wip

tools/reflink

+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+from __future__ import print_function
+import argparse, logging, os, threading, sys
+from bisect import insort
+from collections import defaultdict
+from contextlib import contextmanager
+from datetime import timedelta
+from functools import partial
+from io import BytesIO
+from operator import attrgetter
+from select import select
+from time import gmtime, time
+from Queue import Empty, Queue
+
+from msgpack import dumps, loads
+from pkg_resources import iter_entry_points
+import ZODB
+from persistent.TimeStamp import TimeStamp
+from ZODB._compat import PersistentUnpickler
+from ZODB.broken import Broken
+from ZODB.POSException import ConflictError, POSKeyError
+from ZODB.serialize import referencesf
+from ZODB.utils import p64, u64, z64
+
+TXN_GC_DESC = 'neoppod.git/reflink/gc@%x'
+VERSION = 1
+
+logger = logging.getLogger('reflink')
+
+try:
+    from ZODB.Connection import TransactionMetaData
+except ImportError: # BBB: ZODB < 5
+    from ZODB.BaseStorage import TransactionRecord
+    TransactionMetaData = lambda user='', description='', extension=None: \
+        TransactionRecord(None, None, user, description, extension)
+
+def checkAPI(storage):
+    try:
+        storage.app.oids.__call__
+    except Exception:
+        raise NotImplementedError(
+            "Unable to iterate over all non-deleted OIDs of the"
+            " reflink ZODB, which is required for a full GC (or a dump)."
+            " Only NEO is known to have this non-standard API.")
+
+def openStorage(uri):
+    scheme = uri[:uri.find(':')]
+    for ep in iter_entry_points('zodburi.resolvers'):
+        if ep.name == scheme:
+            factory, dbkw = ep.load()(uri)
+            if dbkw:
+                raise ValueError("Unexpected database options: %r" % dbkw)
+            return factory()
+    raise KeyError('No resolver found for uri: %s' % uri)
+
+def inc64(tid):
+    return p64(u64(tid) + 1)
+
+def tidFromTime(t):
+    return TimeStamp(*gmtime(t)[:5]+(t%60,)).raw()
+
+
+class InvalidationListener(object):
+
+    def __init__(self, storage, tid):
+        self.last_gc = tid
+        self._lock = l = threading.Lock()
+        # Py3: use threading.Event (which has efficient timeout)
+        self._new_pipe = os.pipe()
+        self._new_flag = False
+        storage.registerDB(self)
+        self.invalidateCache = lambda: None
+        ltid = storage.lastTransaction()
+        del self.invalidateCache
+        with l:
+            if hasattr(self, 'last_tid'):
+                return
+            self.last_tid = ltid
+
+    def invalidateCache(self):
+        raise NotImplementedError
+
+    def invalidate(self, transaction_id, oids, version=''):
+        with self._lock:
+            self.last_tid = transaction_id
+            if not self._new_flag:
+                self._new_flag = True
+                os.write(self._new_pipe[1], '\0')
+
+    def tpc_finish(self, tid):
+        self.last_tid = self.last_gc = tid
+
+    def wait(self, tid, timeout):
+        with self._lock:
+            if tid != self.last_tid:
+                return 0
+            if self._new_flag:
+                self._new_flag = False
+                if os.read(self._new_pipe[0], 2) != '\0':
+                    raise RuntimeError
+        t = time()
+        select(self._new_pipe[:1], (), (), timeout)
+        return time() - t
+
+    transform_record_data = untransform_record_data = None
+
+
+class Object(object):
+
+    __slots__ = 'referrers', 'referents', 'prev_orphan', 'next_orphan'
+
+    def __init__(self, oid, referrers=(), referents=(),
+                 prev_orphan=None, next_orphan=None):
+        self.referrers = [p64(oid + i) for i in referrers]
+        self.referents = {p64(oid + i) for i in referents}
+        self.prev_orphan = None if prev_orphan is None else \
+            p64(oid + prev_orphan)
+        self.next_orphan = None if next_orphan is None else \
+            p64(oid + next_orphan)
+
+    def maybeOrphan(self):
+        return self.referents.issuperset(self.referrers)
+
+    def __repr__(self):
+        return '<%s%s>' % (self.__class__.__name__, ' '.join(
+            '%s=%r' % (attr, getattr(self, attr))
+            for attr in self.__slots__))
+
+
+class Changeset(object):
+
+    def __init__(self, storage, bootstrap=None):
+        self.storage = storage
+        self._load = storage.load
+        self.buckets = buckets = {}
+        bucket = self._get(z64)
+        if buckets[z64][0] is None:
+            bucket['__reflink_version__'] = VERSION
+            self._bootstrap = None
+        else:
+            version = bucket.get('__reflink_version__')
+            if version != VERSION:
+                raise Exception("unsupported reflink DB version %r"
+                                " (expected %r)" % (version, VERSION))
