src/allmydata/test/test_checker.py

   1
   2 import simplejson
   3 import os.path, shutil
   4 from twisted.trial import unittest
   5 from twisted.internet import defer
   6 from allmydata import check_results, uri
   7 from allmydata import uri as tahoe_uri
   8 from allmydata.util import base32
   9 from allmydata.web import check_results as web_check_results
  10 from allmydata.storage_client import StorageFarmBroker, NativeStorageServer
  11 from allmydata.storage.server import storage_index_to_dir
  12 from allmydata.monitor import Monitor
  13 from allmydata.test.no_network import GridTestMixin
  14 from allmydata.immutable.upload import Data
  15 from allmydata.test.common_web import WebRenderingMixin
  16 from allmydata.mutable.publish import MutableData
  17
  18 class FakeClient:
  19     def get_storage_broker(self):
  20         return self.storage_broker
  21
  22 class WebResultsRendering(unittest.TestCase, WebRenderingMixin):
  23
  24     def create_fake_client(self):
  25         sb = StorageFarmBroker(None, True)
  26         # s.get_name() (the "short description") will be "v0-00000000".
  27         # s.get_longname() will include the -long suffix.
  28         # s.get_peerid() (i.e. tubid) will be "aaa.." or "777.." or "ceir.."
  29         servers = [("v0-00000000-long", "\x00"*20, "peer-0"),
  30                    ("v0-ffffffff-long", "\xff"*20, "peer-f"),
  31                    ("v0-11111111-long", "\x11"*20, "peer-11")]
  32         for (key_s, peerid, nickname) in servers:
  33             tubid_b32 = base32.b2a(peerid)
  34             furl = "pb://%s@nowhere/fake" % tubid_b32
  35             ann = { "version": 0,
  36                     "service-name": "storage",
  37                     "anonymous-storage-FURL": furl,
  38                     "permutation-seed-base32": "",
  39                     "nickname": unicode(nickname),
  40                     "app-versions": {}, # need #466 and v2 introducer
  41                     "my-version": "ver",
  42                     "oldest-supported": "oldest",
  43                     }
  44             s = NativeStorageServer(key_s, ann)
  45             sb.test_add_server(peerid, s) # XXX: maybe use key_s?
  46         c = FakeClient()
  47         c.storage_broker = sb
  48         return c
  49
  50     def render_json(self, page):
  51         d = self.render1(page, args={"output": ["json"]})
  52         return d
  53
  54     def test_literal(self):
  55         c = self.create_fake_client()
  56         lcr = web_check_results.LiteralCheckResultsRenderer(c)
  57
  58         d = self.render1(lcr)
  59         def _check(html):
  60             s = self.remove_tags(html)
  61             self.failUnlessIn("Literal files are always healthy", s)
  62         d.addCallback(_check)
  63         d.addCallback(lambda ignored:
  64                       self.render1(lcr, args={"return_to": ["FOOURL"]}))
  65         def _check_return_to(html):
  66             s = self.remove_tags(html)
  67             self.failUnlessIn("Literal files are always healthy", s)
  68             self.failUnlessIn('<a href="FOOURL">Return to file.</a>',
  69                               html)
  70         d.addCallback(_check_return_to)
  71         d.addCallback(lambda ignored: self.render_json(lcr))
  72         def _check_json(json):
  73             j = simplejson.loads(json)
  74             self.failUnlessEqual(j["storage-index"], "")
  75             self.failUnlessEqual(j["results"]["healthy"], True)
  76         d.addCallback(_check_json)
  77         return d
  78
  79     def test_check(self):
  80         c = self.create_fake_client()
  81         sb = c.storage_broker
  82         serverid_1 = "\x00"*20
  83         serverid_f = "\xff"*20
  84         server_1 = sb.get_stub_server(serverid_1)
  85         server_f = sb.get_stub_server(serverid_f)
  86         u = uri.CHKFileURI("\x00"*16, "\x00"*32, 3, 10, 1234)
  87         data = { "count_shares_needed": 3,
  88                  "count_shares_expected": 9,
  89                  "count_shares_good": 10,
  90                  "count_good_share_hosts": 11,
  91                  "count_recoverable_versions": 1,
  92                  "count_unrecoverable_versions": 0,
  93                  "servers_responding": [],
  94                  "sharemap": {"shareid1": [server_1, server_f]},
  95                  "count_wrong_shares": 0,
  96                  "list_corrupt_shares": [],
  97                  "count_corrupt_shares": 0,
