bup repositories are in Git format. This library allows us to
interact with the Git data structures.
"""
-import os, sys, zlib, time, subprocess, struct, stat, re, tempfile, math, glob
+import os, sys, zlib, time, subprocess, struct, stat, re, tempfile, glob
from bup.helpers import *
-from bup import _helpers, path
+from bup import _helpers, path, bloom
MIDX_VERSION = 4
SEEK_END=2 # os.SEEK_END is not defined in python 2.4
-"""Discussion of bloom constants for bup:
-
-There are four basic things to consider when building a bloom filter:
-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
-
-There is one major tunable that is not directly related to the above:
-k: the number of bits set in the filter per entry
-
-Here's a wall of numbers showing the relationship between k; the ratio between
-the filter size in bits and the entries in the filter; and pfalse_positive:
-
-mn|k=3 |k=4 |k=5 |k=6 |k=7 |k=8 |k=9 |k=10 |k=11
- 8|3.05794|2.39687|2.16792|2.15771|2.29297|2.54917|2.92244|3.41909|4.05091
- 9|2.27780|1.65770|1.40703|1.32721|1.34892|1.44631|1.61138|1.84491|2.15259
-10|1.74106|1.18133|0.94309|0.84362|0.81937|0.84555|0.91270|1.01859|1.16495
-11|1.36005|0.86373|0.65018|0.55222|0.51259|0.50864|0.53098|0.57616|0.64387
-12|1.08231|0.64568|0.45945|0.37108|0.32939|0.31424|0.31695|0.33387|0.36380
-13|0.87517|0.49210|0.33183|0.25527|0.21689|0.19897|0.19384|0.19804|0.21013
-14|0.71759|0.38147|0.24433|0.17934|0.14601|0.12887|0.12127|0.12012|0.12399
-15|0.59562|0.30019|0.18303|0.12840|0.10028|0.08523|0.07749|0.07440|0.07468
-16|0.49977|0.23941|0.13925|0.09351|0.07015|0.05745|0.05049|0.04700|0.04587
-17|0.42340|0.19323|0.10742|0.06916|0.04990|0.03941|0.03350|0.03024|0.02870
-18|0.36181|0.15765|0.08392|0.05188|0.03604|0.02748|0.02260|0.01980|0.01827
-19|0.31160|0.12989|0.06632|0.03942|0.02640|0.01945|0.01549|0.01317|0.01182
-20|0.27026|0.10797|0.05296|0.03031|0.01959|0.01396|0.01077|0.00889|0.00777
-21|0.23591|0.09048|0.04269|0.02356|0.01471|0.01014|0.00759|0.00609|0.00518
-22|0.20714|0.07639|0.03473|0.01850|0.01117|0.00746|0.00542|0.00423|0.00350
-23|0.18287|0.06493|0.02847|0.01466|0.00856|0.00555|0.00392|0.00297|0.00240
-24|0.16224|0.05554|0.02352|0.01171|0.00663|0.00417|0.00286|0.00211|0.00166
-25|0.14459|0.04779|0.01957|0.00944|0.00518|0.00316|0.00211|0.00152|0.00116
-26|0.12942|0.04135|0.01639|0.00766|0.00408|0.00242|0.00157|0.00110|0.00082
-27|0.11629|0.03595|0.01381|0.00626|0.00324|0.00187|0.00118|0.00081|0.00059
-28|0.10489|0.03141|0.01170|0.00515|0.00259|0.00146|0.00090|0.00060|0.00043
-29|0.09492|0.02756|0.00996|0.00426|0.00209|0.00114|0.00069|0.00045|0.00031
-30|0.08618|0.02428|0.00853|0.00355|0.00169|0.00090|0.00053|0.00034|0.00023
-31|0.07848|0.02147|0.00733|0.00297|0.00138|0.00072|0.00041|0.00025|0.00017
-32|0.07167|0.01906|0.00633|0.00250|0.00113|0.00057|0.00032|0.00019|0.00013
-
-Here's a table showing available repository size for a given pfalse_positive
-and three values of k (assuming we only use the 160 bit SHA1 for addressing the
-filter and 8192bytes per object):
-
-pfalse|obj k=4 |cap k=4 |obj k=5 |cap k=5 |obj k=6 |cap k=6
-2.500%|139333497228|1038.11 TiB|558711157|4262.63 GiB|13815755|105.41 GiB
-1.000%|104489450934| 778.50 TiB|436090254|3327.10 GiB|11077519| 84.51 GiB
-0.125%| 57254889824| 426.58 TiB|261732190|1996.86 GiB| 7063017| 55.89 GiB
-
-This eliminates pretty neatly any k>6 as long as we use the raw SHA for
-addressing.
-
-filter size scales linearly with repository size for a given k and pfalse.
-
-Here's a table of filter sizes for a 1 TiB repository:
-
-pfalse| k=3 | k=4 | k=5 | k=6
-2.500%| 138.78 MiB | 126.26 MiB | 123.00 MiB | 123.37 MiB
-1.000%| 197.83 MiB | 168.36 MiB | 157.58 MiB | 153.87 MiB
-0.125%| 421.14 MiB | 307.26 MiB | 262.56 MiB | 241.32 MiB
-
-For bup:
-* We want the bloom filter to fit in memory; if it doesn't, the k pagefaults
-per lookup will be worse than the two required for midx.
