def _read_page_data(self, page: int) -> bytes:
'''
read no.x page raw binary data from the db file
'''
page_start = page * self._tree_conf.page_size
data = util.read_from_file(self._fd, page_start,
page_start + self._tree_conf.page_size)
return data
def _load_page_gc(self):
'''
load all deprecated page used before into the memory
'''
for offset in range(1, self.last_page):
page_start = offset * self._tree_conf.page_size
page_type = util.read_from_file(self._fd, page_start,
constants.NODE_TYPE_LENGTH_LIMIT)
if page_type == 2: # _PageType.DEPRECATED_PAGE._value==2
yield offset
def get_page(self, page: int) -> bytes:
page_start = None
for store in (self._uncommited_pages, self._commited_pages):
page_start = store.get(page)
if page_start:
break
if not page_start:
return b''
return util.read_from_file(self._fd, page_start,
page_start + self._page_size)
def checkpoint(self):
'''
transfer the modified data back to the test_tree and close the WAL
'''
if self._uncommited_pages:
logger.warning('close WAL with uncommited data, discarding it')
util.file_flush_and_sync(self._fd)
for page, page_start in self._commited_pages.items():
page_data = util.read_from_file(self._fd, page_start,
page_start + self._page_size)
yield page, page_data
self._fd.close()
os.unlink(self._filename + '.xdb.wal')
def _load_next_frame(self):
start = self._fd.tell()
end = start + self.FRAME_HEADER_LENGTH
data = util.read_from_file(self._fd, start, end)
frame_type = int.from_bytes(data[0:constants.FRAME_TYPE_LENGTH_LIMIT],
constants.ENDIAN)
frame_type = FrameType(frame_type)
if frame_type is FrameType.PAGE:
self._fd.seek(end + self._page_size)
page = int.from_bytes(
data[constants.
FRAME_TYPE_LENGTH_LIMIT:constants.FRAME_TYPE_LENGTH_LIMIT +
constants.PAGE_ADDRESS_LIMIT])
self._index_frame(frame_type, page, end)
def _load_wal(self):
'''
load previous WAL generated when B Tree closed accidentally.
'''
self._fd.seek(0)
header_data = util.read_from_file(self, 0, constants.PAGE_LENGTH_LIMIT)
assert int.from_bytes(header_data, constants.ENDIAN) == self._page_size
while True:
try:
self._load_next_frame()
except util.EndOfFileError:
break
if self._uncommited_pages:
logger.warning('WAL has uncommited data, discarding it')
self._uncommited_pages = dict()