01 September 2017
4 comments
Web development,
Linux
I have this WebExtension addon. It's not very important. Just a web extension that does some hacks to GitHub pages when I open them in Firefox. The web extension is a folder with a manifest.json, icons/icon-48.png, tricks.js, README.md etc. To upload it to addons.mozilla.org I first have to turn the whole thing into a .zip file that I can upload.
So I discovered a neat way to make that zip file. It looks like this:
#!/bin/bash
DESTINATION=build-`cat manifest.json | jq -r .version`.zip
git archive --format=zip master > $DESTINATION
echo "Created..."
ls -lh $DESTINATION
You run it and it creates a build-1.0.zip file containing all the files that are checked into the git repo. So it discards my local "junk" such as backup files or other things that are mentioned in .gitignore (and .git/info/exclude).
I bet someone's going to laugh and say "Duhh! Of course!" but I didn't know you can do that easily. Hopefully posting this it'll help someone trying to do something similar.
Note; this depends on jq which is an amazing little program.
07 June 2017
0 comments
Go,
MacOSX,
Linux
"machma - Easy parallel execution of commands with live feedback"
This is so cool! https://github.com/fd0/machma
It's a command line program that makes it really easy to run any command line program in parallel. I.e. in separate processes with separate CPUs.
Something network bound
Suppose I have a file like this:
▶ wc -l urls.txt
30 urls.txt
▶ cat urls.txt | head -n 3
https://s3-us-west-2.amazonaws.com/org.mozilla.crash-stats.symbols-public/v1/wntdll.pdb/D74F79EB1F8D4A45ABCD2F476CCABACC2/wntdll.sym
https://s3-us-west-2.amazonaws.com/org.mozilla.crash-stats.symbols-public/v1/firefox.pdb/448794C699914DB8A8F9B9F88B98D7412/firefox.sym
https://s3-us-west-2.amazonaws.com/org.mozilla.crash-stats.symbols-public/v1/d2d1.pdb/CB8FADE9C48E44DA9A10B438A33114781/d2d1.sym
If I wanted to download all of these files with wget the traditional way would be:
▶ time cat urls.txt | xargs wget -q -P ./downloaded/
cat urls.txt 0.00s user 0.00s system 53% cpu 0.005 total
xargs wget -q -P ./downloaded/ 0.07s user 0.24s system 2% cpu 14.913 total
▶ ls downloaded | wc -l
30
▶ du -sh downloaded
21M downloaded
So it took 15 seconds to download 30 files that totals 21MB.
Now, let's do it with machama instead:
▶ time cat urls.txt | machma -- wget -q -P ./downloaded/ {}
cat urls.txt 0.00s user 0.00s system 55% cpu 0.004 total
machma -- wget -q -P ./downloaded/ {} 0.53s user 0.45s system 12% cpu 7.955 total
That uses 8 separate processors (because my laptop has 8 CPUs).
Because 30 / 8 ~= 4, it roughly does 4 iterations.
But note, it took 15 seconds to download 30 files synchronously. That's an average of 0.5s per file. The reason it doesn't take 4x0.5 seconds (instead of 8 seconds) is because it's at the mercy of bad luck and some of those 30 spiking a bit.
Something CPU bound
Now let's do something really CPU intensive; Guetzli compression.
▶ ls images | wc -l
7
▶ time find images -iname '*.jpg' | xargs -I {} guetzli --quality 85 {} compressed/{}
find images -iname '*.jpg' 0.00s user 0.00s system 40% cpu 0.009 total
xargs -I {} guetzli --quality 85 {} compressed/{} 35.74s user 0.68s system 99% cpu 36.560 total
And now the same but with machma:
▶ time find images -iname '*.jpg' | machma -- guetzli --quality 85 {} compressed/{}
processed 7 items (0 failures) in 0:10
find images -iname '*.jpg' 0.00s user 0.00s system 51% cpu 0.005 total
machma -- guetzli --quality 85 {} compressed/{} 58.47s user 0.91s system 546% cpu 10.857 total
Basically, it took only 11 seconds. This time there were fewer images (7) than there was CPUs (8), so basically the poor computer is doing super intensive CPU (and memory) work across all CPUs at the same time. The average time for each of these files is ~5 seconds so it's really interesting that even if you try to do this in parallel execution instead of taking a total of ~5 seconds, it took almost double that.
