The size, in bits, of the filter
The capacity, in entries, of the filter
The probability of a false positive that is tolerable
-The number of bits readily available to use for addresing filter bits
+The number of bits readily available to use for addressing filter bits
There is one major tunable that is not directly related to the above:
k: the number of bits set in the filter per entry
Based on these parameters, a combination of k=4 and k=5 provides the behavior
that bup needs. As such, I've implemented bloom addressing, adding and
checking functions in C for these two values. Because k=5 requires less space
-and gives better overall pfalse_positive perofrmance, it is preferred if a
+and gives better overall pfalse_positive performance, it is preferred if a
table with k=5 can represent the repository.
None of this tells us what max_pfalse_positive to choose.
Brandon Low <lostlogic@lostlogicx.com> 2011-02-04
"""
-import sys, os, math, mmap
+
+from __future__ import absolute_import
+import sys, os, math, mmap, struct
+
from bup import _helpers
-from bup.helpers import *
+from bup.helpers import (debug1, debug2, log, mmap_read, mmap_readwrite,
+ mmap_readwrite_private, unlink)
+
BLOOM_VERSION = 2
MAX_BITS_EACH = 32 # Kinda arbitrary, but 4 bytes per entry is pretty big
bloom_contains = _helpers.bloom_contains
bloom_add = _helpers.bloom_add
+# FIXME: check bloom create() and ShaBloom handling/ownership of "f".
+# The ownership semantics should be clarified since the caller needs
+# to know who is responsible for closing it.
class ShaBloom:
"""Wrapper which contains data from multiple index files. """
self.name = filename
self.rwfile = None
self.map = None
- assert(filename.endswith('.bloom'))
+ assert(filename.endswith(b'.bloom'))
if readwrite:
assert(expected > 0)
self.rwfile = f = f or open(filename, 'r+b')
# one bit flipped per memory page), let's use a "private" mmap,
# which defeats Linux's ability to flush it to disk. Then we'll
# flush it as one big lump during close().
- pages = os.fstat(f.fileno()).st_size / 4096 * 5 # assume k=5
+ pages = os.fstat(f.fileno()).st_size // 4096 * 5 # assume k=5
self.delaywrite = expected > pages
debug1('bloom: delaywrite=%r\n' % self.delaywrite)
if self.delaywrite:
self.rwfile = None
f = f or open(filename, 'rb')
self.map = mmap_read(f)
- got = str(self.map[0:4])
- if got != 'BLOM':
+ got = self.map[0:4]
+ if got != b'BLOM':
log('Warning: invalid BLOM header (%r) in %r\n' % (got, filename))
return self._init_failed()
ver = struct.unpack('!I', self.map[4:8])[0]
return self._init_failed()
self.bits, self.k, self.entries = struct.unpack('!HHI', self.map[8:16])
- idxnamestr = str(self.map[16 + 2**self.bits:])
+ idxnamestr = self.map[16 + 2**self.bits:]
if idxnamestr:
- self.idxnames = idxnamestr.split('\0')
+ self.idxnames = idxnamestr.split(b'\0')
else:
self.idxnames = []
self.map.flush()
self.rwfile.seek(16 + 2**self.bits)
if self.idxnames:
- self.rwfile.write('\0'.join(self.idxnames))
+ self.rwfile.write(b'\0'.join(self.idxnames))
self._init_failed()
def pfalse_positive(self, additional=0):
k = self.k
return 100*(1-math.exp(-k*float(n)/m))**k
- def add_idx(self, ix):
- """Add the object to the filter, return current pfalse_positive."""
+ def add(self, ids):
+ """Add the hashes in ids (packed binary 20-bytes) to the filter."""
if not self.map:
raise Exception("Cannot add to closed bloom")
- self.entries += bloom_add(self.map, ix.shatable, self.bits, self.k)
+ self.entries += bloom_add(self.map, ids, self.bits, self.k)
+
+ def add_idx(self, ix):
+ """Add the object to the filter."""
+ self.add(ix.shatable)
self.idxnames.append(os.path.basename(ix.name))
def exists(self, sha):
_total_searches += 1
if not self.map:
return None
- found, steps = bloom_contains(self.map, str(sha), self.bits, self.k)
+ found, steps = bloom_contains(self.map, sha, self.bits, self.k)
_total_steps += steps
return found
def create(name, expected, delaywrite=None, f=None, k=None):
"""Create and return a bloom filter for `expected` entries."""
- bits = int(math.floor(math.log(expected*MAX_BITS_EACH/8,2)))
+ bits = int(math.floor(math.log(expected * MAX_BITS_EACH // 8, 2)))
k = k or ((bits <= MAX_BLOOM_BITS[5]) and 5 or 4)
if bits > MAX_BLOOM_BITS[k]:
log('bloom: warning, max bits exceeded, non-optimal\n')
bits = MAX_BLOOM_BITS[k]
debug1('bloom: using 2^%d bytes and %d hash functions\n' % (bits, k))
f = f or open(name, 'w+b')
- f.write('BLOM')
+ f.write(b'BLOM')
f.write(struct.pack('!IHHI', BLOOM_VERSION, bits, k, 0))
assert(f.tell() == 16)
# NOTE: On some systems this will not extend+zerofill, but it does on
expected = 1
return ShaBloom(name, f=f, readwrite=True, expected=expected)
+
+def clear_bloom(dir):
+ unlink(os.path.join(dir, b'bup.bloom'))
projects / bup.git / blobdiff