  98                  "list_incompatible_shares": [],
  99                  "count_incompatible_shares": 0,
 100                  "report": [], "share_problems": [], "servermap": None,
 101                  }
 102         cr = check_results.CheckResults(u, u.get_storage_index(),
 103                                         healthy=True, recoverable=True,
 104                                         needs_rebalancing=False,
 105                                         summary="groovy",
 106                                         **data)
 107         w = web_check_results.CheckResultsRenderer(c, cr)
 108         html = self.render2(w)
 109         s = self.remove_tags(html)
 110         self.failUnlessIn("File Check Results for SI=2k6avp", s) # abbreviated
 111         self.failUnlessIn("Healthy : groovy", s)
 112         self.failUnlessIn("Share Counts: need 3-of-9, have 10", s)
 113         self.failUnlessIn("Hosts with good shares: 11", s)
 114         self.failUnlessIn("Corrupt shares: none", s)
 115         self.failUnlessIn("Wrong Shares: 0", s)
 116         self.failUnlessIn("Recoverable Versions: 1", s)
 117         self.failUnlessIn("Unrecoverable Versions: 0", s)
 118         self.failUnlessIn("Good Shares (sorted in share order): Share ID Nickname Node ID shareid1 peer-0 00000000 peer-f ffffffff", s)
 119
 120         cr = check_results.CheckResults(u, u.get_storage_index(),
 121                                         healthy=False, recoverable=True,
 122                                         needs_rebalancing=False,
 123                                         summary="ungroovy",
 124                                         **data)
 125         w = web_check_results.CheckResultsRenderer(c, cr)
 126         html = self.render2(w)
 127         s = self.remove_tags(html)
 128         self.failUnlessIn("File Check Results for SI=2k6avp", s) # abbreviated
 129         self.failUnlessIn("Not Healthy! : ungroovy", s)
 130
 131         data["count_corrupt_shares"] = 1
 132         data["list_corrupt_shares"] = [(server_1, u.get_storage_index(), 2)]
 133         cr = check_results.CheckResults(u, u.get_storage_index(),
 134                                         healthy=False, recoverable=False,
 135                                         needs_rebalancing=False,
 136                                         summary="rather dead",
 137                                         **data)
 138         w = web_check_results.CheckResultsRenderer(c, cr)
 139         html = self.render2(w)
 140         s = self.remove_tags(html)
 141         self.failUnlessIn("File Check Results for SI=2k6avp", s) # abbreviated
 142         self.failUnlessIn("Not Recoverable! : rather dead", s)
 143         self.failUnlessIn("Corrupt shares: Share ID Nickname Node ID sh#2 peer-0 00000000", s)
 144
 145         html = self.render2(w)
 146         s = self.remove_tags(html)
 147         self.failUnlessIn("File Check Results for SI=2k6avp", s) # abbreviated
 148         self.failUnlessIn("Not Recoverable! : rather dead", s)
 149
 150         html = self.render2(w, args={"return_to": ["FOOURL"]})
 151         self.failUnlessIn('<a href="FOOURL">Return to file/directory.</a>',
 152                           html)
 153
 154         d = self.render_json(w)
 155         def _check_json(jdata):
 156             j = simplejson.loads(jdata)
 157             self.failUnlessEqual(j["summary"], "rather dead")
 158             self.failUnlessEqual(j["storage-index"],
 159                                  "2k6avpjga3dho3zsjo6nnkt7n4")
 160             expected = {'needs-rebalancing': False,
 161                         'count-shares-expected': 9,
 162                         'healthy': False,
 163                         'count-unrecoverable-versions': 0,
 164                         'count-shares-needed': 3,
 165                         'sharemap': {"shareid1":
 166                                      ["v0-00000000-long", "v0-ffffffff-long"]},
 167                         'count-recoverable-versions': 1,
 168                         'list-corrupt-shares':
 169                         [["v0-00000000-long", "2k6avpjga3dho3zsjo6nnkt7n4", 2]],
 170                         'count-good-share-hosts': 11,
 171                         'count-wrong-shares': 0,
 172                         'count-shares-good': 10,
 173                         'count-corrupt-shares': 1,
 174                         'servers-responding': [],
 175                         'recoverable': False,