In conclusion
Such a handy tool to have around for command line stuff. I haven't looked at its code much but it's almost a shame that the project only has 300+ GitHub stars. Perhaps because it's kinda complete and doesn't need much more work.
Also, if you attempt all the examples above you'll notice that when you use the ... | xargs ... approach the stdout and stderr is a mess. For wget, that's why I used -q to silence it a bit. With machma you get a really pleasant color coded live output that tells you the state of the queue, possible failures and an ETA.
24 May 2017
0 comments
MacOSX,
Web development,
Linux
tl;dr; Guetzli, the new JPEG compression program from Google can save a bytes with little loss of quality.
Inspired by this blog post about Guetzli I thought I'd try it out with something that's relevant to my project, 300x300 JPGs that can be heavily compressed.
So I installed it (with Homebrew) on my MacBook Pro (late 2013) and picked 7 JPGs I had, and use in SongSearch. Which is interesting because these JPEGs have already been compressed once. They are taken from converting from much larger PNGs with PIL (Pillow) at quality rating 80%. In other words, this is Guetzli on top of PIL.
I ran one iteration for every image for the following qualities: 85%, 90%, 95%, 99%, 100%.
The results on the size are as follows:
| Image |
Average Size (bytes) |
% Smaller |
| original |
23497.0 |
0 |
| 85% |
16025.4 |
32% |
| 90% |
18829.4 |
20% |
| 95% |
21338.1 |
9.2% |
| 99% |
22705.3 |
3.4% |
| 100% |
22919.7 |
2.5% |
So, for example, if you choose the 90% quality you save, on average, 4,667B (4.6KB).
As you might already know, Guetzli is incredibly memory hungry and very very slow. On average each image compression took on average 4-6 seconds (higher quality, shorter times). Meaning, if you like Guetzli you probably need to build around it so that the compression happens in a build step or async somewhere and ideally you don't want to run too many compressions in parallel as it might cause CPU and memory overloading.
Now, how does it look?
Go to https://codepen.io/peterbe/pen/rmPMpm and stare at the screen to see if you can A) see which one is more compressed and B) if the one that is more compressed is too low quality.
What do you think?
Is it worth it?
Is the quality drop too much to save 10% on image sizes?
Please share your thoughts. Perhaps we can re-do this experiment with some slightly larger JPGs.
11 May 2017
0 comments
Django,
Web development,
Linux,
Python
I have an app that does a lot of Redis queries. It all runs in AWS with ElastiCache Redis. Due to the nature of the app, it stores really large hash tables in Redis. The application then depends on querying Redis for these. The question is; What is the best configuration possible for the fastest service possible?
Note! Last month I wrote Fastest cache backend possible for Django which looked at comparing Redis against Memcache. Might be an interesting read too if you're not sold on Redis.
Options
All options are variations on the compressor, serializer and parser which are things you can override in django-redis. All have an effect on the performance. Even compression, for if the number of bytes between Redis and the application is smaller, then it should have better network throughput.
Without further ado, here are the variations:
CACHES = {
"default": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/0',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
}
},
"json": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/1',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"SERIALIZER": "django_redis.serializers.json.JSONSerializer",
}
},
"ujson": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/2',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"SERIALIZER": "fastestcache.ujson_serializer.UJSONSerializer",
}
},
"msgpack": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/3',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"SERIALIZER": "django_redis.serializers.msgpack.MSGPackSerializer",
}
},
"hires": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/4',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"PARSER_CLASS": "redis.connection.HiredisParser",
}
},
"zlib": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/5',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"COMPRESSOR": "django_redis.compressors.zlib.ZlibCompressor",
}
},
"lzma": {
"BACKEND": "django_redis.cache.RedisCache",
"LOCATION": config('REDIS_LOCATION', 'redis://127.0.0.1:6379') + '/6',
"OPTIONS": {
"CLIENT_CLASS": "django_redis.client.DefaultClient",
"COMPRESSOR": "django_redis.compressors.lzma.LzmaCompressor"
}
},
}
As you can see, they each have a variation on the OPTIONS.PARSER_CLASS, OPTIONS.SERIALIZER or OPTIONS.COMPRESSOR.
The default configuration is to use redis-py and to pickle the Python objects to a bytestring. Pickling in Python is pretty fast but it has the disadvantage that it's Python specific so you can't have a Ruby application reading the same Redis database.
The Experiment
Note how I have one LOCATION per configuration. That's crucial for the sake of testing. That way one database is all JSON and another is all gzip etc.