+            self._bootstrap = bucket.get('__reflink_bootstrap__')
+            if bootstrap is None:
+                buckets.clear()
+            elif self._bootstrap is None or self._bootstrap[1] != 0:
+                raise Exception("can not bootstrap: DB is not empty")
+        if bootstrap is not None:
+            checkAPI(storage)
+            self.bootstrap = bootstrap, 0
+        if self._bootstrap:
+            self.deleted = set()
+        self._last_gc = bucket.get('__reflink_last_gc__', z64)
+        self._last_pack = bucket.get('__reflink_last_pack__', z64)
+        self._pack = None
+        self.check_orphan = {}
+
+    @partial(property, attrgetter('_last_gc'))
+    def last_gc(self, value):
+        self._last_gc = self._get(z64)['__reflink_last_gc__'] = value
+
+    def pack(self, tid):
+        self.storage.app.setPackOrder.__call__ # check non-standard API
+        if self._last_pack < tid:
+            self._pack = tid
+
+    @partial(property, attrgetter('_bootstrap'))
+    def bootstrap(self, value):
+        self._bootstrap = value
+        bucket = self._get(z64)
+        if value is None:
+            del bucket['__reflink_bootstrap__'], self.deleted
+        else:
+            bucket['__reflink_bootstrap__'] = value
+
+    def abort(self):
+        self.buckets.clear()
+        self.check_orphan.clear()
+        assert not (self._bootstrap and self.deleted)
+
+    def _get(self, oid):
+        try:
+            return self.buckets[oid][2]
+        except KeyError:
+            try:
+                orig, serial = self._load(oid)
+            except POSKeyError:
+                bucket = {}
+                self.buckets[oid] = None, z64, bucket
+            else:
+                bucket = loads(orig)
+                self.buckets[oid] = orig, serial, bucket
+        return bucket
+
+    def get(self, oid):
+        bucket = self._get(b'\0' + oid[:-1])
+        key = ord(oid[-1]) # Py3
+        obj = bucket.get(key, ())
+        if not isinstance(obj, Object):
+            obj = bucket[key] = Object(u64(oid), *obj)
+        if oid not in self.check_orphan and self._bootstrap is None:
+            self.check_orphan[oid] =  not (
+                obj.prev_orphan or obj.maybeOrphan())
+        return obj
+
+    def commit(self, tid, info=''):
+        storage = self.storage
+        logger.info('commit @ %x (%s)', u64(tid), info or
+            'Δ %s' % timedelta(0, time() - TimeStamp(tid).timeTime()))
+        buckets = self.buckets
+        txn = TransactionMetaData()
+        storage.tpc_begin(txn, tid)
+        def shortenVal(i):
+            if i:
+                return u64(i) - oid
+        def shortenSeq(l):
+            return tuple(u64(i) - oid for i in l)
+        def shortenObj(x):
+            if v[-1] == x:
+                del v[-1]
+                return True
+        bootstrap = self._bootstrap
+        pack = self._pack
+        if bootstrap:
+            deleted_remove = self.deleted.remove
+        elif pack:
+            self._pack = None
+            self._last_pack = self._get(z64)['__reflink_last_pack__'] = pack
+            storage.app.setPackOrder(txn, pack)
+        for bucket_oid, (orig, serial, bucket) in buckets.iteritems():
+            base_oid = u64(bucket_oid) << 8
+            data = {}
+            for k, v in bucket.iteritems():
+                if isinstance(v, Object):
+                    oid = base_oid + k
+                    v = [shortenSeq(v.referrers),
+                         shortenSeq(sorted(v.referents)),
+                         shortenVal(v.prev_orphan),
+                         shortenVal(v.next_orphan)]
+                    if (shortenObj(None) and shortenObj(None) and
+                        shortenObj(()) and shortenObj(())):
+                        if not bootstrap:
+                            continue
+                        try:
+                            deleted_remove(p64(oid))
+                            continue
+                        except KeyError:
+                            pass
+                    v = tuple(v)
+                data[k] = v
+            if data:
+                data = dumps(data)
+                if orig != data:
+                    storage.store(bucket_oid, serial, data, '', txn)
+            elif orig:
+                storage.deleteObject(bucket_oid, serial, txn)
+        if bootstrap and self.deleted:
+            logger.warning(
+                "  %s already deleted OIDs will still be considered during the"
+                " final full GC of the bootstrap phase.", len(self.deleted))
+            self.deleted.clear()
+        storage.tpc_vote(txn)
+        storage.tpc_finish(txn)
+        buckets.clear()
+
+    def dump(self, tid):
+        checkAPI(self.storage)
+        buckets = self.buckets
+        bootstrap = self._bootstrap
