| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next


Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Iraq + The (UK) Governing Elite; Answering Some Hard Questions; Pinochet: The Dictator's Shadow; An Outsider's Guide To Julia Packages; Nobody gives a shit; Lepton Decay Irregularity; An Easier Way; Julia's BinDeps (aka How To Install Cairo); Good Example Of Good Police Work (And Anonymity Being Hard); Best Santiago Burgers; Also; Michael Emmerich (Vibrator Translator) Interview (Japanese Books); Clarice Lispector (Brazillian Writer); Books On Evolution; Looks like Ara (Modular Phone) is dead; Index - Translations From Chile; More Emotion in Chilean Wines; Week 7; Aeon Magazine (Science-ish); QM, Deutsch, Constructor Theory; Interesting Talk Transcripts; Interesting Suggestion Of Election Fraud; "Hard" Books; Articles or Papers on depolarizing the US; Textbook for "QM as complex probabilities"; SFO Get Libor Trader (14 years); Why Are There Still So Many Jobs?; Navier Stokes Incomplete; More on Benford; FBI Claimed Vandalism; Architectural Tessellation; Also: Go, Blake's 7; Delusions of Gender (book); Crypto AG DID work with NSA / GCHQ; UNUMS (Universal Number Format); MOOCs (Massive Open Online Courses); Interesting Looking Game; Euler's Theorem for Polynomials; Weeks 3-6; Reddit Comment; Differential Cryptanalysis For Dummies; Japanese Graphic Design; Books To Be Re-Read; And Today I Learned Bugs Need Clear Examples; Factoring a 67 bit prime in your head; Islamic Geometric Art; Useful Julia Backtraces from Tasks; Nothing, however, is lost with less discomfort than that which, when lost, cannot be missed; Article on Didion; Cost of Living by City; British Slavery; Derrida on Metaphor; African SciFi; Traits in Julia; Alternative Japanese Lit; Pulic Key as Address (Snow); Why Information Grows; The Blindness Of The Chilean Elite; Some Victoriagate Links; This Is Why I Left StackOverflow; New TLS Implementation; Maths for Physicists; How I Am 8; 1000 Word Philosophy; Cyberpunk Reading List; Detailed Discussion of Message Dispatch in ParserCombinator Library for Julia; FizzBuzz in Julia w Dependent Types; kokko - Design Shop in Osaka; Summary of Greece, Currently; LLVM and GPUs; See Also; Schoolgirl Groyps (Maths); Japanese Lit; Another Example - Modular Arithmetic; Music from United; Python 2 and 3 compatible alternative.; Read Agatha Christie for the Plot; A Constructive Look at TempleOS; Music Thread w Many Recommendations; Fixed Version; A Useful Julia Macro To Define Equality And Hash; k3b cdrom access, OpenSuse 13.1; Week 2; From outside, the UK looks less than stellar; Huge Fonts in VirtualBox; Keen - Complex Emergencies; The Fallen of World War II; Some Spanish Fiction; Calling C From Fortran 95; Bjork DJ Set; Z3 Example With Python; Week 1; Useful Guide To Starting With IJulia; UK Election + Media; Review: Reinventing Organizations; Inline Assembly With Julia / LLVM; Against the definition of types; Dumb Crypto Paper; The Search For Quasi-Periodicity...; Is There An Alternative To Processing?; CARDIAC (CARDboard Illustrative Aid to Computation)

© 2006-2015 Andrew Cooke (site) / post authors (content).

Improved Sharded Counter for Google AppEngine

From: andrew cooke <andrew@...>

Date: Thu, 4 Aug 2011 20:59:55 -0400

This is based on the code in the examples project, but has some fixes so that
it bootstraps properly after memcache is flushed and the like.

# Copyright 2008 Google Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#     http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
# Modified / extended / fixed by andrew@... to work across
# re-deploys, memcache flushes, etc.

from google.appengine.api import memcache 
from google.appengine.ext import db
import random

class GeneralCounterShardConfig(db.Model):
    """Tracks the number of shards for each named counter."""
    name = db.StringProperty(required=True)
    num_shards = db.IntegerProperty(required=True, default=20)

class GeneralCounterShard(db.Model):
    """Shards for each named counter"""
    name = db.StringProperty(required=True)
    count = db.IntegerProperty(required=True, default=0)

def get_count(name):
    """Retrieve the value for a given sharded counter.

      name - The name of the counter
    total = memcache.get('counter:' + name)
    if total is None:
        total = 0
        for counter in GeneralCounterShard.all().filter('name = ', name):
            total += counter.count
        memcache.add(name, str(total), 60, namespace='counter')
        total = int(total)
    return total

def increment(name):
    """Increment the value for a given sharded counter.

      name - The name of the counter
    config = GeneralCounterShardConfig.get_or_insert(name, name=name)

    def txn():
        index = random.randint(0, config.num_shards - 1)
        shard_name = name + str(index)
        counter = GeneralCounterShard.get_by_key_name(shard_name)
        if counter is None:
            counter = GeneralCounterShard(key_name=shard_name, name=name)
        counter.count += 1

    value = memcache.incr(name, namespace='counter')
    if value is None:
        value = get_count(name)
    return value

def increase_shards(name, num):
    """Increase the number of shards for a given sharded counter.
    Will never decrease the number of shards.

      name - The name of the counter
      num - How many shards to use

    config = GeneralCounterShardConfig.get_or_insert(name, name=name)

    def txn():
        if config.num_shards < num:
            config.num_shards = num


total = memcache.get('counter:' + name)

From: Steve Olechowski <sjo@...>

Date: Thu, 20 Sep 2012 14:16:29 -0500

from your improved sharded counter post, won't this line:

total = memcache.get('counter:' + name)

always be None because you are setting it everywhere else with   add(
name, namespace='counter') ?  I could be misunderstanding something...

i appreciate you sharing your work here as I have the same needs for a
more resiliant sharded counter!


Steve Olechowski

Re: total = memcache.get('counter:' + name)

From: andrew cooke <andrew@...>

Date: Fri, 21 Sep 2012 08:03:53 -0300

I no longer use this code (or Google App Engine), and I don't remember much
about it, but it certainly look slike you are right.

My best guess is that I modified the code to use namespace (after starting
with a manual prefix), and updated the post, but forgot to update that line.

Thanks for pointing it out,

Comment on this post