What the benchmark does is that it measures how long it takes to READ a specific key (called benchmarking). Then, once it's done that it appends that time to the previous value (or [] if it was the first time). And lastly it writes that list back into the database. That way, towards the end you have 1 key whose value looks something like this: [0.013103008270263672, 0.003879070281982422, 0.009411096572875977, 0.0009970664978027344, 0.0002830028533935547, ..... MANY MORE ....].
Towards the end, each of these lists are pretty big. About 500 to 1,000 depending on the benchmark run.
In the experiment I used wrk to basically bombard the Django server on the URL /random (which makes a measurement with a random configuration). On the EC2 experiment node, it finalizes around 1,300 requests per second which is a decent number for an application that does a fair amount of writes.
The way I run the Django server is with uwsgi like this:
uwsgi --http :8000 --wsgi-file fastestcache/wsgi.py --master --processes 4 --threads 2
And the wrk command like this:
wrk -d30s "http://127.0.0.1:8000/random"
(that, by default, runs 2 threads on 10 connections)
At the end of starting the benchmarking, I open http://localhost:8000/summary which spits out a table and some simple charts.
An Important Quirk
One thing I noticed when I started was that the final numbers' average was very different from the medians. That would indicate that there are spikes. The graph on the right shows the times put into that huge Python list for the default configuration for the first 200 measurements. Note that there are little spikes but generally quite flat over time once it gets past the beginning.
Sure enough, it turns out that in almost all configurations, the time it takes to make the query in the beginning is almost order of magnitude slower than the times once the benchmark has started running for a while.
So in the test code you'll see that it chops off the first 10 times. Perhaps it should be more than 10. After all, if you don't like the spikes you can simply look at the median as the best source of conclusive truth.
The Code
The benchmarking code is here. Please be aware that this is quite rough. I'm sure there are many things that can be improved, but I'm not sure I'm going to keep this around.
The Equipment
The ElastiCache Redis I used was a cache.m3.xlarge (13 GiB, High network performance) with 0 shards and 1 node and no multi-zone enabled.
The EC2 node was a m4.xlarge Ubuntu 16.04 64-bit (4 vCPUs and 16 GiB RAM with High network performance).
Both the Redis and the EC2 were run in us-west-1c (North Virginia).
The Results
Here are the results! Sorry if it looks terrible on mobile devices.
root@ip-172-31-2-61:~# wrk -d30s "http://127.0.0.1:8000/random" && curl "http://127.0.0.1:8000/summary"
Running 30s test @ http://127.0.0.1:8000/random
2 threads and 10 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 9.19ms 6.32ms 60.14ms 80.12%
Req/Sec 583.94 205.60 1.34k 76.50%
34902 requests in 30.03s, 2.59MB read
Requests/sec: 1162.12
Transfer/sec: 88.23KB
TIMES AVERAGE MEDIAN STDDEV
json 2629 2.596ms 2.159ms 1.969ms
msgpack 3889 1.531ms 0.830ms 1.855ms
lzma 1799 2.001ms 1.261ms 2.067ms
default 3849 1.529ms 0.894ms 1.716ms
zlib 3211 1.622ms 0.898ms 1.881ms
ujson 3715 1.668ms 0.979ms 1.894ms
hires 3791 1.531ms 0.879ms 1.800ms
Best Averages (shorter better)
###############################################################################
██████████████████████████████████████████████████████████████ 2.596 json
█████████████████████████████████████ 1.531 msgpack
████████████████████████████████████████████████ 2.001 lzma
█████████████████████████████████████ 1.529 default
███████████████████████████████████████ 1.622 zlib
████████████████████████████████████████ 1.668 ujson
█████████████████████████████████████ 1.531 hires
Best Medians (shorter better)
###############################################################################
███████████████████████████████████████████████████████████████ 2.159 json
████████████████████████ 0.830 msgpack
████████████████████████████████████ 1.261 lzma
██████████████████████████ 0.894 default
██████████████████████████ 0.898 zlib
████████████████████████████ 0.979 ujson
█████████████████████████ 0.879 hires
Size of Data Saved (shorter better)
###############################################################################
█████████████████████████████████████████████████████████████████ 60K json
██████████████████████████████████████ 35K msgpack
████ 4K lzma
█████████████████████████████████████ 35K default
█████████ 9K zlib
████████████████████████████████████████████████████ 48K ujson
█████████████████████████████████████ 34K hires
Discussion Points
- There is very little difference once you avoid the
json serialized one.
msgpack is the fastest by a tiny margin. I prefer median over average because it's more important how it over a long period of time. - The
default (which is pickle) is fast too.
lzma and zlib compress the strings very well. Worth thinking about the fact that zlib is a very universal tool and makes the app "Python agnostic". - You probably don't want to use the
json serializer. It's fat and slow.
