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This is Ian Ozsvald's blog (@IanOzsvald), I'm an entrepreneurial geek, a Data Science/ML/NLP/AI consultant, author of O'Reilly's High Performance Python book, co-organiser of PyDataLondon, a Pythonista, co-founder of ShowMeDo and also a Londoner. Here's a little more about me.

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19 February 2015 - 11:35Starting Spark 1.2 and PySpark (and ElasticSearch and PyPy)

The latest PySpark (1.2) is feeling genuinely useful, late last year I had a crack at running Apache Spark 1.0 and PySpark and it felt a bit underwhelming (too much fanfare, too many bugs). The media around Spark continues to grow and e.g. today’s hackernews thread on the new DataFrame API has a lot of positive discussion and the lazily evaluated pandas-like dataframes built from a wide variety of data sources feels very powerful. Continuum have also just announced PySpark+GlusterFS.

One surprising fact is that Spark is Python 2.7 only at present, feature request 4897 is for Python 3 support (go vote!) which requires some cloud pickling to be fixed. Using the end-of-line Python release feels a bit daft. I’m using Linux Mint 17.1 which is based on Ubuntu 14.04 64bit. I’m using the pre-built spark-1.2.0-bin-hadoop2.4.tgz via their downloads page and ‘it just works’. Using my global Python 2.7.6 and additional IPython install (via apt-get):

spark-1.2.0-bin-hadoop2.4 $ IPYTHON=1 bin/pyspark
...
IPython 1.2.1 -- An enhanced Interactive Python.
...
 Welcome to
 ____              __
 / __/__  ___ _____/ /__
 _\ \/ _ \/ _ `/ __/  '_/
 /__ / .__/\_,_/_/ /_/\_\   version 1.2.0
 /_/
Using Python version 2.7.6 (default, Mar 22 2014 22:59:56)
 SparkContext available as sc.
 >>>

Note the IPYTHON=1, without that you get a vanilla shell, with it it’ll use IPython if it is in the search path. IPython lets you interactively explore the “sc” Spark context using tab completion which really helps at the start. To run one of the included demos (e.g. wordcount) you can use the spark-submit script:

spark-1.2.0-bin-hadoop2.4/examples/src/main/python 
$ ../../../../bin/spark-submit wordcount.py kmeans.py  # count words in kmeans.py

For my use case we were initially after sparse matrix support, sadly they’re only available for Scala/Java at present. By stepping back from my sklean/scipy sparse solution for a minute and thinking a little more map/reduce I could just as easily split the problem into number of counts and that parallelises very well in Spark (though I’d love to see sparse matrices in PySpark!).

I’m doing this with my contract-recruitment client via my ModelInsight as we automate recruitment, there’s a press release out today outlining a bit of what we do. One of the goals is to move to a more unified research+deployment approach, rather than lots of tooling in R&D which we then streamline for production, instead we hope to share similar tooling between R&D and production so deployment and different scales of data are ‘easier’.

I tried the latest PyPy 2.5 (running Python 2.7) and it ran PySpark just fine. Using PyPy 2.5 a  prime-search example takes 6s vs 39s with vanilla Python 2.7, so in-memory processing using RDDs rather than numpy objects might be quick and convenient (has anyone trialled this?). To run using PyPy set PYSPARK_PYTHON:

$ PYSPARK_PYTHON=~/pypy-2.5.0-linux64/bin/pypy ./pyspark

I’m used to working with Anaconda environments and for Spark I’ve setup a Python 2.7.8 environment (“conda create -n spark27 anaconda python=2.7”) & IPython 2.2.0. Whichever Python is in the search path or is specified at the command line is used by the pyspark script.

The next challenge to solve was integration with ElasticSearch for storing outputs. The official docs are a little tough to read as a non-Java/non-Hadoop programmer and they don’t mention PySpark integration, thankfully there’s a lovely 4-part blog sequence which “just works”:

  1. ElasticSearch and Python (no Spark but it sets the groundwork)
  2. Reading & Writing ElasticSearch using PySpark
  3. Sparse Matrix Multiplication using PySpark
  4. Dense Matrix Multiplication using PySpark

To summarise the above with a trivial example, to output to ElasticSearch using a trivial local dictionary and no other data dependencies:

$ wget http://central.maven.org/maven2/org/elasticsearch/
 elasticsearch-hadoop/2.1.0.Beta2/elasticsearch-hadoop-2.1.0.Beta2.jar
$ ~/spark-1.2.0-bin-hadoop2.4/bin/pyspark --jars 
 elasticsearch-hadoop-2.1.0.Beta2.jar
>>> res=sc.parallelize([1,2,3,4])
 >>> res2=res.map(lambda x: ('key', {'name': str(x), 'sim':0.22}))
 >>> res2.collect()
 [('key', {'name': '1', 'sim': 0.22}),
 ('key', {'name': '2', 'sim': 0.22}),
 ('key', {'name': '3', 'sim': 0.22}),
 ('key', {'name': '4', 'sim': 0.22})]

>>>res2.saveAsNewAPIHadoopFile(path='-', 
 outputFormatClass="org.elasticsearch.hadoop.mr.EsOutputFormat", 
 keyClass="org.apache.hadoop.io.NullWritable", 
 valueClass="org.elasticsearch.hadoop.mr.LinkedMapWritable", 
 conf={"es.resource": "myindex/mytype"})

The above creates a list of 4 dictionaries and then sends them to a local ES store using “myindex” and “mytype” for each new document.  Before I found the above I used this older solution which also worked just fine.

Running the local interactive session using a mock cluster was pretty easy. The docs for spark-standalone are a good start:

sbin $ ./start-master.sh
 #  the log (full path is reported by the script so you could `tail -f `) shows
 # 15/02/17 14:11:46 INFO Master: 
 # Starting Spark master at spark://ian-Latitude-E6420:7077
 # which gives the link to the browser view of the master machine which is 
 # probably on :8080 (as shown here http://www.mccarroll.net/blog/pyspark/).
#Next start a single worker:
sbin $ ./start-slave.sh 0 spark://ian-Latitude-E6420:7077
 # and the logs will show a link to another web page for each worker 
 # (probably starting at :4040).
#Next you can start a pySpark IPython shell for local experimentation:
$ IPYTHON=1 ~/data/libraries/spark-1.2.0-bin-hadoop2.4/bin/pyspark 
  --master spark://ian-Latitude-E6420:7077
 # (and similarity you could run a spark-shell to do the same with Scala)
#Or we can run their demo code using the master node you've configured setup:
$ ~/spark-1.2.0-bin-hadoop2.4/bin/spark-submit 
  --master spark://ian-Latitude-E6420:7077 
  ~/spark-1.2.0-bin-hadoop2.4/examples/src/main/python/wordcount.py README.txt

Note if you tried to run the above spark-submit (which specifies the –master to connect to) and you didn’t have a master node, you’d see log messages like:

15/02/17 14:14:25 INFO AppClient$ClientActor: 
 Connecting to master spark://ian-Latitude-E6420:7077...
15/02/17 14:14:25 WARN AppClient$ClientActor: 
 Could not connect to akka.tcp://sparkMaster@ian-Latitude-E6420:7077: 
 akka.remote.InvalidAssociation: 
 Invalid address: akka.tcp://sparkMaster@ian-Latitude-E6420:7077
15/02/17 14:14:25 WARN Remoting: Tried to associate with 
 unreachable remote address 
 [akka.tcp://sparkMaster@ian-Latitude-E6420:7077]. 
 Address is now gated for 5000 ms, all messages to this address will 
 be delivered to dead letters. 
 Reason: Connection refused: ian-Latitude-E6420/127.0.1.1:7077

If you had a master node running but you hadn’t setup a worker node then after doing the spark-submit it’ll hang for 5+ seconds and then start to report:

15/02/17 14:16:16 WARN TaskSchedulerImpl: 
 Initial job has not accepted any resources; 
 check your cluster UI to ensure that workers are registered and 
 have sufficient memory

and if you google that without thinking about the worker node then you’d come to this diagnostic page  which leads down a small rabbit hole…

Stuff I’d like to know:

  • How do I read easily from MongoDB using an RDD (in Hadoop format) in PySpark (do you have a link to an example?)
  • Who else in London is using (Py)Spark? Maybe catch-up over a coffee?

Ian applies Data Science as an AI/Data Scientist for companies in ModelInsight, sign-up for Data Science tutorials in London. Historically Ian ran Mor Consulting. He also founded the image and text annotation API Annotate.io, co-authored SocialTies, programs Python, authored The Screencasting Handbook, lives in London and is a consumer of fine coffees.

18 Comments | Tags: ArtificialIntelligence, Data science, Life, pydata, Python