+        assert not (buckets or self.check_orphan)
+        try:
+            if bootstrap is None:
+                self._bootstrap = True
+            with self.historical(tid):
+                for oid in self.storage.app.oids(tid):
+                    try:
+                        bucket = self._get(oid)
+                        oid = u64(oid) << 8
+                        if not oid:
+                            for x in sorted(x for x in bucket
+                                              if type(x) is str):
+                                print(x, repr(bucket.pop(x)))
+                        for x in sorted(bucket):
+                            x += oid
+                            obj = self.get(p64(x))
+                            print(x,
+                                map(u64, obj.referrers),
+                                map(u64, obj.referents),
+                                obj.prev_orphan and u64(obj.prev_orphan),
+                                obj.next_orphan and u64(obj.next_orphan))
+                    finally:
+                        buckets.clear()
+        finally:
+            self._bootstrap = bootstrap
+            assert not (buckets or self.check_orphan)
+
+    @contextmanager
+    def historical(self, tid):
+        if tid is None:
+            yield
+            return
+        assert not (self.buckets or self.check_orphan)
+        storage = self.storage
+        load = partial(storage.loadBefore, tid=inc64(tid))
+        try:
+            self._load = lambda oid: load(oid)[:2]
+            yield
+        finally:
+            self._load = storage.load
+            self.abort()
+
+    def full(self, tid):
+        with self.historical(tid):
+            import sqlite3
+            db = sqlite3.connect(':memory:', check_same_thread=False)
+            try:
+                db.text_factory = bytes
+                q = db.execute
+                q('CREATE TABLE t (oid INTEGER PRIMARY KEY, referents BLOB)')
+                count = 0
+                for oid in self.storage.app.oids(tid):
+                    x = u64(oid) << 8
+                    for k, v in loads(self._load(oid)[0]).iteritems():
+                        if isinstance(k, int):
+                            q('INSERT INTO t VALUES(?,?)', (x+k,
+                                dumps(v[1]) if len(v) > 1 and v[1] else None))
+                            count += 1
+                    db.commit()
+                logger.info("  #oids: %s", count)
+                stack = [0]
+                x = xrange(256)
+                while True:
+                    for v in x:
+                        try:
+                            oid = stack.pop()
+                        except IndexError:
+                            return {p64(*x) for x in q('SELECT oid FROM t')}
+                        k = oid,
+                        try:
+                            (v,), = q('SELECT referents FROM t WHERE oid=?', k)
+                        except ValueError:
+                            continue
+                        q('DELETE FROM t WHERE oid=?', k)
+                        if v:
+                            stack += map(oid.__add__, loads(v))
+                    db.commit()
+            finally:
+                db.close()
+
+    @property
+    def orphan(self):
+        buckets = self.buckets
+        empty = not buckets
+        root = self.get(z64)
+        if empty:
+            buckets.clear()
+        self.check_orphan.clear()
+        return root.next_orphan
+
+    def orphans(self, tid):
+        with self.historical(tid):
+            get = self.get
+            orphans = set()
+            check_orphan = set()
+            check_cycle = []
+            keep = {}
+            obj = self.get(z64)
+            if __debug__:
+                seen = set()
+            while True:
+                oid = obj.next_orphan
+                if not oid:
+                    break
+                if __debug__:
+                    assert oid not in seen, u64(oid)
+                    seen.add(oid)
+                obj = get(oid)
+                if obj.referrers:
+                    assert obj.maybeOrphan(), (oid, obj.referrers)
+                    check_cycle.append((oid, obj))
+                else:
+                    orphans.add(oid)
+                    check_orphan |= obj.referents
+            while check_orphan:
+                oid = check_orphan.pop()
+                obj = get(oid)
+                if orphans.issuperset(obj.referrers):
+                    orphans.add(oid)
+                    check_orphan |= obj.referents
+                else:
+                    check_cycle.append((oid, obj))
+            while check_cycle:
+                oid, obj = check_cycle.pop()
+                check_orphan = []
+                cycle = {oid}