- Using
hires makes very little difference. That's a bummer.
- Considering how useful
zlib is (since you can fit so much much more data in your Redis) it's impressive that it's so fast too!
- I quite like
zlib. If you use that on the pickle serializer you're able to save ~3.5 times as much data.
- Laugh all you want but until today I had never heard of
lzma. So based on that odd personal fact, I'm pessmistic towards that as a compression choice.
Conclusion
This experiment has lead me to the conclusion that the best serializer is msgpack and the best compression is zlib. That is the best configuration for django-redis.
msgpack has implementation libraries for many other programming languages. Right now that doesn't matter for my application but if msgpack is both faster and more versatile (because it supports multiple languages) I conclude that to be the best serializer instead.
07 April 2017
5 comments
Web development,
Linux,
Python
tl;dr; Redis is twice as fast as memcached as a Django cache backend when installed using AWS ElastiCache. Only tested for reads.
Django has a wonderful caching framework. I think I say "wonderful" because it's so simple. Not because it has a hundred different bells or whistles. Each cache gets a name (e.g. "mymemcache" or "redis append only"). The only configuration you generally have to worry about is 1) what backed and 2) what location.
For example, to set up a memcached backend:
# this in settings.py
CACHES = {
'default': {
'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
'KEY_PREFIX': 'myapp',
'LOCATION': config('MEMCACHED_LOCATION', '127.0.0.1:11211'),
},
}
With that in play you can now do:
>>> from django.core.cache import caches
>>> caches['default'].set('key', 'value', 60) # 60 seconds
>>> caches['default'].get('key')
'value'
Django comes without built-in backend called django.core.cache.backends.locmem.LocMemCache which is basically a simply Python object in memory with no persistency between Python processes. This one is of course super fast because it involves no further network (local or remote) beyond the process itself. But it's not really useful because if you care about performance (which you probably are if you're here because of the blog post title) because it can't be reused amongst processes.
Anyway, the most common backends to use are:
These are semi-persistent and built for extremely fast key lookups. They can both be reached over TCP or via a socket.
What I wanted to see, is which one is fastest.
The Experiment
First of all, in this blog post I'm only measuring the read times of the various cache backends.
Here's the Django view function that is the experiment:
from django.conf import settings
from django.core.cache import caches
def run(request, cache_name):
if cache_name == 'random':
cache_name = random.choice(settings.CACHE_NAMES)
cache = caches[cache_name]
t0 = time.time()
data = cache.get('benchmarking', [])
t1 = time.time()
if random.random() < settings.WRITE_CHANCE:
data.append(t1 - t0)
cache.set('benchmarking', data, 60)
if data:
avg = 1000 * sum(data) / len(data)
else:
avg = 'notyet'
# print(cache_name, '#', len(data), 'avg:', avg, ' size:', len(str(data)))
return http.HttpResponse('{}\n'.format(avg))
It records the time to make a cache.get read and depending settings.WRITE_CHANCE it also does a write (but doesn't record that).
What it records is a list of floats. The content of that piece of data stored in the cache looks something like this:
[0.0007331371307373047] [0.0007331371307373047, 0.0002570152282714844] [0.0007331371307373047, 0.0002570152282714844, 0.0002200603485107422]
So the data grows from being really small to something really large. If you run this 1,000 times with settings.WRITE_CACHE of 1.0 the last time it has to fetch a list of 999 floats out of the cache backend.
