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postgresqllibpq

postgres libpq: synchronous COPY mysteriously cancelled "due to user request"

My application is using libpq to write data to Postgres using the COPY API. After over 900000 successful COPY+commit (each containing a single row, don't ask) actions, one errored out with the following:

ERROR: canceling statement due to user request
CONTEXT: COPY [...]

My code never calls PQcancel or related friends, which I think is precluded anyway by the fact that libpq is being used synchronously and my app is not multi-threaded.

  • libpq v8.3.0
  • Postgres v9.2.4

Is there any reasonable explanation for what might have caused the COPY to be cancelled? Will upgrading libpq (as I have done in more recent versions of my application) be expected to improve the situation?

The customer reports that the Postgres server may have been shut down when this error was reported, but I'm not convinced since the error text is pretty specific.

Solution

  • That error will be emitted when you:

    • send a PQcancel
    • use pg_cancel_backend
    • Hit control-C in psql (which invokes PQcancel)
    • Send SIGINT to a backend, e.g. kill -INT or kill -2.

    My initial answer was incorrect, claiming that the following also produced the same error. They don't; these:

    • pg_terminate_backend
    • pg_ctl shutdown -m fast

    will emit a different error FATAL: terminating connection due to administrator command.