+                x = obj
+                while True:
+                    referrers = set(x.referrers) - cycle - orphans
+                    x = x.referents - cycle - orphans
+                    if not referrers.issubset(x):
+                        # not a simple cycle, give up
+                        if obj.prev_orphan:
+                            keep[oid] = obj
+                        break
+                    check_orphan += x
+                    cycle |= x
+                    try:
+                        x = get(check_orphan.pop())
+                    except IndexError:
+                        orphans |= cycle
+                        break
+            x = [u64(oid) for oid in keep if self.path(oid)[-1] != z64]
+        if keep:
+            if x:
+                logger.error(
+                    "It looks like the following oids can be"
+                    " garbage-collected: %s. Please report.",
+                    ','.join(map('%x'.__mod__, x)))
+            for obj in keep.itervalues():
+                self.keep(obj)
+        return orphans
+
+    def keep(self, obj):
+        prev = obj.prev_orphan
+        obj.prev_orphan = None
+        oid = self.get(prev).next_orphan = obj.next_orphan
+        if oid:
+            obj.next_orphan = None
+            self.get(oid).prev_orphan = prev
+
+    def path(self, oid):
+        orphan = []
+        path = []
+        stack = []
+        x = iter((oid,))
+        while True:
+            try:
+                oid = next(x)
+            except StopIteration:
+                if len(orphan) < len(path):
+                    orphan = path[:]
+                try:
+                    x = stack.pop()
+                except IndexError:
+                    return orphan
+                del path[-1]
+            else:
+                if oid in path:
+                    continue
+                path.append(oid)
+                if oid == z64:
+                    return path
+                stack.append(x)
+                x = iter(self.get(oid).referrers)
+
+
+class ArgumentDefaultsHelpFormatter(argparse.HelpFormatter):
+
+    def _format_action(self, action):
+        if action.const is None is not action.default is not argparse.SUPPRESS:
+            default = '(default: %(default)s)'
+            help = action.help
+            if help:
+                if not help.endswith(default):
+                    action.help = help + ' ' + default
+            else:
+                action.help = default
+        return super(ArgumentDefaultsHelpFormatter, self)._format_action(action)
+
+
+def main(args=None):
+    if args is None:
+        args = sys.argv[1:]
+
+    kw = dict(formatter_class=ArgumentDefaultsHelpFormatter)
+    parser = argparse.ArgumentParser(
+        description="External ZODB GC by tracking references between OIDs and"
+                    " marking orphaned objects as deleted automatically.",
+        **kw)
+    _ = parser.add_argument
+    _('-v', '--verbose', action='store_true',
+        help="Verbose mode, display more information.")
+    _('refs', metavar="REFS_URI", help="ZODB containing tracking data."
+        " If the main DB is truncated, then this DB must be truncated at the"
+        " same TID. Packing this DB does not need any GC.")
+    parsers = parser.add_subparsers(dest='command')
+
+    def gc(jobs_help):
+        _ = s.add_argument
+        _('-f', '--full', action='store_true',
+            help="Always perform a full GC. This should only be used"
+                " occasionally, preferably with -n to only check"
+                " if a normal GC is enough.")
+        _('-j', '--jobs', type=int, metavar="N", default=1, help=jobs_help)
+        _('-n', '--dry-run', metavar="DUMP",
+            help="Save OIDs that would be deleted during a GC into the"
+                " specified file and exit. ERP5 uid is given in parentheses"
+                " if is exists. Both oid & uid are output in hexadecimal.")
+        _('main', metavar="MAIN_URI", help="ZODB to track.")
+    def period(default=0, extra_help=""):
+        s.add_argument(
+            '-p', '--period', type=float, metavar="SECONDS", default=default,
+            help="Age of the historical revision at which a GC is performed"
+                " (this can be seen as a grace period).%s This is mainly to"
+                " work around possible conflicts with undo: an orphan OID may"
+                " be referenced again by an undone transactions, requiring to"
+                " also undo GC transactions that happened after. So when this"
+                " argument is not 0, a GC calculates twice the list of OIDs to"
+                " delete, now and in the past, to exclude those that should be"
+                " kept." % extra_help)
+    tid_arg = dict(metavar="TID", type=eval, help="TID as Python integer.")