 176                         }
 177             self.failUnlessEqual(j["results"], expected)
 178         d.addCallback(_check_json)
 179         d.addCallback(lambda ignored: self.render1(w))
 180         def _check(html):
 181             s = self.remove_tags(html)
 182             self.failUnlessIn("File Check Results for SI=2k6avp", s)
 183             self.failUnlessIn("Not Recoverable! : rather dead", s)
 184         d.addCallback(_check)
 185         return d
 186
 187
 188     def test_check_and_repair(self):
 189         c = self.create_fake_client()
 190         sb = c.storage_broker
 191         serverid_1 = "\x00"*20
 192         serverid_f = "\xff"*20
 193         u = uri.CHKFileURI("\x00"*16, "\x00"*32, 3, 10, 1234)
 194
 195         data = { "count_shares_needed": 3,
 196                  "count_shares_expected": 10,
 197                  "count_shares_good": 6,
 198                  "count_good_share_hosts": 7,
 199                  "count_recoverable_versions": 1,
 200                  "count_unrecoverable_versions": 0,
 201                  "servers_responding": [],
 202                  "sharemap": {"shareid1": [sb.get_stub_server(serverid_1),
 203                                            sb.get_stub_server(serverid_f)]},
 204                  "count_wrong_shares": 0,
 205                  "list_corrupt_shares": [],
 206                  "count_corrupt_shares": 0,
 207                  "list_incompatible_shares": [],
 208                  "count_incompatible_shares": 0,
 209                  "report": [], "share_problems": [], "servermap": None,
 210                  }
 211         pre_cr = check_results.CheckResults(u, u.get_storage_index(),
 212                                             healthy=False, recoverable=True,
 213                                             needs_rebalancing=False,
 214                                             summary="illing",
 215                                             **data)
 216
 217         data = { "count_shares_needed": 3,
 218                  "count_shares_expected": 10,
 219                  "count_shares_good": 10,
 220                  "count_good_share_hosts": 11,
 221                  "count_recoverable_versions": 1,
 222                  "count_unrecoverable_versions": 0,
 223                  "servers_responding": [],
 224                  "sharemap": {"shareid1": [sb.get_stub_server(serverid_1),
 225                                            sb.get_stub_server(serverid_f)]},
 226                  "count_wrong_shares": 0,
 227                  "count_corrupt_shares": 0,
 228                  "list_corrupt_shares": [],
 229                  "list_incompatible_shares": [],
 230                  "count_incompatible_shares": 0,
 231                  "report": [], "share_problems": [], "servermap": None,
 232                  }
 233         post_cr = check_results.CheckResults(u, u.get_storage_index(),
 234                                              healthy=True, recoverable=True,
 235                                              needs_rebalancing=False,
 236                                              summary="groovy",
 237                                              **data)
 238
 239         crr = check_results.CheckAndRepairResults(u.get_storage_index())
 240         crr.pre_repair_results = pre_cr
 241         crr.post_repair_results = post_cr
 242         crr.repair_attempted = False
 243
 244         w = web_check_results.CheckAndRepairResultsRenderer(c, crr)
 245         html = self.render2(w)
 246         s = self.remove_tags(html)
 247
 248         self.failUnlessIn("File Check-And-Repair Results for SI=2k6avp", s)
 249         self.failUnlessIn("Healthy : groovy", s)
 250         self.failUnlessIn("No repair necessary", s)
 251         self.failUnlessIn("Post-Repair Checker Results:", s)
 252         self.failUnlessIn("Share Counts: need 3-of-10, have 10", s)
 253
 254         crr.repair_attempted = True
 255         crr.repair_successful = True
 256         html = self.render2(w)
 257         s = self.remove_tags(html)
 258
 259         self.failUnlessIn("File Check-And-Repair Results for SI=2k6avp", s)
 260         self.failUnlessIn("Healthy : groovy", s)
 261         self.failUnlessIn("Repair successful", s)
 262         self.failUnlessIn("Post-Repair Checker Results:", s)
 263
 264         crr.repair_attempted = True
 265         crr.repair_successful = False
 266         post_cr = check_results.CheckResults(u, u.get_storage_index(),
