already have an exact match
 		conn := db.get(at, at)
 		if conn != nil {
 			return conn, nil
@@ -450,16 +455,11 @@ func (conn *Connection) resyncAndDBUnlock(txn transaction.Transaction, at Tid) {
 	return
 }
 
-// get returns connection from db pool most close to at.
+// get returns connection from db pool most close to at with conn.at ∈ (atMin, at].
 //
-// it creates new one if there is no close-enough connection in the pool.	XXX -> no
-// XXX -> must be run with db.mu locked.
-func (db *DB) get(at Tid, FIXME ...Tid) *Connection {	// XXX FIXME added only to make it temp. compile
-	db.mu.Lock()
-	defer db.mu.Unlock()
-
-	// XXX at < δtail.Tail -> getHistoric; else -> here
-
+// if there is no such connection in the pool - nil is returned.
+// must be called with db.mu locked.
+func (db *DB) get(atMin, at Tid) *Connection {
 	l := len(db.pool)
 
 	// find pool index corresponding to at:
@@ -470,10 +470,11 @@ func (db *DB) get(at Tid, FIXME ...Tid) *Connection {	// XXX FIXME added only to
 
 	// search through window of X previous connections and find out the one
 	// with minimal distance to get to state @at. If all connections are too
-	// distant - create connection anew.
+	// distant - create connection anew.	// XXX no -> nil
 	//
 	// XXX search not only previous, but future too? (we can get back to
-	// past by invalidating what was later changed)
+	// past by invalidating what was later changed) (but likely it will
+	// hurt by destroying cache of more recent connection)
 	const X = 10 // XXX hardcoded
 	jδmin := -1
 	for j := i - X; j < i; j++ {
@@ -488,7 +489,7 @@ func (db *DB) get(at Tid, FIXME ...Tid) *Connection {	// XXX FIXME added only to
 	// nothing found or too distant
 	const Tnear = 10*time.Minute // XXX hardcoded
 	if jδmin < 0 || tabs(δtid(at, db.pool[jδmin].at)) > Tnear {
-		return newConnection(db, at)
+		return newConnection(db, at)	// XXX no -> nil
 	}
 
 	// reuse the connection
@@ -531,7 +532,7 @@ func (db *DB) put(conn *Connection) {
 	copy(db.pool[i+1:], db.pool[i:])
 	db.pool[i] = conn
 
-	// XXX GC too idle connections here?
+	// XXX GC too idle connections here? XXX
 }
 
 // ---- txn sync ----