You can either test it with 1 specific backend in mind and see how fast Django can do, say, 10,000 of these. Here's one such example:
$ wrk -t10 -c400 -d10s http://127.0.0.1:8000/default
Running 10s test @ http://127.0.0.1:8000/default
10 threads and 400 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 76.28ms 155.26ms 1.41s 92.70%
Req/Sec 349.92 193.36 1.51k 79.30%
34107 requests in 10.10s, 2.56MB read
Socket errors: connect 0, read 0, write 0, timeout 59
Requests/sec: 3378.26
Transfer/sec: 259.78KB
$ wrk -t10 -c400 -d10s http://127.0.0.1:8000/memcached
Running 10s test @ http://127.0.0.1:8000/memcached
10 threads and 400 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 96.87ms 183.16ms 1.81s 95.10%
Req/Sec 213.42 82.47 0.91k 76.08%
21315 requests in 10.09s, 1.57MB read
Socket errors: connect 0, read 0, write 0, timeout 32
Requests/sec: 2111.68
Transfer/sec: 159.27KB
$ wrk -t10 -c400 -d10s http://127.0.0.1:8000/redis
Running 10s test @ http://127.0.0.1:8000/redis
10 threads and 400 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 84.93ms 148.62ms 1.66s 92.20%
Req/Sec 262.96 138.72 1.10k 81.20%
25271 requests in 10.09s, 1.87MB read
Socket errors: connect 0, read 0, write 0, timeout 15
Requests/sec: 2503.55
Transfer/sec: 189.96KB
But an immediate disadvantage with this is that the "total final rate" (i.e. requests/sec) is likely to include so many other factors. However, you can see that LocMemcache got 3378.26 req/s, MemcachedCache got 2111.68 req/s and RedisCache got 2503.55 req/s.
The code for the experiment is available here: https://github.com/peterbe/django-fastest-cache
The Infra Setup
I created an AWS m3.xlarge EC2 Ubuntu node and two nodes in AWS ElastiCache. One 2-node memcached cluster based on cache.m3.xlarge and one 2-node 1-replica Redis cluster also based on cache.m3.xlarge.
The Django server was run with uWSGI like this:
uwsgi --http :8000 --wsgi-file fastestcache/wsgi.py --master --processes 6 --threads 10
The Results
Instead of hitting one backend repeatedly and reporting the "requests per second" I hit the "random" endpoint for 30 seconds and let it randomly select a cache backend each time and once that's done, I'll read each cache and look at the final massive list of timings it took to make all the reads. I run it like this:
wrk -t10 -c400 -d30s http://127.0.0.1:8000/random && curl http://127.0.0.1:8000/summary
...wrk output redacted...
TIMES AVERAGE MEDIAN STDDEV
memcached 5738 7.523ms 4.828ms 8.195ms
default 3362 0.305ms 0.187ms 1.204ms
redis 4958 3.502ms 1.707ms 5.591ms
Best Averages (shorter better)
###############################################################################
█████████████████████████████████████████████████████████████ 7.523 memcached
██ 0.305 default
████████████████████████████ 3.502 redis
Things to note:
- Redis is twice as fast as memcached.
- Pure Python
LocMemcache is 10 times faster than Redis.
- The table reports average and median. The ASCII bar chart shows only the averages.
- All three backends report huge standard deviations. The median is very different from the average.
- The average is probably the more interesting number since it more reflects the ups and downs of reality.
- If you compare the medians, Redis is 3 times faster than memcached.
- It's luck that Redis got fewer datapoints than memcached (4958 vs 5738) but it's as expected that the
LocMemcache backend only gets 3362 because the uWSGI server that is used is spread across multiple processes.
Other Things To Test
Perhaps pylibmc is faster than python-memcached.
TIMES AVERAGE MEDIAN STDDEV
pylibmc 2893 8.803ms 6.080ms 7.844ms
default 3456 0.315ms 0.181ms 1.656ms
redis 4754 3.697ms 1.786ms 5.784ms
Best Averages (shorter better)
###############################################################################
██████████████████████████████████████████████████████████████ 8.803 pylibmc
██ 0.315 default
██████████████████████████ 3.697 redis
Using pylibmc didn't make things much faster. What if we we pit memcached against pylibmc?:
TIMES AVERAGE MEDIAN STDDEV
pylibmc 3005 8.653ms 5.734ms 8.339ms
memcached 2868 8.465ms 5.367ms 9.065ms
Best Averages (shorter better)
###############################################################################
█████████████████████████████████████████████████████████████ 8.653 pylibmc
███████████████████████████████████████████████████████████ 8.465 memcached
What about that fancy hiredis Redis Python driver that's supposedly faster?
TIMES AVERAGE MEDIAN STDDEV
redis 4074 5.628ms 2.262ms 8.300ms
hiredis 4057 5.566ms 2.296ms 8.471ms
Best Averages (shorter better)
###############################################################################
███████████████████████████████████████████████████████████████ 5.628 redis
██████████████████████████████████████████████████████████████ 5.566 hiredis
These last two results are both surprising and suspicious. Perhaps the whole setup is wrong. Why wouldn't the C-based libraries be faster? Is it so incredibly dwarfed by the network I/O in the time between my EC2 node and the ElastiCache nodes?
