Showing posts from July, 2015

Accessing Chronicle Engine via NFS

Overview Chronicle Engine is a data virtualisation layer.  It abstracts away the complexity of accessing, manipulating and subscribing to various data source so that the user of that data doesn't need to know how or where  the data is actually stored.  This means that this data can be migrated between systems or stored in a manner which is more efficient but would be to complex for the developer to use. The basic interfaces are Concurrent Map and a simple Pub/Sub.  Using these in combination with the stream like filters and transformation you can access files, in memory data caches, LDAP, SQL Databases, Key-value NoSQL databases and low latency persisted stores. What we are investigating is using NFS as a means of access as well as our Java and C# client to access the data in a natural way.  This way any program on Windows, Unix or MacOSX could use it. How might this look? Access via NFS. The data stores in Chronicle Engine are organise hierarchically as a tree, rather li

Is using Unsafe really about speed or functionality?

Overview Around 6 years ago, I started using a class which up to that point was just a curiosity sun.misc.Unsafe .  I had used it for deserialization and re-throwing Exceptions but not used all it's capabilities or talked about it publicly. The first open source library I saw which did use Unsafe in a serious way was Disruptor. This encouraged me that it could be used in a stable library.  About a year later I released my first open source libraries, SharedHashMap (later Chronicle Map) and Chronicle (later Chronicle Queue).  This used Unsafe to access off heap memory in Java 6.  This made a real difference to the performance of off heap memory, but more importantly what I could do with shared memory. i.e. data structures shared across JVMs. But how much difference does it make today? Is using Unsafe always faster? What we are look for is compelling performance differences.  If the difference is not compelling, using the simplest code possible makes more sense. i.e. using na

Using JMH to find the fastest way to encode/decode UTF8

Overview I had played with JMH before however this is the first time I have used JMH to solve a production problem.  I had some idea how to optimise the code involved but trying different combinations with JMH lead to a significant improvement. In this test I am encoding a String as UTF8 to direct memory so it can be written to a TCP socket.  Also I need to take data written to direct memory via an NIO and encode it into a StringBuilder (which can be reused) The tests These tests involved a combination of using reflection to obtain the underlying data structure of String and StringBuilder but also using Unsafe to access the native memory. To my surprise, access String via reflection appeared to be no faster, possibly slower. However @jponge pointed out that I needed to be returning a result from each benchamrk to avoid dead code elimination.  After I did this, the access via reflection was faster. See encode_unsafeLoopCharA t  and encode_unsafeLoopCharAt

How and Why to Serialialize Lambdas

Overview Serializing lambdas can be useful in a number of use cases such as persisting configuration, or as a visitor pattern to remote resources. Remote Visitors For example, so I want to access a resource on a remote Map, I can use get/put, but say I just want to return a field from the value of a Map, I can pass a lambda as a visitor to extract the information I want. MapView userMap =      Chassis. acquireMap ( "users" , String. class , UserInfo. class ); userMap.put( "userid" , new UserInfo( "User's Name" )); // print out changes userInfo.registerSubscriber(System. out ::println); // obtain just the fullName without downloading the whole object String name= userMap.applyToKey( "userid" , u -> u. fullName ); // increment a counter atomically and trigger // an updated event printed with the subscriber. userMap.asyncUpdateKey( "userid" , ui -> {      ui. usageCounter ++;      return ui; }); // increment a