borg/darc/store.py

from ConfigParser import RawConfigParser
import errno
import fcntl
import os
import shutil
import struct
import tempfile
import unittest
from zlib import crc32

from .hashindex import NSIndex, BandIndex
from .helpers import IntegrityError, read_set, write_set
from .lrucache import LRUCache


class Store(object):
    """Filesystem based transactional key value store

    On disk layout:
    dir/README
    dir/config
    dir/bands/<X / BANDS_PER_DIR>/<X>
    dir/indexes/<NS>
    """
    DEFAULT_MAX_BAND_SIZE = 5 * 1024 * 1024
    DEFAULT_BANDS_PER_DIR = 10000

    class DoesNotExist(KeyError):
        """Requested key does not exist"""


    def __init__(self, path, create=False):
        self.txn_active = False
        if create:
            self.create(path)
        self.open(path)

    def create(self, path):
        """Create a new empty store at `path`
        """
        if os.path.exists(path) and (not os.path.isdir(path) or os.listdir(path)):
            raise Exception('Path "%s" already exists' % path)
        if not os.path.exists(path):
            os.mkdir(path)
        with open(os.path.join(path, 'README'), 'wb') as fd:
            fd.write('This is a DARC store')
        os.mkdir(os.path.join(path, 'bands'))
        os.mkdir(os.path.join(path, 'indexes'))
        config = RawConfigParser()
        config.add_section('store')
        config.set('store', 'version', '1')
        config.set('store', 'id', os.urandom(32).encode('hex'))
        config.set('store', 'bands_per_dir', self.DEFAULT_BANDS_PER_DIR)
        config.set('store', 'max_band_size', self.DEFAULT_MAX_BAND_SIZE)
        config.add_section('state')
        config.set('state', 'next_band', '0')
        config.set('state', 'tid', '0')
        with open(os.path.join(path, 'config'), 'w') as fd:
            config.write(fd)

    def open(self, path):
        self.path = path
        if not os.path.isdir(path):
            raise Exception('%s Does not look like a darc store' % path)
        self.lock_fd = open(os.path.join(path, 'README'), 'r+')
        fcntl.flock(self.lock_fd, fcntl.LOCK_EX)
        self.rollback()
        self.config = RawConfigParser()
        self.config.read(os.path.join(path, 'config'))
        if self.config.getint('store', 'version') != 1:
            raise Exception('%s Does not look like a darc store')
        self.id = self.config.get('store', 'id').decode('hex')
        self.tid = self.config.getint('state', 'tid')
        next_band = self.config.getint('state', 'next_band')
        max_band_size = self.config.getint('store', 'max_band_size')
        bands_per_dir = self.config.getint('store', 'bands_per_dir')
        self.io = BandIO(self.path, next_band, max_band_size, bands_per_dir)
        self.io.cleanup()

    def delete_bands(self):
        delete_path = os.path.join(self.path, 'indexes', 'delete')
        if os.path.exists(delete_path):
            bands = self.get_index('bands')
            for band in read_set(delete_path):
                assert bands.pop(band, 0) == 0
                self.io.delete_band(band, missing_ok=True)
            os.unlink(delete_path)

    def begin_txn(self):
        txn_dir = os.path.join(self.path, 'txn.tmp')
        # Initialize transaction snapshot
        os.mkdir(txn_dir)
        shutil.copytree(os.path.join(self.path, 'indexes'),
                        os.path.join(txn_dir, 'indexes'))
        shutil.copy(os.path.join(self.path, 'config'), txn_dir)
        os.rename(os.path.join(self.path, 'txn.tmp'),
                  os.path.join(self.path, 'txn.active'))
        self.compact = set()
        self.txn_active = True

    def close(self):
        self.rollback()
        self.lock_fd.close()

    def commit(self):
        """Commit transaction, `tid` will be increased by 1
        """
        self.compact_bands()
        self.io.close()
        self.tid += 1
        self.config.set('state', 'tid', self.tid)
        self.config.set('state', 'next_band', self.io.band + 1)
        with open(os.path.join(self.path, 'config'), 'w') as fd:
            self.config.write(fd)
        for i in self.indexes.values():
            i.flush()
        # If we crash before this line, the transaction will be
        # rolled back by open()
        os.rename(os.path.join(self.path, 'txn.active'),
                  os.path.join(self.path, 'txn.commit'))
        self.rollback()

