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Apache Avro is becoming one of the most popular data serialization formats nowadays, andthis holds true particularly for Hadoop-based big data platforms because tools like Pig, Hive and of course Hadoop itselfnatively support reading and writing data in Avro format. Many users seem to enjoy Avro but I have heard manycomplaints about not being able to conveniently read or write Avro files with command line tools – “Avro is nice,but why do I have to write Java or Python code just to quickly see what’s in a binary Avro file, or discover at leastits Avro schema?”
To those users it comes as a surprise that Avro actually ships with exactly such command line tools but apparently theyare not prominently advertised or documented as such. In this short article I will show a few hands-on examples on how toread, write, compress and convert data from and to binary Avro using Avro Tools 1.7.4.
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- Example data
- Converting to and from binary Avro
Here is an overview of what we want to do:
Avro Keyboard Windows 7
- We will start with an example Avro schema and a corresponding data file in plain-text JSON format.
- We will use Avro Tools to convert the JSON file into binary Avro, without and with compression (Snappy), and from binaryAvro back to JSON.
You can get a copy of the latest stable Avro Tools jar file from theAvro Releases page. The actual file is in the
java
subdirectoryof a given Avro release version. Here is a direct link toavro-tools-1.7.4.jar(11 MB) on the US Apache mirror site.Save
avro-tools-1.7.4.jar
to a directory of your choice. I will use ~/avro-tools-1.7.4.jar
for theexamples shown below.Just run Avro Tools without any parameters to see what’s included:
Likewise run any particular tool without parameters to see its usage/help output. For example, here is the help of the
fromjson
tool:Note that most of the tools write to
STDOUT
, so normally you would like to pipe their output to a file via the Bash>
redirection operator (particularly when working with large files).Avro Download For Windows 10
In the next sections I will use the following example data to demonstrate Avro Tools. You can also download the examplefiles from https://github.com/miguno/avro-cli-examples.
Avro schema
The schema below defines a tuple of
(username, tweet, timestamp)
as the format of our example data records.File:
twitter.avsc
:Data records in JSON format
And here is some corresponding example data with two records that follow the schema defined in the previous section.We store this data in the file
twitter.json
.Example data in
twitter.json
in JSON format:JSON to binary Avro
![Keyboard Keyboard](https://vip-mods.com/uploads/posts/2019-03/1551792132_nazvaniya.jpg)
Without compression:
With Snappy compression:
Note for Mac OS X users: If you run into SnappyError: [FAILED_TO_LOAD_NATIVE_LIBRARY] when trying to compress thedata with Snappy make sure you use JDK 6 and not JDK 7.
Binary Avro to JSON
The same command will work on both uncompressed and compressed data.
Note for Mac OS X users: If you run into SnappyError: [FAILED_TO_LOAD_NATIVE_LIBRARY] when trying to decompressthe data with Snappy make sure you use JDK 6 and not JDK 7.
Retrieve Avro schema from binary Avro
The same command will work on both uncompressed and compressed data.
If you happen to use JDK 7 on Mac OS X 10.8 you will run into the error below when trying to run the Snappy relatedcommands above. In that case make sure to explicitly use JDK 6. On Mac OS 10.8 the JDK 6
java
binary is by defaultavailable at /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/java.The cause of this problem is documented in the bug reportNative (Snappy) library loading fails on openjdk7u4 for mac. This bugis already fixed in the latest Snappy-Java 1.5 milestone releases, but Avro 1.7.4 still depends on the latest stablerelease of Snappy-Java which is 1.0.4.1 (see
lang/java/pom.xml
in the Avro source code).I also found that one way to fix this problem when writing your own Java code is to explicitly require Snappy 1.5.x.Here is the relevant dependency declaration for
build.gradle
in case you are using Gradle. This seems to solvethe problem, but I have yet to confirm whether this is a safe way for production scenarios.Detailed error message:
The example commands above show just a few variants of how to use Avro Tools to read, write and convert Avro files.The Avro Tools library is documented at:
That said I found those docs not that helpful (the sources are however). I’d recommend to just try running the commandline tools without parameters and have a look at their usage instructions which they will print to
STDOUT
. Normallythis is enough to understand how they should be used. Interested in more? You can subscribe to this blog and follow me on Twitter.