In Conclusion
I personally like Redis. It's not as stable as memcached. On a personal server I've run for years the Redis server sometimes just dies due to corrupt memory and I've come to accept that. I don't think I've ever seen memcache do that.
But there are other benefits with Redis as a cache backend. With the django-redis library you have really easy access to the raw Redis connection and you can do much more advanced data structures. You can also cache certain things indefinitely. Redis also supports storing much larger strings than memcached (1MB for memcached and 512MB for Redis).
The conclusion is that Redis is faster than memcached by a factor of 2. Considering the other feature benefits you can get out of having a Redis server available, it's probably a good choice for your next Django project.
Bonus Feature
In big setups you most likely have a whole slur of web heads that are servers that do nothing by handle web requests. And these are configured to talk to databases and caches over the near network. However, so many of us have cheap servers on DigitalOcean or Linode where we run web servers, relational databases and cache servers all on the same machine. (I do. This blog is one of those where there is Nginx, Redis, memcached and PostgreSQL on a 4GB DigitalOcean NYC SSD machine).
So here's one last test where I installed a local Redis and a local memcached on the EC2 node itself:
$ cat .env | grep 127.0.0.1
MEMCACHED_LOCATION="127.0.0.1:11211"
REDIS_LOCATION="redis://127.0.0.1:6379/0"
Here are the results:
TIMES AVERAGE MEDIAN STDDEV
memcached 7366 3.456ms 1.380ms 5.678ms
default 3716 0.263ms 0.189ms 1.002ms
redis 5582 2.334ms 0.639ms 4.965ms
Best Averages (shorter better)
###############################################################################
█████████████████████████████████████████████████████████████ 3.456 memcached
████ 0.263 default
█████████████████████████████████████████ 2.334 redis
The conclusion of that last benchmark is that Redis is still faster and it's roughly 1.8x faster to run these backends on the web head than to use ElastiCache. Perhaps that just goes to show how amazingly fast the AWS inter-datacenter fiber network is!
06 January 2017
0 comments
Web development,
Linux,
Python
tl;dr; Here's a working .travis.yml file that works with ElasticSearch 5.1.1
I had to jump through hoops to get Travis-CI to run with ElasticSearch 5.1.1 and I thought I'd share. If you just do:
services:
- elasticsearch
This is from the Travis-CI documentation but this installs ElasticSearch 1.4. Not good enough. The instructions on the same page for using higher versions did not work for me.
To get a specific version you need to download it yourself and install it with dpkg -i but the problem is that if you want to use ElasticSearch version 5, you need to have Java 1.8. The short answer is that this is how you install Java 1.8:
addons:
apt:
packages:
- oracle-java8-set-default
But now you need to sudo so you need to add sudo: true in your .travis.yml. Bummer, because it makes the build a bit slower. However, a necessary evil.
The critical line I use to install it is this:
curl -O https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-5.1.1.deb && \
sudo dpkg -i --force-confnew elasticsearch-5.1.1.deb && \
sudo service elasticsearch start
I thought I could "upgrade" the existing install, but that breaks thinks. In other words you have to remove the services: - elasticsearch line or else it can't upgrade.
Now, during debugging I was not getting errors on the line:
sudo service elasticsearch start
So I add this to be sure the right version got installed:
#!/bin/bash
curl -v http://localhost:9200/
and then I can see that the right version was installed. It should look something like this:
* About to connect() to localhost port 9200 (#0)
* Trying 127.0.0.1... connected
> GET / HTTP/1.1
> User-Agent: curl/7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
> Host: localhost:9200
> Accept: */*
>
< HTTP/1.1 200 OK
< content-type: application/json; charset=UTF-8
< content-length: 327
<
{
"name" : "m_acpqT",
"cluster_name" : "elasticsearch",
"cluster_uuid" : "b4_KnK6KQmSx64C9o-81Ug",
"version" : {
"number" : "5.1.1",
"build_hash" : "5395e21",
"build_date" : "2016-12-06T12:36:15.409Z",
"build_snapshot" : false,
"lucene_version" : "6.3.0"
},
"tagline" : "You Know, for Search"
}
* Connection #0 to host localhost left intact
* Closing connection #0
Note the line that says "number" : "5.1.1",.
