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

C[omp]ute

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

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; 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); The Bolivian Case Against Chile At The Hague; Clear, Cogent Economic Arguments For Immigration; A Program To Say If I Am Working; Decent Cards For Ill People; New Photo; Luksic And Barrick Gold; President Bachelet's Speech; Baltimore Primer; libxml2 Parsing Stream; configure.ac Recipe For Library Path; The Davalos Affair For Idiots; Not The Onion: Google Fireside Chat w Kissinger; Bicycle Wheels, Inertia, and Energy; Another Tax Fraud; Google's Borg; A Verion That Redirects To Local HTTP Server; Spanish Accents For Idiots; Aluminium Cans; Advice on Spray Painting; Female View of Online Chat From a Male; UX Reading List; S4 Subgroups - Geometric Interpretation; Fucking Email; The SQM Affair For Idiots; Using Kolmogorov Complexity; Oblique Strategies in bash; Curses Tools; Markov Chain Monte Carlo Without all the Bullshit; Email Para Matias Godoy Mercado; The Penta Affair For Idiots; Example Code To Create numpy Array in C; Good Article on Bias in Graphic Design (NYTimes); Do You Backup github?; Data Mining Books; SimpleDateFormat should be synchronized; British Words; Chinese Govt Intercepts External Web To DDOS github; Numbering Permutations; Teenage Engineering - Low Price Synths; GCHQ Can Do Whatever It Wants; Dublinesque; A Cryptographic SAT Solver; Security Challenges; Word Lists for Crosswords; 3D Printing and Speaker Design; Searchable Snowden Archive; XCode Backdoored; Derived Apps Have Malware (CIA); Rowhammer - Hacking Software Via Hardware (DRAM) Bugs; Immutable SQL Database (Kinda); Tor GPS Tracker; That PyCon Dongle Mess...; ASCII Fluid Dynamics; Brandalism; Table of Shifter, Cassette and Derailleur Compatability; Lenovo Demonstrates How Bad HTTPS Is; Telegraph Owned by HSBC; Smaptop - Sunrise (Music)

© 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,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# 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.

    Parameters:
      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')
    else:
        total = int(total)
    return total


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

    Parameters:
      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
        counter.put()

    db.run_in_transaction(txn)
    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.

    Parameters:
      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
            config.put()

    db.run_in_transaction(txn)

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!

Thanks!

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,
Andrew

Comment on this post