add PageSize to Option struct

Configure the db page size at runtime. Makes cross-arch debugging a bit easier.

db.go

@@ -200,6 +200,11 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 	// Default values for test hooks
 	db.ops.writeAt = db.file.WriteAt
 
+	if db.pageSize = options.PageSize; db.pageSize == 0 {
+		// Set the default page size to the OS page size.
+		db.pageSize = defaultPageSize
+	}
+
 	// Initialize the database if it doesn't exist.
 	if info, err := db.file.Stat(); err != nil {
 		return nil, err
@@ -211,20 +216,21 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 	} else {
 		// Read the first meta page to determine the page size.
 		var buf [0x1000]byte
-		if _, err := db.file.ReadAt(buf[:], 0); err == nil {
+		// If we can't read the page size, but can read a page, assume
-			m := db.pageInBuffer(buf[:], 0).meta()
+		// it's the same as the OS or one given -- since that's how the
-			if err := m.validate(); err != nil {
+		// page size was chosen in the first place.
-				// If we can't read the page size, we can assume it's the same
+		//
-				// as the OS -- since that's how the page size was chosen in the
+		// If the first page is invalid and this OS uses a different
-				// first place.
+		// page size than what the database was created with then we
-				//
+		// are out of luck and cannot access the database.
-				// If the first page is invalid and this OS uses a different
+		//
-				// page size than what the database was created with then we
+		// TODO: scan for next page
-				// are out of luck and cannot access the database.
+		if bw, err := db.file.ReadAt(buf[:], 0); err == nil && bw == len(buf) {
-				db.pageSize = defaultPageSize
+			if m := db.pageInBuffer(buf[:], 0).meta(); m.validate() == nil {
-			} else {
 				db.pageSize = int(m.pageSize)
 			}
+		} else {
+			return nil, ErrInvalid
 		}
 	}
 
@@ -370,9 +376,6 @@ func (db *DB) mmapSize(size int) (int, error) {
 
 // init creates a new database file and initializes its meta pages.
 func (db *DB) init() error {
-	// Set the page size to the OS page size.
-	db.pageSize = defaultPageSize
-
 	// Create two meta pages on a buffer.
 	buf := make([]byte, db.pageSize*4)
 	for i := 0; i < 2; i++ {
@@ -999,6 +1002,9 @@ type Options struct {
 	// If initialMmapSize is smaller than the previous database size,
 	// it takes no effect.
 	InitialMmapSize int
+
+	// PageSize overrides the default OS page size.
+	PageSize int
 }
 
 // DefaultOptions represent the options used if nil options are passed into Open().

db_test.go

@@ -423,6 +423,22 @@ func TestDB_Open_InitialMmapSize(t *testing.T) {
 	}
 }
 
+// TestOpen_BigPage checks the database uses bigger pages when
+// changing PageSize.
+func TestOpen_BigPage(t *testing.T) {
+	pageSize := os.Getpagesize()
+
+	db1 := MustOpenWithOption(&bolt.Options{PageSize: pageSize * 2})
+	defer db1.MustClose()
+
+	db2 := MustOpenWithOption(&bolt.Options{PageSize: pageSize * 4})
+	defer db2.MustClose()
+
+	if db1sz, db2sz := fileSize(db1.f), fileSize(db2.f); db1sz >= db2sz {
+		t.Errorf("expected %d < %d", db1sz, db2sz)
+	}
+}
+
 // TestOpen_RecoverFreeList tests opening the DB with free-list
 // write-out after no free list sync will recover the free list
 // and write it out.