So, yay! Hopefully this will help someone else because it took me quite a while to get right.
13 May 2016
3 comments
Python,
Linux,
MacOSX
Did you see my blog post about Decorated Concurrency - Python multiprocessing made really really easy? If not, fear not. There, I'm demonstrating how I take a task of creating 100 thumbnails from a large JPG. First in serial, then concurrently, with a library called deco. The total time to get through the work massively reduces when you do it concurrently. No surprise. But what's interesting is that each individual task takes a lot longer. Instead of 0.29 seconds per image it took 0.65 seconds per image (...inside each dedicated processor).
The simple explanation, even from a layman like myself, must be that when doing so much more, concurrently, the whole operating system struggles to keep up with other little subtle tasks.
With deco you can either let Python's multiprocessing just use as many CPUs as your computer has (8 in the case of my Macbook Pro) or you can manually set it. E.g. @concurrent(processes=5) would spread the work across a max of 5 CPUs.
So, I ran my little experiment again for every number from 1 to 8 and plotted the results:
What to take away...
The blue bars is the time it takes, in total, from starting the program till the program ends. The lower the better.
The red bars is the time it takes, in total, to complete each individual task.
Meaning, when the number of CPUs is low you have to wait longer for all the work to finish and when the number of CPUs is high the computer needs more time to finish its work. This is an insight into over-use of operating system resources.
If the work is much much more demanding than this experiment (the JPG is only 3.3Mb and one thumbnail only takes 0.3 seconds to make) you might have a red bar on the far right that is too expensive for your server. Or worse, it might break things so that everything stops.
In conclusion...
Choose wisely. Be aware how "bound" the task is.
Also, remember that if the work of each individual task is too "light", the overhead of messing with multprocessing might actually cost more than it's worth.
The code
Here's the messy code I used:
import time
from PIL import Image
from deco import concurrent, synchronized
import sys
processes = int(sys.argv[1])
assert processes >= 1
assert processes <= 8
@concurrent(processes=processes)
def slow(times, offset):
t0 = time.time()
path = '9745e8.jpg'
img = Image.open(path)
size = (100 + offset * 20, 100 + offset * 20)
img.thumbnail(size, Image.ANTIALIAS)
img.save('thumbnails/{}.jpg'.format(offset), 'JPEG')
t1 = time.time()
times[offset] = t1 - t0
@synchronized
def run(times):
for index in range(100):
slow(times, index)
t0 = time.time()
times = {}
run(times)
t1 = time.time()
print "TOOK", t1-t0
print "WOULD HAVE TAKEN", sum(times.values())
UPDATE
I just wanted to verify that the experiment is valid that proves that CPU bound work hogs resources acorss CPUs that affects their individual performance.
Let's try to the similar but totally different workload of a Network bound task. This time, instead of resizing JPEGs, it waits for finishing HTTP GET requests.
So clearly it makes sense. The individual work withing each process is not generally slowed down much. A tiny bit, but not much. Also, I like the smoothness of the curve of the blue bars going from left to right. You can clearly see that it's reverse logarithmic.
20 April 2016
2 comments
Linux,
MacOSX
How did I not know about this until now?! .git/info/exlude is like .gitingore but yours to mess with. Thanks @willkg!
There are three ways to tell Git to ignore files.
.gitignore
A file you check in to the project. It's shared amongst developers on the project. It's just a plain text file where you write one line per file pattern that Git should not ask "Have you forgotten to check this in?"
Certain things that are good to put in there are...:
node_modules/
*.py[co]
.coverage
Ideally, this file should be as small as possible and every entry should confidently be something 100% of the developers on the team will want to ignore. If your particular editor has some convention for storing state or revision files, that does not belong on this file.
A reason to keep it short is that of purity and simplicity. Every edit of this file will require a git commit.
~/.gitignore_global
This is yours to keep and maintain. The file doesn't have to be in your home directory. (The ~/ is UNIX nomenclature for your OS user home directory). You can set it to be anything. Like:
$ git config --global core.excludesfile ~/projects/dotfiles/gitignore-global.txt
Here you put stuff you want to personally ignore in every Git project. New and old.
Good examples of things to put in it are...:
*~
.DS_Store
.env
settings/local.py
pip-log.txt
.git/info/exclude
This is a kinda mix between the two above mentioned ignore files. This is things only you want to ignore in a specific project. More or less "junk files" specific to a project. For example if you, in your Git clone, has some test scripts or a specific log file.