    def compact_bands(self):
        """Compact sparse bands by copying data into new bands
        """
        if not self.compact:
            return
        self.io.close_band()
        def lookup(ns, key):
            return key in self.get_index(ns)
        bands = self.get_index('bands')
        for band in self.compact:
            if bands[band] > 0:
                for ns, key, data in self.io.iter_objects(band, lookup):
                    new_band, offset = self.io.write(ns, key, data)
                    self.indexes[ns][key] = new_band, offset
                    bands[band] -= 1
                    bands.setdefault(new_band, 0)
                    bands[new_band] += 1
        write_set(self.compact, os.path.join(self.path, 'indexes', 'delete'))

    def rollback(self):
        """
        """
        # Commit any half committed transaction
        if os.path.exists(os.path.join(self.path, 'txn.commit')):
            self.delete_bands()
            os.rename(os.path.join(self.path, 'txn.commit'),
                      os.path.join(self.path, 'txn.tmp'))
        # Roll back active transaction
        txn_dir = os.path.join(self.path, 'txn.active')
        if os.path.exists(txn_dir):
            shutil.rmtree(os.path.join(self.path, 'indexes'))
            shutil.copytree(os.path.join(txn_dir, 'indexes'),
                            os.path.join(self.path, 'indexes'))
            shutil.copy(os.path.join(txn_dir, 'config'), self.path)
            os.rename(txn_dir, os.path.join(self.path, 'txn.tmp'))
        # Remove partially removed transaction
        if os.path.exists(os.path.join(self.path, 'txn.tmp')):
            shutil.rmtree(os.path.join(self.path, 'txn.tmp'))
        self.indexes = {}
        self.txn_active = False

    def get_index(self, ns):
        try:
            return self.indexes[ns]
        except KeyError:
            if ns == 'bands':
                filename = os.path.join(self.path, 'indexes', 'bands')
                cls = BandIndex
            else:
                filename = os.path.join(self.path, 'indexes', 'ns%d' % ns)
                cls = NSIndex
            if os.path.exists(filename):
                self.indexes[ns] = cls(filename)
            else:
                self.indexes[ns] = cls.create(filename)
            return self.indexes[ns]

    def get(self, ns, id):
        try:
            band, offset = self.get_index(ns)[id]
            return self.io.read(band, offset)
        except KeyError:
            raise self.DoesNotExist

    def put(self, ns, id, data):
        if not self.txn_active:
            self.begin_txn()
        band, offset = self.io.write(ns, id, data)
        bands = self.get_index('bands')
        bands.setdefault(band, 0)
        bands[band] += 1
        self.get_index(ns)[id] = band, offset

    def delete(self, ns, id):
        if not self.txn_active:
            self.begin_txn()
        try:
            band, offset = self.get_index(ns).pop(id)
            self.get_index('bands')[band] -= 1
            self.compact.add(band)
        except KeyError:
            raise self.DoesNotExist

    def list(self, ns, marker=None, limit=1000000):
        return [key for (key, value) in
                self.get_index(ns).iteritems(marker=marker, limit=limit)]


class BandIO(object):

    header_fmt = struct.Struct('<iBiB32s')
    assert header_fmt.size == 42

    def __init__(self, path, nextband, limit, bands_per_dir, capacity=100):
        self.path = path
        self.fds = LRUCache(capacity)
        self.band = nextband
        self.limit = limit
        self.bands_per_dir = bands_per_dir
        self.offset = 0

    def close(self):
        for band in self.fds.keys():
            self.fds.pop(band).close()

    def cleanup(self):
        """Delete band files left by aborted transactions
        """
        band = self.band
        while True:
            filename = self.band_filename(band)
            if not os.path.exists(filename):
                break
            os.unlink(filename)
            band += 1