 267                                              healthy=False, recoverable=True,
 268                                              needs_rebalancing=False,
 269                                              summary="better",
 270                                              **data)
 271         crr.post_repair_results = post_cr
 272         html = self.render2(w)
 273         s = self.remove_tags(html)
 274
 275         self.failUnlessIn("File Check-And-Repair Results for SI=2k6avp", s)
 276         self.failUnlessIn("Not Healthy! : better", s)
 277         self.failUnlessIn("Repair unsuccessful", s)
 278         self.failUnlessIn("Post-Repair Checker Results:", s)
 279
 280         crr.repair_attempted = True
 281         crr.repair_successful = False
 282         post_cr = check_results.CheckResults(u, u.get_storage_index(),
 283                                              healthy=False, recoverable=False,
 284                                              needs_rebalancing=False,
 285                                              summary="worse",
 286                                              **data)
 287         crr.post_repair_results = post_cr
 288         html = self.render2(w)
 289         s = self.remove_tags(html)
 290
 291         self.failUnlessIn("File Check-And-Repair Results for SI=2k6avp", s)
 292         self.failUnlessIn("Not Recoverable! : worse", s)
 293         self.failUnlessIn("Repair unsuccessful", s)
 294         self.failUnlessIn("Post-Repair Checker Results:", s)
 295
 296         d = self.render_json(w)
 297         def _got_json(data):
 298             j = simplejson.loads(data)
 299             self.failUnlessEqual(j["repair-attempted"], True)
 300             self.failUnlessEqual(j["storage-index"],
 301                                  "2k6avpjga3dho3zsjo6nnkt7n4")
 302             self.failUnlessEqual(j["pre-repair-results"]["summary"], "illing")
 303             self.failUnlessEqual(j["post-repair-results"]["summary"], "worse")
 304         d.addCallback(_got_json)
 305
 306         w2 = web_check_results.CheckAndRepairResultsRenderer(c, None)
 307         d.addCallback(lambda ignored: self.render_json(w2))
 308         def _got_lit_results(data):
 309             j = simplejson.loads(data)
 310             self.failUnlessEqual(j["repair-attempted"], False)
 311             self.failUnlessEqual(j["storage-index"], "")
 312         d.addCallback(_got_lit_results)
 313         return d
 314
 315 class BalancingAct(GridTestMixin, unittest.TestCase):
 316     # test for #1115 regarding the 'count-good-share-hosts' metric
 317
 318
 319     def add_server(self, server_number, readonly=False):
 320         assert self.g, "I tried to find a grid at self.g, but failed"
 321         ss = self.g.make_server(server_number, readonly)
 322         #log.msg("just created a server, number: %s => %s" % (server_number, ss,))
 323         self.g.add_server(server_number, ss)
 324
 325     def add_server_with_share(self, server_number, uri, share_number=None,
 326                               readonly=False):
 327         self.add_server(server_number, readonly)
 328         if share_number is not None:
 329             self.copy_share_to_server(uri, share_number, server_number)
 330
 331     def copy_share_to_server(self, uri, share_number, server_number):
 332         ss = self.g.servers_by_number[server_number]
 333         # Copy share i from the directory associated with the first
 334         # storage server to the directory associated with this one.
 335         assert self.g, "I tried to find a grid at self.g, but failed"
 336         assert self.shares, "I tried to find shares at self.shares, but failed"
 337         old_share_location = self.shares[share_number][2]
 338         new_share_location = os.path.join(ss.storedir, "shares")
 339         si = tahoe_uri.from_string(self.uri).get_storage_index()
 340         new_share_location = os.path.join(new_share_location,
 341                                           storage_index_to_dir(si))
 342         if not os.path.exists(new_share_location):
 343             os.makedirs(new_share_location)
 344         new_share_location = os.path.join(new_share_location,
 345                                           str(share_number))
 346         if old_share_location != new_share_location:
 347             shutil.copy(old_share_location, new_share_location)
 348         shares = self.find_uri_shares(uri)
 349         # Make sure that the storage server has the share.