+
+    _ = parsers.add_parser('bootstrap',
+        help="By default, all transactions since the creation of main DB are"
+             " scanned. In the case where such history would take too long to"
+             " process, you can try this command so that the 'run' command"
+             " starts with 2 extra steps: scan the whole main DB at the given"
+             " TID and do a full GC. Both DB must provide a non-standard API"
+             " that only NEO is known to have.",
+        **kw).add_argument
+    _('tid', **tid_arg)
+
+    _ = parsers.add_parser('dump',
+        help="Dump the whole reflink DB to stdout.",
+        **kw).add_argument
+    _('tid', nargs='?', **tid_arg)
+
+    s = parsers.add_parser('gc',
+        help="Do a GC immediately, ignoring new transactions, and exit.",
+        **kw)
+    gc("Concurrent reads from main DB during GC.")
+    period()
+
+    _ = parsers.add_parser('path',
+        help="Get ancestors of an OID.",
+        **kw).add_argument
+    _('--tid', **tid_arg)
+    _('oid', metavar="OID", type=eval,
+        help="OID as Python integer.")
+    _('main', metavar="MAIN_URI", nargs='?',
+        help="Tracked ZODB, for class information.")
+
+    s = parsers.add_parser('run',
+        help="Track references and GC automatically. This is the main command."
+             " GCs are performed when there's no new transaction to process.",
+             **kw)
+    gc("Concurrent reads from main DB during bootstrap & GC.")
+    _ = s.add_mutually_exclusive_group().add_argument
+    _('-0', '--exit-before-gc', action='store_true',
+        help="Exit before a GC.")
+    _('-1', '--exit-after-gc', action='store_true',
+        help="Exit after a GC.")
+    _('-N', '--no-gc', action='store_true',
+        help="Only track references.")
+    _ = s.add_argument
+    _('-i', '--commit-interval', type=float, metavar="SECONDS", default=10,
+        help="Commit every SECONDS of work.")
+    _('--pack-neo', type=float, metavar="EPOCH",
+        help="Pack time in seconds since the epoch. This argument is ignored"
+             " during bootstrap and it is only to pack the refs DB when it is"
+             " run by NEO. Other IStorage implementations don't store pack"
+             " commands in transactions and pack() can be used as long as it's"
+             " done without GC.")
+    period(86400,
+        " For performance reasons, this revision won't be older than the"
+        " previous GC commit so GCs may be delayed this number of seconds.")
+
+    args = parser.parse_args(args)
+
+    handler = logging.StreamHandler()
+    handler.setFormatter(logging.Formatter(
+        '%(asctime)s.%(msecs)03u %(levelname)-9s %(message)s',
+        '%Y-%m-%d %H:%M:%S'))
+    logging.getLogger().addHandler(handler)
+    if args.verbose:
+        logger.setLevel(logging.INFO)
+
+    command = args.command
+    bootstrap = command == "bootstrap"
+    changeset = Changeset(openStorage(args.refs),
+                          args.tid if bootstrap else None)
+
+    if command == "dump":
+        tid = args.tid
+        changeset.dump(None if tid is None else p64(tid))
+        return
+
+    tid = changeset.storage.lastTransaction()
+
+    if bootstrap:
+        changeset.commit(inc64(tid))
+        print("Bootstrap at %s UTC. You can now use the 'run' command."
+              % TimeStamp(p64(args.tid)))
+        return
+
+    if args.main:
+        main_storage = openStorage(args.main)
+        for iface in (ZODB.interfaces.IStorageIteration,
+                      ZODB.interfaces.IExternalGC):
+            if not iface.providedBy(main_storage):
+                return "Main storage shall implement " + iface.__name__
+
+    if command == "path":
+        t = args.tid
+        if t is None:
+            tid = inc64(tid)
+        else:
+            tid = p64(t + 1)
+            t = p64(t)
+        def find_global(*args):
+            obj.extend(args)
+        with changeset.historical(t):
+            for oid in reversed(changeset.path(p64(args.oid))):
+                obj = [hex(u64(oid))]
+                if args.main:
+                    data = main_storage.loadBefore(oid, tid)[0]
+                    PersistentUnpickler(find_global, None,
+                                        BytesIO(data)).load()
+                print(*obj)
+        return
+
+    bootstrap = changeset.bootstrap
+    if command == 'gc':
+        if bootstrap and not (bootstrap[1] is None and args.dry_run):
+            return "can not GC: bootstrapping"
+        commit_interval = 0
+        exit_before_gc = no_gc = False
+        exit_after_gc = True
+    else:
+        assert command == "run", command
+        commit_interval = args.commit_interval
+        if commit_interval <= 0:
+            parser.error("--commit-interval must be strictly positive.")