-* We want the pfalse_positive to be low enough that the cost of sometimes
-faulting on the midx doesn't overcome the benefit of the bloom filter.
-* We have readily available 160 bits for addressing the filter.
-* We want to be able to have a single bloom address entire repositories of
-reasonable size.
-
-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
-table with k=5 can represent the repository.
-
-None of this tells us what max_pfalse_positive to choose.
-
-Brandon Low <lostlogic@lostlogicx.com> 04-02-2011
-"""
-BLOOM_VERSION = 2
-MAX_BITS_EACH = 32 # Kinda arbitrary, but 4 bytes per entry is pretty big
-MAX_BLOOM_BITS = {4: 37, 5: 29} # 160/k-log2(8)
-MAX_PFALSE_POSITIVE = 1. # Totally arbitrary, needs benchmarking
-
verbose = 0
ignore_midx = 0
home_repodir = os.path.expanduser('~/.bup')
extract_bits = _helpers.extract_bits
-bloom_contains = _helpers.bloom_contains
-bloom_add = _helpers.bloom_add
-
-
-class ShaBloom:
- """Wrapper which contains data from multiple index files.
- """
- def __init__(self, filename, f=None, readwrite=False, expected=-1):
- self.name = filename
- self.rwfile = None
- self.map = None
- assert(filename.endswith('.bloom'))
- if readwrite:
- assert(expected > 0)
- self.rwfile = f = f or open(filename, 'r+b')
- f.seek(0)
-
- # Decide if we want to mmap() the pages as writable ('immediate'
- # write) or else map them privately for later writing back to
- # the file ('delayed' write). A bloom table's write access
- # pattern is such that we dirty almost all the pages after adding
- # very few entries. But the table is so big that dirtying
- # *all* the pages often exceeds Linux's default
- # /proc/sys/vm/dirty_ratio or /proc/sys/vm/dirty_background_ratio,
- # thus causing it to start flushing the table before we're
- # finished... even though there's more than enough space to
- # store the bloom table in RAM.
- #
- # To work around that behaviour, if we calculate that we'll
- # probably end up touching the whole table anyway (at least
- # 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
- self.delaywrite = expected > pages
- debug1('bloom: delaywrite=%r\n' % self.delaywrite)
- if self.delaywrite:
- self.map = mmap_readwrite_private(self.rwfile, close=False)
- else:
- self.map = mmap_readwrite(self.rwfile, close=False)
- else:
- self.rwfile = None
- f = f or open(filename, 'rb')
- self.map = mmap_read(f)
- got = str(self.map[0:4])
- if got != '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]
- if ver < BLOOM_VERSION:
- log('Warning: ignoring old-style (v%d) bloom %r\n'
- % (ver, filename))
- return self._init_failed()
- if ver > BLOOM_VERSION:
- log('Warning: ignoring too-new (v%d) bloom %r\n'
- % (ver, filename))
- 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:])
- if idxnamestr:
- self.idxnames = idxnamestr.split('\0')
- else:
- self.idxnames = []
-
- def _init_failed(self):
- if self.map:
- self.map = None
- if self.rwfile:
- self.rwfile.close()
- self.rwfile = None
- self.idxnames = []
- self.bits = self.entries = 0
-
- def valid(self):
- return self.map and self.bits
-
- def __del__(self):
- self.close()
-
- def close(self):
- if self.map and self.rwfile:
- debug2("bloom: closing with %d entries\n" % self.entries)
- self.map[12:16] = struct.pack('!I', self.entries)
- if self.delaywrite:
- self.rwfile.seek(0)
- self.rwfile.write(self.map)
- else:
- self.map.flush()
- self.rwfile.seek(16 + 2**self.bits)
- if self.idxnames:
- self.rwfile.write('\0'.join(self.idxnames))
- self._init_failed()
-
- def pfalse_positive(self, additional=0):
- n = self.entries + additional
- m = 8*2**self.bits
- 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."""
- if not self.map: raise Exception, "Cannot add to closed bloom"
- self.entries += bloom_add(self.map, ix.shatable, self.bits, self.k)
- self.idxnames.append(os.path.basename(ix.name))
-
- def exists(self, sha):
- """Return nonempty if the object probably exists in the bloom filter."""
- global _total_searches, _total_steps
- _total_searches += 1
- if not self.map: return None
- found, steps = bloom_contains(self.map, str(sha), self.bits, self.k)
- _total_steps += steps
- return found
-
- @classmethod
- def create(cls, 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)))
- 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(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
- # darwin, linux, bsd and solaris.
- f.truncate(16+2**bits)
- f.seek(0)
- if delaywrite != None and not delaywrite:
- # tell it to expect very few objects, forcing a direct mmap
- expected = 1
- return cls(name, f=f, readwrite=True, expected=expected)
-
- def __len__(self):
- return int(self.entries)
-
-
class PackMidx:
"""Wrapper which contains data from multiple index files.
Multiple index (.midx) files constitute a wrapper around index (.idx) files
d[full] = ix
bfull = os.path.join(self.dir, 'bup.bloom')
if self.bloom is None and os.path.exists(bfull):
- self.bloom = ShaBloom(bfull)
+ self.bloom = bloom.ShaBloom(bfull)
self.packs = list(set(d.values()))
self.packs.sort(lambda x,y: -cmp(len(x),len(y)))
if self.bloom and self.bloom.valid() and len(self.bloom) >= len(self):
projects / bup.git / blobdiff