Logging and debugging
Logging
Everything that logs owns an ILogChannel, and channels form a parent/child tree that mirrors the execution: pipeline, transform, the database connection inside it. That parentage is what lets Hop show the log of one transform separately from the pipeline it ran in.
Seven levels, from LogLevel:
NOTHING, ERROR, MINIMAL, BASIC, DETAILED, DEBUG, ROWLEVEL
The level is set per run, and a channel logs only what its level allows. ROWLEVEL logs per row and is a debugging tool, not something to leave on.
Where the log lines end up
HopLogStore is the central store every channel appends to. It is initialized by HopEnvironment.init(), so nothing is captured before that call.
Every runtime object — IPipelineEngine, IWorkflowEngine, a transform, a database connection — owns a log channel id, and that id is the key into the store. The parent/child relations between those channels live in LoggingRegistry.getInstance().
To read back what an object logged, ask the store’s appender for that channel’s buffer:
String logText =
HopLogStore.getInstance().getAppender().getBuffer(pipeline.getLogChannelId(), true);The second argument clears the buffer as it is read. This is the same path a logBasic() call from a User Defined Java Class takes: the transform’s own channel, the same store.
Attaching a debugger
The launcher scripts in the distribution read HOP_OPTIONS, and each ships with a commented-out JDWP line:
HOP_OPTIONS="${HOP_OPTIONS} -Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=5009"Uncomment it, or export HOP_OPTIONS yourself, and attach a remote debugger to that port. This works for hop-gui, hop-run, hop-server and the rest of the scripts.
For running Hop straight from the IDE instead, see Setting up your development environment.
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