 350         self.failUnless((share_number, ss.my_nodeid, new_share_location)
 351                         in shares)
 352
 353     def _pretty_shares_chart(self, uri):
 354         # Servers are labeled A-Z, shares are labeled 0-9
 355         letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 356         assert len(self.g.servers_by_number) < len(letters), \
 357             "This little printing function is only meant for < 26 servers"
 358         shares_chart = {}
 359         names = dict(zip([ss.my_nodeid
 360                           for _,ss in self.g.servers_by_number.iteritems()],
 361                          letters))
 362         for shnum, serverid, _ in self.find_uri_shares(uri):
 363             shares_chart.setdefault(shnum, []).append(names[serverid])
 364         return shares_chart
 365
 366     def test_good_share_hosts(self):
 367         self.basedir = "checker/BalancingAct/1115"
 368         self.set_up_grid(num_servers=1)
 369         c0 = self.g.clients[0]
 370         c0.DEFAULT_ENCODING_PARAMETERS['happy'] = 1
 371         c0.DEFAULT_ENCODING_PARAMETERS['n'] = 4
 372         c0.DEFAULT_ENCODING_PARAMETERS['k'] = 3
 373
 374         DATA = "data" * 100
 375         d = c0.upload(Data(DATA, convergence=""))
 376         def _stash_immutable(ur):
 377             self.imm = c0.create_node_from_uri(ur.get_uri())
 378             self.uri = self.imm.get_uri()
 379         d.addCallback(_stash_immutable)
 380         d.addCallback(lambda ign:
 381             self.find_uri_shares(self.uri))
 382         def _store_shares(shares):
 383             self.shares = shares
 384         d.addCallback(_store_shares)
 385
 386         def add_three(_, i):
 387             # Add a new server with just share 3
 388             self.add_server_with_share(i, self.uri, 3)
 389             #print self._pretty_shares_chart(self.uri)
 390         for i in range(1,5):
 391             d.addCallback(add_three, i)
 392
 393         def _check_and_repair(_):
 394             return self.imm.check_and_repair(Monitor())
 395         def _check_counts(crr, shares_good, good_share_hosts):
 396             prr = crr.get_post_repair_results()
 397             #print self._pretty_shares_chart(self.uri)
 398             self.failUnlessEqual(prr.get_share_counter_good(), shares_good)
 399             self.failUnlessEqual(prr.get_host_counter_good_shares(),
 400                                  good_share_hosts)
 401
 402         """
 403         Initial sharemap:
 404             0:[A] 1:[A] 2:[A] 3:[A,B,C,D,E]
 405           4 good shares, but 5 good hosts
 406         After deleting all instances of share #3 and repairing:
 407             0:[A,B], 1:[A,C], 2:[A,D], 3:[E]
 408           Still 4 good shares and 5 good hosts
 409             """
 410         d.addCallback(_check_and_repair)
 411         d.addCallback(_check_counts, 4, 5)
 412         d.addCallback(lambda _: self.delete_shares_numbered(self.uri, [3]))
 413         d.addCallback(_check_and_repair)
 414         d.addCallback(_check_counts, 4, 5)
 415         d.addCallback(lambda _: [self.g.break_server(sid)
 416                                  for sid in self.g.get_all_serverids()])
 417         d.addCallback(_check_and_repair)
 418         d.addCallback(_check_counts, 0, 0)
 419         return d
 420
 421 class AddLease(GridTestMixin, unittest.TestCase):
 422     # test for #875, in which failures in the add-lease call cause
 423     # false-negatives in the checker
 424
 425     def test_875(self):
 426         self.basedir = "checker/AddLease/875"
 427         self.set_up_grid(num_servers=1)
 428         c0 = self.g.clients[0]
 429         c0.DEFAULT_ENCODING_PARAMETERS['happy'] = 1
 430         self.uris = {}
 431         DATA = "data" * 100
 432         d = c0.upload(Data(DATA, convergence=""))
 433         def _stash_immutable(ur):
 434             self.imm = c0.create_node_from_uri(ur.get_uri())
 435         d.addCallback(_stash_immutable)
 436         d.addCallback(lambda ign:
 437             c0.create_mutable_file(MutableData("contents")))
 438         def _stash_mutable(node):
 439             self.mut = node
 440         d.addCallback(_stash_mutable)
 441
 442         def _check_cr(cr, which):
 443             self.failUnless(cr.is_healthy(), which)
 444
 445         # these two should work normally
 446         d.addCallback(lambda ign: self.imm.check(Monitor(), add_lease=True))
 447         d.addCallback(_check_cr, "immutable-normal")
 448         d.addCallback(lambda ign: self.mut.check(Monitor(), add_lease=True))
 449         d.addCallback(_check_cr, "mutable-normal")