+        exit_before_gc = args.exit_before_gc
+        exit_after_gc = args.exit_after_gc
+        no_gc = args.no_gc
+        t = args.pack_neo
+        if t:
+            changeset.pack(tidFromTime(t))
+    job_count = args.jobs
+    if job_count <= 0:
+        parser.error("--jobs must be strictly positive.")
+    period = args.period
+    if period < 0:
+        parser.error("--period must be positive.")
+
+    full = args.full
+    if full:
+        checkAPI(changeset.storage)
+
+    dry_run = args.dry_run
+    if dry_run:
+        dry_run_stats = defaultdict(list)
+        def find_global(*args):
+            dry_run_stats[args].append(oid)
+        uid_dict = {}
+        load_broken = lambda *args: Broken
+        load_persistent = lambda *args: None
+
+    del args, command, parser
+
+    queue = Queue(3)
+    exc_info = [] # Py3
+    def checkExc():
+        if exc_info:
+            etype, value, tb = exc_info
+            raise etype, value, tb
+
+    if bootstrap and bootstrap[1] is not None:
+        @apply
+        def next_oid():
+            tid, oid = map(p64, bootstrap)
+            load = partial(main_storage.loadBefore, tid=inc64(tid))
+            iter_oids = main_storage.app.oids(tid, oid)
+            if job_count == 1:
+                def loadThread():
+                    put = queue.put
+                    try:
+                        for oid in iter_oids:
+                            put((oid, load(oid)[0]))
+                    except:
+                        exc_info[:] = sys.exc_info()
+                    put(None)
+                t = threading.Thread(target=loadThread)
+                t.daemon = True
+                t.start()
+                return queue.get
+            job_queue = Queue(2 * job_count)
+            Lock = threading.Lock
+            def loadThread(iter_lock=Lock(), put=job_queue.put):
+                try:
+                    while True:
+                        l = Lock()
+                        with l:
+                            with iter_lock:
+                                if exc_info:
+                                    return
+                                oid = next(iter_oids)
+                                r = [oid, None, l]
+                                put(r)
+                            r[1] = load(oid)[0]
+                except StopIteration:
+                    pass
+                except:
+                    exc_info[:] = sys.exc_info()
+                put(None)
+            for t in xrange(job_count):
+                t = threading.Thread(target=loadThread)
+                t.daemon = True
+                t.start()
+            def next_oid(get=job_queue.get):
+                r = get()
+                if r:
+                    r[2].acquire()
+                    return r[:2]
+            return next_oid
+        next_commit = time() + commit_interval
+        while True:
+            r = next_oid()
+            if r is None:
+                checkExc()
+                break
+            oid, data = r
+            try:
+                referents = set(referencesf(data))
+            except Exception:
+                logger.warning("Corrupted record %x@%x", u64(oid), bootstrap[0])
+                referents = set()
+            else:
+                referents.discard(oid)
+            src = changeset.get(oid)
+            src.referents = referents
+            for referent in referents:
+                insort(changeset.get(referent).referrers, oid)
+            t = time()
+            if next_commit <= t:
+                tid = inc64(tid)
+                changeset.bootstrap = bootstrap[0], u64(oid) + 1
+                changeset.commit(tid, "oid=%x" % u64(oid))
+                next_commit = t + commit_interval
+        changeset.bootstrap = bootstrap[0], None
+        tid = p64(bootstrap[0])
+        changeset.commit(tid)
+        del next_oid
+
+    if job_count == 1:
+        def iter_orphans(iter_oids, load):
+            for i, oid in iter_oids:
+                try:
+                    data, serial = load(oid)
+                except POSKeyError:
+                    continue
+                yield i, oid, data, serial
+    else:
+        def iter_orphans(iter_oids, load):
+            job_queue = Queue(2 * job_count)
+            Lock = threading.Lock
+            def loadThread(iter_lock=Lock(),
+                           put=job_queue.put):
+                try:
+                    while True:
+                        l = Lock()
+                        with l:
+                            with iter_lock:
+                                if exc_info:
+                                    return
+                                i, oid = next(iter_oids)
+                                r = [l, i, oid]
+                                put(r)
+                            try:
+                                r += load(oid)
+                            except POSKeyError:
+                                pass
+                except StopIteration:
+                    pass
+                except:
+                    exc_info[:] = sys.exc_info()
+                put(None)
+            threads = []
+            try:
+                for t in xrange(job_count):
+                    t = threading.Thread(target=loadThread)
+                    t.daemon = True
+                    t.start()
+                    threads.append(t)
+                get = job_queue.get
+                while True:
+                    r = get()
+                    if r is None:
+                        break