Suppose you have a little hack script or some specific config that is only applicable to the project at hand, this is where you add it. For example...:
run_webapp_uwsgi.sh
analyze_correlation_json_dumps.py
I hope this helps someone else who, like me, didn't know about .git/info/exclude until 2016.
26 January 2016
0 comments
Linux,
Web development
I have no problems admitting that I'm always finding SSL and certs and stuff like that confusing. And Let's Encrypt is no exception. However, with Let's Encrypt, apparently, all you need to do is download their software and run a command to get a couple of certificate files. No websites or forms to fill in. No need to create a .csr file. How hard can it be? After skimming some documentation and other blog posts I dug in. Turns out, it was quite doable.
To install it, I ran:
# pwd
/root
# git clone https://github.com/letsencrypt/letsencrypt
# cd letsencrypt
# pip install cryptography
# ./letsencrypt-auto
The reason I had to manually pip install cryptography was because the installer in ./letsencrypt-auto failed the first time.
Now it should be installed. To create the cert you have to temporarily stop Nginx. But I had to be quick because I don't want it to be down for long:
# /etc/init.d/nginx stop
# ./letsencrypt-auto certonly --standalone -d autocompeter.com
# /etc/init.d/nginx start
The first time I ran this I got Error: urn:acme:error:badNonce :: The client sent an unacceptable anti-replay nonce :: JWS has invalid anti-replay nonce which, according to this discussion is easy to bypass; simply try again. So I tried again, and the second time it worked.
This time it worked! Now I have 4 new files:
# ls -l /etc/letsencrypt/live/autocompeter.com/
total 0
lrwxrwxrwx 1 root root 32 Jan 25 08:04 cert.pem -> ../../archive/autocompeter.com/cert1.pem
lrwxrwxrwx 1 root root 33 Jan 25 08:04 chain.pem -> ../../archive/autocompeter.com/chain1.pem
lrwxrwxrwx 1 root root 37 Jan 25 08:04 fullchain.pem -> ../../archive/autocompeter.com/fullchain1.pem
lrwxrwxrwx 1 root root 35 Jan 25 08:04 privkey.pem -> ../../archive/autocompeter.com/privkey1.pem
Now add these lines to the Nginx config for that site:
listen 443;
ssl on;
ssl_certificate /etc/letsencrypt/live/autocompeter.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/autocompeter.com/privkey.pem;
ssl_session_timeout 5m;
ssl_session_cache shared:SSL:50m;
The new cert I just created expires in about 2 months. I created an entry in my calendar with an alert. I think I just need to run:
# /etc/init.d/nginx stop
# ./letsencrypt-auto certonly --standalone -d autocompeter.com
# /etc/init.d/nginx start
16 October 2015
2 comments
Linux,
MacOSX
It's one of those things; not hard to understand and certainly not an advanced trick but I sometimes see people miss out on this.
In bash there are sort of two ways of saying "Do this and then do that". You can either say "Do this and no matter what happens then do that" or you can say "Do this and if that worked also do that".
Examples
Suppose you have two command executables you want to run. They can succeed or fail.
$ echo "Do this and no matter what happens then do that"
$ ./command1 ; ./command2
If you run that, ./command2 will run even if ./command1 failed.
The other one is...
$ echo "Do this and if that worked also do that"
$ ./command1 && ./command2
You might recognize the && thing from JavaScript or Java or C or one of those. If you recognize it you might quickly also conclude that you can do this too:
$ echo "Do this and only if it failed do that"
$ ./command1 || ./command2
In this latter case only one of those (or none!) will succeed.
So when does this come in handy?
Here are some examples that I often use:
Meaning, I know my code is good to push, iff the tests pass
$ nosetests && git commit -a -m "some feature" && git push peterbe mybranch
Or if you might want to be alerted if something failed after the first command slowly takes its time to finish:
$ nosetests && say "Tests finished" || say "Work harder"
(say is an OSX specific command and not a built-in in bash)
The ; is useful when you don't care if the first command finished and this is more rare. For example:
$ rm static/ ; ./manage.py collectstatic --noinput
Why bother?
Perhaps it goes without saying, the reason for doing all of these is generally when the first command takes a long time and you don't want to sit and wait till it's finished to run the second time. By "piping them together" like this, the second command will safely start as soon as possible whilst you go away and pay attention to something else.
