From: Brian Warner Date: Tue, 18 Nov 2008 07:29:44 +0000 (-0700) Subject: tahoe.cfg: add controls for k and N (and shares-of-happiness) X-Git-Tag: allmydata-tahoe-1.3.0~417 X-Git-Url: https://git.rkrishnan.org/components/%22news.html/configuration.txt?a=commitdiff_plain;h=cae54ab118553e4e41bafbdade902603a84d85f6;p=tahoe-lafs%2Ftahoe-lafs.git tahoe.cfg: add controls for k and N (and shares-of-happiness) --- diff --git a/NEWS b/NEWS index 3302133c..91717f05 100644 --- a/NEWS +++ b/NEWS @@ -61,6 +61,9 @@ commented out. (ticket #518) tahoe.cfg now has controls for the foolscap "keepalive" and "disconnect" timeouts (#521). +tahoe.cfg now has controls for the encoding parameters: "shares.needed" and +"shares.total" in the "[client]" section. The default parameters are still +3-of-10. ** CLI Changes diff --git a/docs/configuration.txt b/docs/configuration.txt index 2d92fef1..5cc658ca 100644 --- a/docs/configuration.txt +++ b/docs/configuration.txt @@ -232,6 +232,40 @@ stats_gatherer.furl = (FURL string, optional) If provided, the node will connect to the given stats gatherer and provide it with operational statistics. +shares.needed = (int, optional) aka "k" +shares.total = (int, optional) aka "N", N >= k +shares.happy = (int, optional) k <= happy <= N + + These three values set the default encoding parameters. Each time a new file + is uploaded, erasure-coding is used to break the ciphertext into separate + pieces. There will be "N" (i.e. shares.total) pieces created, and the file + will be recoverable if any "k" (i.e. shares.needed) pieces are retrieved. + The default values are 3-of-10 (i.e. shares.needed = 3, shares.total = 10). + Setting k to 1 is equivalent to simple replication (uploading N copies of + the file). + + These values control the tradeoff between storage overhead, performance, and + reliability. To a first approximation, a 1MB file will use (1MB*N/k) of + backend storage space (the actual value will be a bit more, because of other + forms of overhead). Up to N-k shares can be lost before the file becomes + unrecoverable, so assuming there are at least N servers, up to N-k servers + can be offline without losing the file. So large N/k ratios are more + reliable, and small N/k ratios use less disk space. Clearly, k must never be + smaller than N. + + Large values of N will slow down upload operations slightly, since more + servers must be involved, and will slightly increase storage overhead due to + the hash trees that are created. Large values of k will cause downloads to + be marginally slower, because more servers must be involved. N cannot be + larger than 256, because of the 8-bit erasure-coding algorithm that Tahoe + uses. + + If servers are lost during an upload, shares.happy determines whether the + upload is considered successful or not. If at least "shares.happy" shares + were placed, the upload is declared a success, otherwise it is declared a + failure. The default value is 7. This value must not be smaller than k nor + larger than N. + == Storage Server Configuration == diff --git a/src/allmydata/client.py b/src/allmydata/client.py index 5f048bfa..cde8037d 100644 --- a/src/allmydata/client.py +++ b/src/allmydata/client.py @@ -65,6 +65,7 @@ class Client(node.Node, pollmixin.PollMixin): node.Node.