go: sqle: auto_gc: Responding to PR feedback. Comments and cleanup.

go/cmd/dolt/commands/engine/sqlengine.go

@@ -115,6 +115,13 @@ func NewSqlEngine(
 		return nil, err
 	}
 
+	// Make a copy of the databases. |all| is going to be provided
+	// as the set of all initial databases to dsqle
+	// DatabaseProvider. |dbs| is only the databases that came
+	// from MultiRepoEnv, and they are all real databases based on
+	// DoltDB instances. |all| is going to include some extension,
+	// informational databases like |dolt_cluster| sometimes,
+	// depending on config.
 	all := make([]dsess.SqlDatabase, len(dbs))
 	copy(all, dbs)
 

go/libraries/doltcore/doltdb/doltdb.go

@@ -1919,16 +1919,12 @@ func (ddb *DoltDB) IsTableFileStore() bool {
 func (ddb *DoltDB) ChunkJournal() *nbs.ChunkJournal {
 	cs := datas.ChunkStoreFromDatabase(ddb.db)
 
-	var store *nbs.NomsBlockStore
-	generationalNBS, ok := cs.(*nbs.GenerationalNBS)
-	if ok {
-		store = generationalNBS.NewGen().(*nbs.NomsBlockStore)
-	} else {
-		store = cs.(*nbs.NomsBlockStore)
+	if generationalNBS, ok := cs.(*nbs.GenerationalNBS); ok {
+		cs = generationalNBS.NewGen()
 	}
 
-	if store != nil {
-		return store.ChunkJournal()
+	if nbsStore, ok := cs.(*nbs.NomsBlockStore); ok {
+		return nbsStore.ChunkJournal()
 	} else {
 		return nil
 	}

go/libraries/doltcore/sqle/auto_gc.go

@@ -154,13 +154,17 @@ func (c *AutoGCController) newCommitHook(name string) doltdb.CommitHook {
 type autoGCCommitHook struct {
 	c    *AutoGCController
 	name string
-	// Always non-nil, if this channel delivers this channel
-	// delivers when no GC is currently running.
+	// When |done| is closed, there is no GC currently running or
+	// pending for this database. If it is open, then there is a
+	// pending request for GC or a GC is currently running. Once
+	// |done| is closed, we can check for auto GC conditions on
+	// the database to see if we should request a new GC.
 	done chan struct{}
 	// It simplifies the logic and efficiency of the
-	// implementation a bit to have a
-	// we can send. It becomes our new |done| channel on a
-	// successful send.
+	// implementation a bit to have an already allocated 	// in the commit hook.
+channel
+	// we can try to send, which will become our new |done|
+	// channel once we send it successfully.
 	next chan struct{}
 	// |done| and |next| are mutable and |Execute| can be called
 	// concurrently. We protect them with |mu|.