If Eclipse crashes or is shut down before you end your debugging
session, your session is orphaned. You can’t start a new session until you remove the
orphan. But don’t panic! You can kill an orphaned session in Setup or with the Tooling API.
Kill a Debugging Session in Setup From the Apex Debugger page in Setup, you can easily kill any debugging session in your org—even sessions belonging to your coworkers. Please use this power compassionately!
Kill a Debugging Session with the Tooling API If you’re too cool for declarative tools, fret not: You can kill a debugging session using the Tooling API, without going anywhere near the Setup tree.
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