From: Daira Hopwood Date: Tue, 28 May 2013 21:30:08 +0000 (+0100) Subject: Cloud backend: change the ChunkCache's replacement policy to LRU. fixes #1885 X-Git-Url: https://git.rkrishnan.org/components/%3C?a=commitdiff_plain;h=9e98686419da63bf7e284941483fe641d4b2f573;p=tahoe-lafs%2Ftahoe-lafs.git Cloud backend: change the ChunkCache's replacement policy to LRU. fixes #1885 Signed-off-by: Daira Hopwood --- diff --git a/src/allmydata/storage/backends/cloud/cloud_common.py b/src/allmydata/storage/backends/cloud/cloud_common.py index fda61e66..90fec844 100644 --- a/src/allmydata/storage/backends/cloud/cloud_common.py +++ b/src/allmydata/storage/backends/cloud/cloud_common.py @@ -38,7 +38,8 @@ def get_chunk_key(share_key, chunknum): DEFAULT_PREFERRED_CHUNK_SIZE = 512*1024 PREFERRED_CHUNK_SIZE = DEFAULT_PREFERRED_CHUNK_SIZE -PIPELINE_DEPTH = 4 +PIPELINE_DEPTH = 5 +CACHED_CHUNKS = 5 ZERO_CHUNKDATA = "\x00"*PREFERRED_CHUNK_SIZE @@ -574,38 +575,34 @@ class BackpressurePipeline(object): class ChunkCache(object): """I cache chunks for a specific share object.""" - def __init__(self, container, key, chunksize, nchunks=1, initial_cachemap={}): + def __init__(self, container, key, chunksize, cached_chunks=CACHED_CHUNKS, initial_cachemap={}): self._container = container self._key = key self._chunksize = chunksize - self._nchunks = nchunks + self._cached_chunks = cached_chunks # chunknum -> deferred data self._cachemap = initial_cachemap + self._lru = deque(sorted(initial_cachemap.keys())) self._pipeline = BackpressurePipeline(PIPELINE_DEPTH) - def set_nchunks(self, nchunks): - self._nchunks = nchunks - def _load_chunk(self, chunknum, chunkdata_d): d = self._container.get_object(get_chunk_key(self._key, chunknum)) eventual_chain(source=d, target=chunkdata_d) return d + def _discard(self): + while len(self._lru) > self._cached_chunks: + self.flush_chunk(self._lru.popleft()) + def get(self, chunknum, result_d): if chunknum in self._cachemap: # cache hit; never stall + self._lru.remove(chunknum) # takes O(cached_chunks) time, but that's fine + self._lru.append(chunknum) eventual_chain(source=self._cachemap[chunknum], target=result_d) return defer.succeed(None) - # Evict any chunks other than the first and last two, until there are - # three or fewer chunks left cached. - for candidate_chunknum in self._cachemap.keys(): - if len(self._cachemap) <= 3: - break - if candidate_chunknum not in (0, self._nchunks-2, self._nchunks-1): - self.flush_chunk(candidate_chunknum) - # cache miss; stall when the pipeline is full chunkdata_d = defer.Deferred() d = self._pipeline.add(1, self._load_chunk, chunknum, chunkdata_d) @@ -614,6 +611,8 @@ class ChunkCache(object): return res chunkdata_d.addCallback(_check) self._cachemap[chunknum] = chunkdata_d + self._lru.append(chunknum) + self._discard() eventual_chain(source=chunkdata_d, target=result_d) return d diff --git a/src/allmydata/storage/backends/cloud/immutable.py b/src/allmydata/storage/backends/cloud/immutable.py index 41f0dbb3..8091da28 100644 --- a/src/allmydata/storage/backends/cloud/immutable.py +++ b/src/allmydata/storage/backends/cloud/immutable.py @@ -9,7 +9,6 @@ from zope.interface import implements from allmydata.interfaces import IShareForReading, IShareForWriting from allmydata.util.assertutil import precondition, _assert -from allmydata.util.mathutil import div_ceil from allmydata.storage.common import CorruptStoredShareError, UnknownImmutableContainerVersionError, \ DataTooLargeError from allmydata.storage.backends.cloud import cloud_common @@ -162,9 +161,8 @@ class ImmutableCloudShareForReading(CloudShareBase, ImmutableCloudShareMixin, Cl self._total_size = total_size self._chunksize = chunksize - nchunks = div_ceil(total_size, chunksize) initial_cachemap = {0: defer.succeed(first_chunkdata)} - self._cache = ChunkCache(container, self._key, chunksize, nchunks, initial_cachemap) + self._cache = ChunkCache(container, self._key, chunksize, initial_cachemap=initial_cachemap) #print "ImmutableCloudShareForReading", total_size, chunksize, self._key header = first_chunkdata[:self.HEADER_SIZE] diff --git a/src/allmydata/storage/backends/cloud/mutable.py b/src/allmydata/storage/backends/cloud/mutable.py index 2314f52f..7c9a2ead 100644 --- a/src/allmydata/storage/backends/cloud/mutable.py +++ b/src/allmydata/storage/backends/cloud/mutable.py @@ -123,7 +123,6 @@ class MutableCloudShare(CloudShareBase, CloudShareReaderMixin): def _set_total_size(self, total_size): self._total_size = total_size self._nchunks = div_ceil(self._total_size, self._chunksize) - self._cache.set_nchunks(self._nchunks) def log(self, *args, **kwargs): if self.parent: