def _step(self):
"""Progress one step through the batch, or fetch another physical
record if the batch is exhausted. Returns ``True`` so long as the
collection range has not been exceeded."""
# Previous record was non-batch, or previous batch exhausted. Need to
# fetch another record.
if not self._index:
# Have we visited maximum number of physical records? If so, stop
# iteration.
if not self._max_phys:
return False
self._max_phys -= 1
# Get the next record and decode its key. from_raw() returns None
# if the key's prefix doesn't match self.prefix, which indicates
# we've reached the end of the collection.
phys_key, self.raw = next(self.it, ('', ''))
self.keys = keylib.KeyList.from_raw(phys_key, self.prefix)
if not self.keys:
return False
self.phys_key = phys_key
lenk = len(self.keys)
# Single record.
if lenk == 1:
self.key = self.keys[0]
self.data = self.raw
self._index = 0
return True
# Decode the array of logical record offsets and save it, along
# with the decompressed concatenation of all records.
self._offsets, dstart = decode_offsets(self.raw)
self.concat = self.compressor.unpack(buffer(self.raw, dstart))
self._index = lenk
self._index -= 1
if self._reverse:
idx = self._index
else:
idx = (len(self.keys) - self._index) - 1
start = self._offsets[idx]
stop = self._offsets[idx + 1]
self.key = self.keys[-1 + -idx]
self.data = self.concat[start:stop]
return True
def _step(self):
"""Progress one step through the batch, or fetch another physical
record if the batch is exhausted. Returns ``True`` so long as the
collection range has not been exceeded."""
# Previous record was non-batch, or previous batch exhausted. Need to
# fetch another record.
if not self._index:
# Have we visited maximum number of physical records? If so, stop
# iteration.
if not self._max_phys:
return False
self._max_phys -= 1
# Get the next record and decode its key. from_raw() returns None
# if the key's prefix doesn't match self.prefix, which indicates
# we've reached the end of the collection.
phys_key, self.raw = next(self.it, ('', ''))
self.keys = keylib.KeyList.from_raw(phys_key, self.prefix)
if not self.keys:
return False
self.phys_key = phys_key
lenk = len(self.keys)
# Single record.
if lenk == 1:
self.key = self.keys[0]
self.data = self.raw
self._index = 0
return True
# Decode the array of logical record offsets and save it, along
# with the decompressed concatenation of all records.
self._offsets, dstart = decode_offsets(self.raw)
self.concat = self.compressor.unpack(buffer(self.raw, dstart))
self._index = lenk
self._index -= 1
if self._reverse:
idx = self._index
else:
idx = (len(self.keys) - self._index) - 1
start = self._offsets[idx]
stop = self._offsets[idx + 1]
self.key = self.keys[-1 + -idx]
self.data = self.concat[start:stop]
return True
def _logical_iter(self, it, reverse, prefix_s, prefix):
"""Generator that wraps a database engine iterator to yield logical
records. For compressed records, each physical record may contain
multiple physical records. This job's function is to make the
distinction invisible to reads."""
# * When iterating forward, if first yielded key lacks collection
# prefix, result of iteration is empty.
# * When iterating reverse, if first yielded key lacks collection
# prefix, discard, then behave as forward.
# * Records are discarded in the direction of iteration until
# startpred() or not self.prefix.
# * Records are yielded following startpred() until not endpred() or
# not self.prefix.
prefix = prefix or ()
tup = next(it, None)
if tup and tup[0][:len(prefix_s)] == prefix_s:
it = itertools.chain((tup,), it)
for key, value in it:
keys = keylib.unpacks(prefix_s, key)
if not keys:
return
lenk = len(keys)
if lenk == 1:
key = keylib.Key(*(prefix + keys[0]))
yield False, key, self._decompress(value)
else: # Batch record.
offsets, dstart = decode_offsets(value)
data = self._decompress(buffer(value, dstart))
if reverse:
stop = -1
step = -1
i = lenk
else:
stop = lenk
step = 1
i = 0
while i != stop:
key = keys[-1 - i]
offs = offsets[i]
size = offsets[i+1] - offs
key = keylib.Key(*(prefix + key))
yield True, key, buffer(data, offs, size)
i += step
