This is a very brief tutorial how to get a stream of the Raspberry Pi camera into a browser. The original article can be found here.
I was searching a lot how to stream directly from the camera to the network, yet I did not find a solution. So what we are doing here is using the timelaps feature from raspistill combined with MJPG-Streamer. In the end you will be able to see the stream in a webbrowser or in VLC Media Player.
Continue reading How to enable Camera Streaming on a Raspberry Pi
Last week I ran into a an ugly problem of Scalding:
I needed to read a really large table from MySQL to process it in a certain job. In generall this is trivial: just use a JDBC Source, select your columns and that’s it.
Usually we do this by using 1-3 parallel connections to the SQL-server. This time I started running out of memory because scalding didn’t (more precicely: couldn’t) swap/spill to disk. The problem here is the default behaviour of the mysql-connector. The api docs says:
By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate, and due to the design of the MySQL network protocol is easier to implement. If you are working with ResultSets that have a large number of rows or large values, and can not allocate heap space in your JVM for the memory required, you can tell the driver to stream the results back one row at a time.
So, what does this mean: If you query a 10 GB table, you get all the data and the connector tries to buffer it in memory – which is a bad idea if you just want to process tuple by tuple. You can then split this large query into 10 smaller ones:
SELECT ... FROM ... LIMIT 0, x,
SELECT ... FROM ... LIMIT x+1, y, … etc. This works – but partitioning a large result this way is not very efficient because starting from the second query, MySQL has to iterate over
x rows until it can start gathering and returning results. So you partition the big query into 10 smaller results but you put quite a lot of load to the server. And over all you still have to keep a lot of results in RAM.
Continue reading Enable MySQL Streaming in Cascading / Scalding