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diskwatcher: cache growth results (which take 30s to generate) for 3 minutes, to help munin, which invokes it 6 times in a row every 5 minutes

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This commit is contained in:
Brian Warner 2009-01-25 17:06:39 -07:00
parent 9d6534d78b
commit 8d6bdb5856
1 changed files with 20 additions and 1 deletions
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21
misc/spacetime/diskwatcher.tac
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@ -25,7 +25,7 @@ results). Each line should be in the form:
# built-in graphs on web interface
import os.path, urllib
import os.path, urllib, time
from datetime import timedelta
from twisted.application import internet, service, strports
from twisted.web import server, resource, http, client
@ -72,6 +72,7 @@ class DiskWatcher(service.MultiService, resource.Resource):
def __init__(self):
assert os.path.exists("diskwatcher.tac") # run from the right directory
self.growth_cache = {}
service.MultiService.__init__(self)
resource.Resource.__init__(self)
self.store = Store("history.axiom")
@ -238,6 +239,23 @@ class DiskWatcher(service.MultiService, resource.Resource):
until the gatherer has been running and collecting data for that
long."""
# a note about workload: for our oldest storage servers, as of
# 25-Jan-2009, the first DB query here takes about 40ms per server
# URL (some take as little as 10ms). There are about 110 servers, and
# two queries each, so the growth() function takes about 7s to run
# for each timespan. We track 4 timespans, and find_total_*_space()
# takes about 2.3s to run, so calculate_growth_timeleft() takes about
# 27s. Each HTTP query thus takes 27s, and we have six munin plugins
# which perform HTTP queries every 5 minutes. By adding growth_cache(),
# I hope to reduce this: the first HTTP query will still take 27s,
# but the subsequent five should be about 2.3s each.
# we're allowed to cache this value for 3 minutes
if timespan in self.growth_cache:
(when, value) = self.growth_cache[timespan]
if time.time() - when < 3*60:
return value
td = timedelta(seconds=timespan)
now = extime.Time()
then = now - td
@ -278,6 +296,7 @@ class DiskWatcher(service.MultiService, resource.Resource):
if not num_nodes:
return None
self.growth_cache[timespan] = (time.time(), total_growth)
return total_growth
def getChild(self, path, req):