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From: Marcelo Fernandes <[email protected]>
To: [email protected]
Subject: Resetting the lock_timeout value for a transaction
Date: Mon, 28 Apr 2025 11:28:41 +1200
Message-ID: <CAM2F1VM86387XCtNgbTbVQO6PfYBjCHg74XLsfavWJ-o-OZE+Q@mail.gmail.com> (raw)

Hi folks,

I have been using:

  -- Setting the SESSION lock timeout to 10 seconds
  SET lock_timeout = '10s';

  -- Setting the TRANSACTION lock timeout to 20 seconds
  BEGIN;
  SET LOCAL lock_timeout = '20s';
  COMMIT;

However, I have been caught by the behaviour of "RESET lock_timeout;" when
inside and outside a transaction.

  -- Resets the lock_timeout value for the SESSION.
  RESET lock_timeout;

  -- WARNING: This will reset BOTH the SESSION and TRANSACTION lock_timeouts.
  BEGIN;
  SET LOCAL lock_timeout = '20s';
  RESET lock_timeout;
  COMMIT;

I would have expected that the "RESET lock_timeout;" inside a transaction would
only reset the value of lock_timeout for that specific transaction. Or else,
there would be an equivalent "RESET LOCAL lock_timeout;" to be used for that.

But I can't find anything that does just that.
Am I missing something? Example script for convenience:

  -- This is the default lock_timeout (0s)
  SHOW lock_timeout;

  -- Set the SESSION lock timeout (42s)
  SET lock_timeout = '42s';
  SHOW lock_timeout;

  BEGIN;

  -- WARNING: This will set a new value for the SESSION lock_timeout from within
  -- the transaction because it is missing the LOCAL key word!
  SET lock_timeout = '10s';
  SHOW lock_timeout;

  -- Set it again but this time only for the transaction. This value will not
  -- affect the session lock_timeout.
  SET LOCAL lock_timeout = '9s';
  SHOW lock_timeout;

  -- Reset BOTH the SESSION and Transaction lock_timeout (both go back to 0, the
  -- default).
  RESET lock_timeout;
  SHOW lock_timeout;

  COMMIT;

  -- Should now be 0s because it was reset inside the transaction.
  SHOW lock_timeout;

Thanks, Marcelo

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