commit bd185bbac4275299a587eae67eae58f856052a93
Author: jcoleman <james.coleman@getbraintree.com>
Date:   Sun Jun 23 19:13:09 2019 +0000

    Correct assertion comment in tuplesort_set_bound
    
    The implementation of puttuple_common keeps the state TSS_INITIAL
    while tuples are inserted unless we reach a point where we decide
    to transition to a different mode and set the state to TSS_BOUNDED
    or TSS_BUILDRUNS.
    
    Therefore it's not true that the assertion guards against having loaded
    any tuples; rather it guarantees that we remain in standard memory
    quicksort mode.

diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index 7b8e67899e..c108bd4513 100644
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -1185,7 +1185,9 @@ tuplesort_begin_datum(Oid datumType, Oid sortOperator, Oid sortCollation,
 void
 tuplesort_set_bound(Tuplesortstate *state, int64 bound)
 {
-	/* Assert we're called before loading any tuples */
+	/*
+	 * Assert we're still in memory quicksort mode and haven't transitioned to
+	 * heap or tape mode. */
 	Assert(state->status == TSS_INITIAL);
 	Assert(state->memtupcount == 0);
 	Assert(!state->bounded);