Migration Guide

Changes from 1.3.x to 1.4.x

• Addition of HystrixObservableCommand. See #321 for full description of design
• Timeouts now apply to semaphore-isolated commands as well as thread-isolated commands. Before 1.4.x, semaphore-isolated commands could not timeout. They now have a timeout registered on another (HystrixTimer) thread, which triggers the timeout flow. If you use semaphore-isolated commands, they will now see timeouts. As all HystrixCommands have a default timeout, this potentially affects all semaphore-isolated commands.
• Timeouts now fire on HystrixCommand.queue(), even if the caller never calls get() on the resulting Future. Before 1.4.x, only calls to get() triggered the timeout mechanism to take effect.
• Execution hooks changed to more closely match the Observable model. The hooks from 1.3 still exist and still get invoked, but are now deprecated. See https://github.com/Netflix/Hystrix/issues/682 for all the details
• Execution Hooks that generate BadRequestExceptions now behave the same as if a command generated it (i.e. fallback/metrics are skipped)
• Addition of metrics
  • command metrics for bad request, max concurrent requests, number of emissions, number of fallback emissions
  • thread pool metrics for number of thread pool-rejections
  • collapser metrics for number of commands collapsed, number of batches, size of batches, size of shards
• Added EMIT and FALLBACK_EMIT event types that will show up in the HystrixRequestLog for HystrixObservableCommands. These show how many items are in the streams of data produced by the commands
• Upgraded to Java7 (1.4.0/1.4.1/1.4.2 were built with Java 7, but 1.4.3+ rolled back to Java 6)
• Upgraded to RxJava 1.0.x (1.0.7 currently)

(Proposed) changes from 1.4.x to 1.5.x

• Remove deprecated hooks #684
• Scalar asynchronous command #602