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

"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)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