class SkewCostComponent(AbstractCostComponent):
def __init__(self, state):
AbstractCostComponent.__init__(self, state)
self.debug = LOG.isEnabledFor(logging.DEBUG)
# Keep track of how many times that we accessed each node
self.nodeCounts = Histogram()
self.workload_segments = [ ]
# Pre-split the workload into separate intervals
self.splitWorkload()
## DEF
def getCostImpl(self, design):
"""Calculate the network cost for each segment for skew analysis"""
# If there is only one node, then the cost is always zero
if self.state.num_nodes == 1:
LOG.info("Computed Skew Cost: %f", 0.0)
return 0.0
self.nodeCounts
op_counts = [ 0 ] * self.state.skew_segments
segment_skew = [ 0 ] * self.state.skew_segments
for i in range(0, len(self.workload_segments)):
# TODO: We should cache this so that we don't have to call it twice
segment_skew[i], op_counts[i] = self.calculateSkew(design, self.workload_segments[i])
weighted_skew = sum([segment_skew[i] * op_counts[i] for i in xrange(len(self.workload_segments))])
cost = weighted_skew / float(sum(op_counts))
LOG.info("Computed Skew Cost: %f", cost)
return cost
## DEF
def calculateSkew(self, design, segment):
"""
Calculate the cluster skew factor for the given workload segment
See Alg.#3 from Pavlo et al. 2012:
http://hstore.cs.brown.edu/papers/hstore-partitioning.pdf
"""
if self.debug:
LOG.debug("Computing skew cost for %d sessions over %d segments", \
len(segment), self.state.skew_segments)
self.nodeCounts.clear()
# Iterate over each session and get the list of nodes
# that we estimate that each of its operations will need to touch
num_ops = 0
err_ops = 0
for sess in segment:
for op in sess['operations']:
# Skip anything that doesn't have a design configuration
if not design.hasCollection(op['collection']):
if self.debug: LOG.debug("Not in design: SKIP - %s Op #%d on %s", op['type'], op['query_id'], op['collection'])
continue
if design.isRelaxed(op['collection']):
if self.debug: LOG.debug("Relaxed: SKIP - %s Op #%d on %s", op['type'], op['query_id'], op['collection'])
continue
col_info = self.state.collections[op['collection']]
cache = self.state.getCacheHandle(col_info)
# This just returns an estimate of which nodes we expect
# the op to touch. We don't know exactly which ones they will
# be because auto-sharding could put shards anywhere...
try:
node_ids = self.state.__getNodeIds__(cache, design, op)
map(self.nodeCounts.put, node_ids)
num_ops += 1
except:
if self.debug:
LOG.warn("Failed to estimate touched nodes for op\n%s" % pformat(op))
err_ops += 1
continue
## FOR (op)
## FOR (sess)
if self.debug: LOG.info("Total ops %s, errors %s", num_ops, err_ops)
if self.debug: LOG.debug("Node Count Histogram:\n%s", self.nodeCounts)
total = self.nodeCounts.getSampleCount()
if not total:
return (0.0, num_ops)
best = 1 / float(self.state.num_nodes)
skew = 0.0
for i in xrange(self.state.num_nodes):
ratio = self.nodeCounts.get(i, 0) / float(total)
if ratio < best:
ratio = best + ((1 - ratio/best) * (1 - best))
skew += math.log(ratio / best)
return skew / (math.log(1 / best) * self.state.num_nodes), num_ops
## DEF
## -----------------------------------------------------------------------
## WORKLOAD SEGMENTATION
## -----------------------------------------------------------------------
def splitWorkload(self):
"""Divide the workload up into segments for skew analysis"""
start_time = None
end_time = None
for i in xrange(len(self.state.workload)):
if start_time is None or start_time > self.state.workload[i]['start_time']:
start_time = self.state.workload[i]['start_time']
if end_time is None or end_time < self.state.workload[i]['end_time']:
end_time = self.state.workload[i]['end_time']
assert not start_time is None,\
"Failed to find start time in %d sessions" % len(self.state.workload)
assert not end_time is None,\
"Failed to find end time in %d sessions" % len(self.state.workload)
if self.debug:
LOG.debug("Workload Segments - START:%d / END:%d", start_time, end_time)
self.workload_segments = [ [] for i in xrange(0, self.state.skew_segments) ]
segment_h = Histogram()
for sess in self.state.workload:
idx = self.getSessionSegment(sess, start_time, end_time)
segment_h.put(idx)
assert idx >= 0 and idx < self.state.skew_segments,\
"Invalid workload segment '%d' for Session #%d\n%s" % (idx, sess['session_id'], segment_h)
self.workload_segments[idx].append(sess)
## FOR
## DEF
def getSessionSegment(self, sess, start_time, end_time):
"""Return the segment offset that the given Session should be assigned to"""
timestamp = sess['start_time']
if timestamp == end_time: timestamp -= 1
ratio = (timestamp - start_time) / float(end_time - start_time)
return min(self.state.skew_segments-1, int(self.state.skew_segments * ratio)) # HACK
## DEF
## CLASS
def sessionizeWorkload(self):
"""
Split the Sessions based on the gap between operation times
"""
LOG.info("Sessionizing sample workload")
s = Sessionizer(self.metadata_db, randomize=self.random_sessionizer)
# We first feed in all of the operations in for each session
nextSessId = -1
origTotal = 0
origHistogram = Histogram()
sessions = [ ]
for sess in self.metadata_db.Session.fetch():
s.process(sess['session_id'], sess['operations'])
nextSessId = max(nextSessId, sess['session_id'])
origHistogram.put(len(sess['operations']))
origTotal += len(sess['operations'])
sessions.append(sess)
## FOR
nextSessId += 1
avg_ops = 0 if origHistogram.getSampleCount() == 0 else (origTotal / float(origHistogram.getSampleCount()))
LOG.info("BEFORE Sessionization\n" +
" # of Sessions: %d\n" +
" Avg Ops per Session: %.2f\n" +
" Next Session Id: %d", \
origHistogram.getSampleCount(), \
avg_ops, nextSessId)
# Then split them into separate sessions
s.calculateSessions()
newTotal = 0
newHistogram = Histogram()