__init__(self, basedir) self.started_timestamp = time.time() self.logSource="Client" + self.DEFAULT_ENCODING_PARAMETERS = self.DEFAULT_ENCODING_PARAMETERS.copy() self.init_introducer_client() self.init_stats_provider() self.init_lease_secret() @@ -185,6 +186,10 @@ class Client(node.Node, pollmixin.PollMixin): def init_client(self): helper_furl = self.get_config("client", "helper.furl", None) + DEP = self.DEFAULT_ENCODING_PARAMETERS + DEP["k"] = int(self.get_config("client", "shares.needed", DEP["k"])) + DEP["n"] = int(self.get_config("client", "shares.total", DEP["n"])) + DEP["happy"] = int(self.get_config("client", "shares.happy", DEP["happy"])) convergence_s = self.get_or_create_private_config('convergence', _make_secret) self.convergence = base32.a2b(convergence_s) self._node_cache = weakref.WeakValueDictionary() # uri -> node diff --git a/src/allmydata/scripts/create_node.py b/src/allmydata/scripts/create_node.py index 95049cf4..e0a7bf09 100644 --- a/src/allmydata/scripts/create_node.py +++ b/src/allmydata/scripts/create_node.py @@ -104,6 +104,9 @@ def create_client(basedir, config, out=sys.stdout, err=sys.stderr): c.write("helper.furl =\n") c.write("#key_generator.furl =\n") c.write("#stats_gatherer.furl =\n") + c.write("#shares.needed = 3\n") + c.write("#shares.happy = 7\n") + c.write("#shares.total = 10\n") c.write("\n") boolstr = {True:"true", False:"false"} diff --git a/src/allmydata/test/common.py b/src/allmydata/test/common.py index 63ebf2dd..e95a59d1 100644 --- a/src/allmydata/test/common.py +++ b/src/allmydata/test/common.py @@ -418,6 +418,10 @@ class SystemTestMixin(pollmixin.PollMixin, testutil.StallMixin): if self.stats_gatherer_furl: write("stats_gatherer.furl", self.stats_gatherer_furl) + # give subclasses a chance to append liens to the node's tahoe.cfg + # files before they are launched. + self._set_up_nodes_extra_config() + # start client[0], wait for it's tub to be ready (at which point it # will have registered the helper furl). c = self.add_service(client.Client(basedir=basedirs[0])) @@ -452,6 +456,10 @@ class SystemTestMixin(pollmixin.PollMixin, testutil.StallMixin): d.addCallback(_connected) return d + def _set_up_nodes_extra_config(self): + # for overriding by subclasses + pass + def _grab_stats(self, res): d = self.stats_gatherer.poll() return d diff --git a/src/allmydata/test/test_upload.py b/src/allmydata/test/test_upload.py index 475051a8..6671b361 100644 --- a/src/allmydata/test/test_upload.py +++ b/src/allmydata/test/test_upload.py @@ -7,11 +7,12 @@ from twisted.python import log from twisted.internet import defer from foolscap import eventual -from allmydata import uri +from allmydata import uri, monitor from allmydata.immutable import upload from allmydata.interfaces import IFileURI, FileTooLargeError, NotEnoughSharesError from allmydata.util.assertutil import precondition from allmydata.util.deferredutil import DeferredListShouldSucceed +from common import SystemTestMixin from common_util import ShouldFailMixin MiB = 1024*1024 @@ -542,6 +543,31 @@ class StorageIndex(unittest.TestCase): d.addCallback(_done) return d +class EncodingParameters(SystemTestMixin, unittest.TestCase): + def test_configure_parameters(self): + self.basedir = self.mktemp() + DATA = "data" * 100 + u = upload.Data(DATA, convergence="") + d = self.set_up_nodes() + d.addCallback(lambda res: self.clients[0].upload(u)) + d.addCallback(lambda ur: self.clients[0].create_node_from_uri(ur.uri)) + m = monitor.Monitor() + d.addCallback(lambda fn: fn.check(m)) + def _check(cr): + data = cr.get_data() + self.failUnlessEqual(data["count-shares-needed"], 7) + self.failUnlessEqual(data["count-shares-expected"], 12) + d.addCallback(_check) + return d + + def _set_up_nodes_extra_config(self): + f = open(os.path.join(self.getdir("client0"), "tahoe.cfg"), "wt") + f.write("\n") + f.write("[client]\n") + f.write("shares.needed = 7\n") + f.write("shares.total = 12\n") + f.write("\n") + f.close() # TODO: # upload with exactly 75 peers (shares_of_happiness)