Re: anti-join chosen even when slower than old plan

"Kevin Grittner" <Kevin.Grittner@wicourts.gov> wrote:

> samples  %        symbol name
> 2320174  33.7617  index_getnext

I couldn't resist seeing where the time went within this function.
Over 13.7% of the opannotate run time was on this bit of code:

  /*
   * The xmin should match the previous xmax value, else chain is
   * broken.  (Note: this test is not optional because it protects
   * us against the case where the prior chain member's xmax aborted
   * since we looked at it.)
   */
  if (TransactionIdIsValid(scan->xs_prev_xmax) &&
      !TransactionIdEquals(scan->xs_prev_xmax,
                        HeapTupleHeaderGetXmin(heapTuple->t_data)))
      break;

I can't see why it would be such a hotspot, but it is.

-Kevin