 450
 451         really_did_break = []
 452         # now break the server's remote_add_lease call
 453         def _break_add_lease(ign):
 454             def broken_add_lease(*args, **kwargs):
 455                 really_did_break.append(1)
 456                 raise KeyError("intentional failure, should be ignored")
 457             assert self.g.servers_by_number[0].remote_add_lease
 458             self.g.servers_by_number[0].remote_add_lease = broken_add_lease
 459         d.addCallback(_break_add_lease)
 460
 461         # and confirm that the files still look healthy
 462         d.addCallback(lambda ign: self.mut.check(Monitor(), add_lease=True))
 463         d.addCallback(_check_cr, "mutable-broken")
 464         d.addCallback(lambda ign: self.imm.check(Monitor(), add_lease=True))
 465         d.addCallback(_check_cr, "immutable-broken")
 466
 467         d.addCallback(lambda ign: self.failUnless(really_did_break))
 468         return d
 469
 470 class CounterHolder(object):
 471     def __init__(self):
 472         self._num_active_block_fetches = 0
 473         self._max_active_block_fetches = 0
 474
 475 from allmydata.immutable.checker import ValidatedReadBucketProxy
 476 class MockVRBP(ValidatedReadBucketProxy):
 477     def __init__(self, sharenum, bucket, share_hash_tree, num_blocks, block_size, share_size, counterholder):
 478         ValidatedReadBucketProxy.__init__(self, sharenum, bucket,
 479                                           share_hash_tree, num_blocks,
 480                                           block_size, share_size)
 481         self.counterholder = counterholder
 482
 483     def get_block(self, blocknum):
 484         self.counterholder._num_active_block_fetches += 1
 485         if self.counterholder._num_active_block_fetches > self.counterholder._max_active_block_fetches:
 486             self.counterholder._max_active_block_fetches = self.counterholder._num_active_block_fetches
 487         d = ValidatedReadBucketProxy.get_block(self, blocknum)
 488         def _mark_no_longer_active(res):
 489             self.counterholder._num_active_block_fetches -= 1
 490             return res
 491         d.addBoth(_mark_no_longer_active)
 492         return d
 493
 494 class TooParallel(GridTestMixin, unittest.TestCase):
 495     # bug #1395: immutable verifier was aggressively parallized, checking all
 496     # blocks of all shares at the same time, blowing our memory budget and
 497     # crashing with MemoryErrors on >1GB files.
 498
 499     def test_immutable(self):
 500         import allmydata.immutable.checker
 501         origVRBP = allmydata.immutable.checker.ValidatedReadBucketProxy
 502
 503         self.basedir = "checker/TooParallel/immutable"
 504
 505         # If any code asks to instantiate a ValidatedReadBucketProxy,
 506         # we give them a MockVRBP which is configured to use our
 507         # CounterHolder.
 508         counterholder = CounterHolder()
 509         def make_mock_VRBP(*args, **kwargs):
 510             return MockVRBP(counterholder=counterholder, *args, **kwargs)
 511         allmydata.immutable.checker.ValidatedReadBucketProxy = make_mock_VRBP
 512
 513         d = defer.succeed(None)
 514         def _start(ign):
 515             self.set_up_grid(num_servers=4)
 516             self.c0 = self.g.clients[0]
 517             self.c0.DEFAULT_ENCODING_PARAMETERS = { "k": 1,
 518                                                "happy": 4,
 519                                                "n": 4,
 520                                                "max_segment_size": 5,
 521                                                }
 522             self.uris = {}
 523             DATA = "data" * 100 # 400/5 = 80 blocks
 524             return self.c0.upload(Data(DATA, convergence=""))
 525         d.addCallback(_start)
 526         def _do_check(ur):
 527             n = self.c0.create_node_from_uri(ur.get_uri())
 528             return n.check(Monitor(), verify=True)
 529         d.addCallback(_do_check)
 530         def _check(cr):
 531             # the verifier works on all 4 shares in parallel, but only
 532             # fetches one block from each share at a time, so we expect to
 533             # see 4 parallel fetches
 534             self.failUnlessEqual(counterholder._max_active_block_fetches, 4)
 535         d.addCallback(_check)
 536         def _clean_up(res):
 537             allmydata.immutable.checker.ValidatedReadBucketProxy = origVRBP
 538             return res
 539         d.addBoth(_clean_up)
 540         return d
 541
 542     test_immutable.timeout = 80