    def band_filename(self, band):
        return os.path.join(self.path, 'bands', str(band / self.bands_per_dir), str(band))

    def get_fd(self, band, write=False):
        try:
            return self.fds[band]
        except KeyError:
            if write and band % 1000 == 0:
                dirname = os.path.join(self.path, 'bands', str(band / self.bands_per_dir))
                if not os.path.exists(dirname):
                    os.mkdir(dirname)
            fd = open(self.band_filename(band), write and 'w+' or 'rb')
            self.fds[band] = fd
            return fd

    def delete_band(self, band, missing_ok=False):
        try:
            os.unlink(self.band_filename(band))
        except OSError, e:
            if not missing_ok or e.errno != errno.ENOENT:
                raise

    def read(self, band, offset):
        fd = self.get_fd(band)
        fd.seek(offset)
        data = fd.read(self.header_fmt.size)
        size, magic, hash, ns, id = self.header_fmt.unpack(data)
        assert magic == 0
        data = fd.read(size - self.header_fmt.size)
        if crc32(data) != hash:
            raise IntegrityError('Band checksum mismatch')
        return data

    def iter_objects(self, band, lookup):
        fd = self.get_fd(band)
        fd.seek(0)
        assert fd.read(8) == 'DARCBAND'
        offset = 8
        data = fd.read(self.header_fmt.size)
        while data:
            size, magic, hash, ns, key = self.header_fmt.unpack(data)
            assert magic == 0
            offset += size
            if lookup(ns, key):
                data = fd.read(size - self.header_fmt.size)
                if crc32(data) != hash:
                    raise IntegrityError('Band checksum mismatch')
                yield ns, key, data
            else:
                fd.seek(offset)
            data = fd.read(self.header_fmt.size)

    def write(self, ns, id, data):
        size = len(data) + self.header_fmt.size
        if self.offset and self.offset + size > self.limit:
            self.close_band()
        fd = self.get_fd(self.band, write=True)
        fd.seek(self.offset)
        if self.offset == 0:
            fd.write('DARCBAND')
            self.offset = 8
        offset = self.offset
        hash = crc32(data)
        fd.write(self.header_fmt.pack(size, 0, hash, ns, id))
        fd.write(data)
        self.offset += size
        return self.band, offset

    def close_band(self):
        self.band += 1
        self.offset = 0


class StoreTestCase(unittest.TestCase):

    def setUp(self):
        self.tmppath = tempfile.mkdtemp()
        self.store = Store(os.path.join(self.tmppath, 'store'), create=True)

    def tearDown(self):
        shutil.rmtree(self.tmppath)

    def test1(self):
        self.assertEqual(self.store.tid, 0)
        for x in range(100):
            self.store.put(0, '%-32d' % x, 'SOMEDATA')
        key50 = '%-32d' % 50
        self.assertEqual(self.store.get(0, key50), 'SOMEDATA')
        self.store.delete(0, key50)
        self.assertRaises(self.store.DoesNotExist, lambda: self.store.get(0, key50))
        self.store.commit()
        self.assertEqual(self.store.tid, 1)
        self.store.close()
        store2 = Store(os.path.join(self.tmppath, 'store'))
        self.assertEqual(store2.tid, 1)
        keys = store2.list(0)
        for x in range(50):
            key = '%-32d' % x
            self.assertEqual(store2.get(0, key), 'SOMEDATA')
        self.assertRaises(store2.DoesNotExist, lambda: store2.get(0, key50))
        assert key50 not in keys
        for x in range(51, 100):
            key = '%-32d' % x
            assert key in keys
            self.assertEqual(store2.get(0, key), 'SOMEDATA')
        self.assertEqual(len(keys), 99)
        for x in range(50):
            key = '%-32d' % x
            store2.delete(0, key)
        self.assertEqual(len(store2.list(0)), 49)
        for x in range(51, 100):
            key = '%-32d' % x
            store2.delete(0, key)
        self.assertEqual(len(store2.list(0)), 0)


def suite():
    return unittest.TestLoader().loadTestsFromTestCase(StoreTestCase)

if __name__ == '__main__':
    unittest.main()