# We have to do this because otherwise we will start to process
# the new sessions that we just inserted... I know...
for sess in sessions:
newSessions = s.sessionize(sess, nextSessId)
nextSessId += len(newSessions)
# And then add all of our new sessions
# Count the number of operations so that can see the change
if self.debug:
LOG.debug("Split Session %d [%d ops] into %d separate sessions", \
sess['session_id'], len(sess['operations']), len(newSessions))
totalOps = 0
for newSess in newSessions:
try:
newSess.save()
except:
LOG.error("Unexpected error when saving new Session\n%s", pformat(newSess))
raise
newOpCtr = len(newSess['operations'])
totalOps += newOpCtr
newHistogram.put(newOpCtr)
if self.debug:
LOG.debug("Session %d -> %d Ops" % (newSess['session_id'], newOpCtr))
# Make sure that all of our operations end up in a session
assert len(sess['operations']) == totalOps, \
"Expected %d operations, but new sessions only had %d" % (len(sess['operations']), totalOps)
newTotal += totalOps
# Mark the original session as deletable
# deletable.append(sess)
sess.delete()
## FOR
avg_ops = 0 if origHistogram.getSampleCount() == 0 else (origTotal / float(origHistogram.getSampleCount()))
LOG.info("AFTER Sessionization\n" +
" # of Sessions: %d\n" +
" Avg Ops per Session: %.2f", \
newHistogram.getSampleCount(), \
avg_ops)
if self.debug:
LOG.debug("Ops per Session\n%s" % newHistogram)
return
## DEF
## CLASS
def sessionizeWorkload(self):
"""
Split the Sessions based on the gap between operation times
"""
LOG.info("Sessionizing sample workload")
s = Sessionizer(self.metadata_db, randomize=self.random_sessionizer)
# We first feed in all of the operations in for each session
nextSessId = -1
origTotal = 0
origHistogram = Histogram()
sessions = []
for sess in self.metadata_db.Session.fetch():
s.process(sess['session_id'], sess['operations'])
nextSessId = max(nextSessId, sess['session_id'])
origHistogram.put(len(sess['operations']))
origTotal += len(sess['operations'])
sessions.append(sess)
## FOR
nextSessId += 1
avg_ops = 0 if origHistogram.getSampleCount() == 0 else (
origTotal / float(origHistogram.getSampleCount()))
LOG.info("BEFORE Sessionization\n" +
" # of Sessions: %d\n" +
" Avg Ops per Session: %.2f\n" +
" Next Session Id: %d", \
origHistogram.getSampleCount(), \
avg_ops, nextSessId)
# Then split them into separate sessions
s.calculateSessions()
newTotal = 0
newHistogram = Histogram()
# We have to do this because otherwise we will start to process
# the new sessions that we just inserted... I know...
for sess in sessions:
newSessions = s.sessionize(sess, nextSessId)
nextSessId += len(newSessions)
# And then add all of our new sessions
# Count the number of operations so that can see the change
if self.debug:
LOG.debug("Split Session %d [%d ops] into %d separate sessions", \
sess['session_id'], len(sess['operations']), len(newSessions))
totalOps = 0
for newSess in newSessions:
try:
newSess.save()
except:
LOG.error("Unexpected error when saving new Session\n%s",
pformat(newSess))
raise
newOpCtr = len(newSess['operations'])
totalOps += newOpCtr
newHistogram.put(newOpCtr)
if self.debug:
LOG.debug("Session %d -> %d Ops" %
(newSess['session_id'], newOpCtr))
# Make sure that all of our operations end up in a session
assert len(sess['operations']) == totalOps, \
"Expected %d operations, but new sessions only had %d" % (len(sess['operations']), totalOps)
newTotal += totalOps
# Mark the original session as deletable
# deletable.append(sess)
sess.delete()
## FOR
avg_ops = 0 if origHistogram.getSampleCount() == 0 else (
origTotal / float(origHistogram.getSampleCount()))
LOG.info("AFTER Sessionization\n" +
" # of Sessions: %d\n" +
" Avg Ops per Session: %.2f", \
newHistogram.getSampleCount(), \
avg_ops)
if self.debug:
LOG.debug("Ops per Session\n%s" % newHistogram)
return
## DEF
## CLASS