+                    r[0].acquire()
+                    if len(r) != 3:
+                        yield r[1:]
+            finally:
+                iter_oids = iter(())
+                try:
+                    while True:
+                        get(False)
+                except Empty:
+                    pass
+                for t in threads:
+                    t.join()
+            checkExc()
+
+    invalidation_listener = InvalidationListener(main_storage, tid)
+
+    def iterTrans(x):
+        put = queue.put
+        try:
+            for x in x:
+                put(x)
+                for x in x:
+                    put(x)
+                put(None)
+        except:
+            exc_info[:] = sys.exc_info()
+        put(None)
+
+    next_gc = period and TimeStamp(changeset.last_gc).timeTime() + period
+    next_commit = time() + commit_interval
+    while True:
+        if commit_interval:
+            thread = threading.Thread(target=iterTrans,
+                args=(main_storage.iterator(inc64(tid)),))
+            thread.daemon = True
+            thread.start()
+            while True:
+                t = queue.get()
+                if t is None:
+                    checkExc()
+                    break
+                tid = t.tid
+                # logger.debug("tid=%x", u64(tid))
+                check_orphan = {}
+                while True:
+                    record = queue.get()
+                    if record is None:
+                        checkExc()
+                        break
+                    oid = record.oid
+                    # logger.debug("  oid=%x", u64(oid))
+                    src = changeset.get(oid)
+                    data = record.data
+                    prev_set = src.referents
+                    if data is None:
+                        # logger.debug("    deleted")
+                        if src.prev_orphan:
+                            changeset.keep(src)
+                        else:
+                            if bootstrap:
+                                changeset.deleted.add(oid)
+                            if check_orphan.pop(oid, None) is None:
+                                changeset.check_orphan[oid] = False
+                        new_set = set()
+                    else:
+                        if not (src.prev_orphan or prev_set or src.referrers
+                                or oid == z64 or bootstrap):
+                            # After a pack, an oid may be
+                            # orphan from its creation.
+                            check_orphan[oid] = src
+                        try:
+                            new_set = set(referencesf(data))
+                        except Exception:
+                            logger.warning("Corrupted record %x@%x",
+                                           u64(oid), u64(tid))
+                            new_set = set()
+                        else:
+                            new_set.discard(oid)
+                    if new_set == prev_set:
+                        continue
+                    src.referents = new_set
+                    for referent in new_set - prev_set:
+                        # logger.debug("  + %x", u64(referent))
+                        dst = changeset.get(referent)
+                        insort(dst.referrers, oid)
+                        if dst.prev_orphan:
+                            changeset.keep(dst)
+                    prev_set.difference_update(new_set)
+                    for referent in prev_set:
+                        # logger.debug("  - %x", u64(referent))
+                        dst = changeset.get(referent)
+                        dst.referrers.remove(oid)
+                        if changeset.check_orphan.get(referent):
+                            changeset.check_orphan[referent] = False
+                            check_orphan[referent] = dst
+                t = inc64(tid)
+                for oid, obj in check_orphan.iteritems():
+                    if obj.maybeOrphan():
+                        assert not (obj.prev_orphan or obj.next_orphan), oid
+                        if not obj.referents:
+                            try:
+                                if main_storage.loadBefore(oid, t) is None:
+                                    continue
+                            except POSKeyError:
+                                continue
+                        obj.prev_orphan = z64
+                        prev_orphan = changeset.get(z64)
+                        next_orphan = prev_orphan.next_orphan
+                        if next_orphan:
+                            changeset.get(next_orphan).prev_orphan = oid
+                            obj.next_orphan = next_orphan
+                        prev_orphan.next_orphan = oid
+                changeset.check_orphan.clear()
+
+                t = time()
+                if next_commit <= t:
+                    changeset.commit(tid)
+                    next_commit = t + commit_interval
+            thread.join()
+
+        t = time()
+        timeout = next_gc - t
+        if timeout <= 0 or not commit_interval:
+            timeout = None
+            if (full or changeset.orphan or bootstrap) and not no_gc:
+                if changeset.buckets:
+                    next_commit = t + commit_interval
+                    changeset.commit(tid)
+                assert tid == changeset.storage.lastTransaction()
+                if exit_before_gc:
+                    break
+                if full or bootstrap:
+                    logger.info('Full GC...')
