{"id": "internals:internals-tracer-trace-child-tasks", "page": "internals", "ref": "internals-tracer-trace-child-tasks", "title": "Tracing child tasks", "content": "If your code uses a mechanism such as  asyncio.gather()  to execute code in additional tasks you may find that some of the traces are missing from the display. \n                 You can use the  trace_child_tasks()  context manager to ensure these child tasks are correctly handled. \n                 from datasette import tracer\n\nwith tracer.trace_child_tasks():\n    results = await asyncio.gather(\n        # ... async tasks here\n    ) \n                 This example uses the  register_routes()  plugin hook to add a page at  /parallel-queries  which executes two SQL queries in parallel using  asyncio.gather()  and returns their results. \n                 from datasette import hookimpl\nfrom datasette import tracer\n\n\n@hookimpl\ndef register_routes():\n    async def parallel_queries(datasette):\n        db = datasette.get_database()\n        with tracer.trace_child_tasks():\n            one, two = await asyncio.gather(\n                db.execute(\"select 1\"),\n                db.execute(\"select 2\"),\n            )\n        return Response.json(\n            {\n                \"one\": one.single_value(),\n                \"two\": two.single_value(),\n            }\n        )\n\n    return [\n        (r\"/parallel-queries$\", parallel_queries),\n    ] \n                 Note that running parallel SQL queries in this way has  been known to cause problems in the past , so treat this example with caution. \n                 Adding  ?_trace=1  will show that the trace covers both of those child tasks.", "breadcrumbs": "[\"Internals for plugins\", \"datasette.tracer\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette/issues/2189\", \"label\": \"been known to cause problems in the past\"}]"}