+                    gc = changeset.full
+                else:
+                    logger.info('Incremental GC...')
+                    gc = changeset.orphans
+                gc_tid = tid if bootstrap or not period else \
+                    tidFromTime(time() - period)
+                if gc_tid < tid:
+                    if gc_tid < changeset.last_gc:
+                        logger.warning(
+                            "Doing GC at a TID (0x%x) older than"
+                            " the previous one (0x%x)",
+                            u64(gc_tid), u64(changeset.last_gc))
+                    orphans = gc(gc_tid)
+                    if orphans:
+                        changeset.abort()
+                        x = gc(None)
+                        orphans &= x
+                        if x and not orphans:
+                            next_gc = TimeStamp(tid).timeTime() + period
+                            timeout = max(0, next_gc - time())
+                        del x
+                else:
+                    gc_tid = tid
+                    orphans = gc(None)
+                orphans = sorted(orphans)
+                logger.info('  found %s OID(s) to delete', len(orphans))
+                count = 0
+                while orphans:
+                    txn = TransactionMetaData(
+                        description=TXN_GC_DESC % u64(gc_tid))
+                    main_storage.tpc_begin(txn)
+                    try:
+                        for i, oid, data, serial in iter_orphans(
+                                enumerate(orphans), main_storage.load):
+                            if gc_tid < serial:
+                                count = None
+                                break
+                            main_storage.deleteObject(oid, serial, txn)
+                            if dry_run:
+                                oid = u64(oid)
+                                try:
+                                    x = PersistentUnpickler(find_global,
+                                        load_persistent, BytesIO(data))
+                                    x.load()
+                                except Exception:
+                                    assert data is not None, oid
+                                    dry_run_stats[
+                                        ('corrupted',) if data else ('empty',)
+                                        ].append(oid)
+                                else:
+                                    x.find_global = load_broken
+                                    try:
+                                        uid_dict[oid] = x.load()['uid']
+                                    except Exception:
+                                        pass
+                            count += 1
+                            if count == 0x1fffff: # MySQL limitation (MEDIUMBLOB)
+                                del orphans[:i]
+                                break
+                        else:
+                            orphans = None
+                        if count:
+                            logger.info('  tpc_vote (%s delete(s))...', count)
+                            main_storage.tpc_vote(txn)
+                            if dry_run:
+                                count = None
+                                with os.fdopen(os.open(dry_run,
+                                        os.O_WRONLY | os.O_CREAT | os.O_EXCL, # Py3
+                                        0o666), 'w') as f:
+                                    for x in sorted(dry_run_stats):
+                                        y = []
+                                        for oid in dry_run_stats.pop(x):
+                                            uid = uid_dict.get(oid)
+                                            y.append(
+                                                '%x' % oid if uid is None else
+                                                '%x(%x)' % (oid, uid))
+                                        print(len(y), '.'.join(x), *y,
+                                              sep=',', file=f)
+                                return
+                            logger.info('  tpc_finish...')
+                            main_storage.tpc_finish(txn,
+                                invalidation_listener.tpc_finish)
+                            changeset.last_gc = invalidation_listener.last_gc
+                            next_commit = 0
+                            if period:
+                                # We don't want future `gc(gc_tid)` to waste
+                                # time with OIDs that are already deleted.
+                                next_gc = TimeStamp(changeset.last_gc
+                                                    ).timeTime() + period
+                            continue
+                    except ConflictError:
+                        count = None
+                    finally:
+                        if count:
+                            count = 0
+                        else:
+                            main_storage.tpc_abort(txn)
+                    break
+                del orphans
+                if count == 0:
+                    if bootstrap:
+                        bootstrap = changeset.bootstrap = None
+                        logger.info("Bootstrap completed")
+                        next_commit = 0
+                    if exit_after_gc:
+                        break
+            if not commit_interval:
+                break
+
+        next_commit += invalidation_listener.wait(tid, timeout)
+
+
+if __name__ == '__main__':
+    sys.exit(main())