Fix typos and improve incremental sort comments

Author: Justin Pryzby, James Coleman
Discussion: https://postgr.es/m/20200419023625.GP26953@telsasoft.com

src/backend/commands/explain.c

@@ -2869,7 +2869,7 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 }
 
 /*
- * If it's EXPLAIN ANALYZE, show tuplesort stats for a incremental sort node
+ * If it's EXPLAIN ANALYZE, show tuplesort stats for an incremental sort node
  */
 static void
 show_incremental_sort_info(IncrementalSortState *incrsortstate,
@@ -2917,7 +2917,7 @@ show_incremental_sort_info(IncrementalSortState *incrsortstate,
 			&incrsortstate->shared_info->sinfo[n];
 
 			/*
-			 * If a worker hasn't process any sort groups at all, then exclude
+			 * If a worker hasn't processed any sort groups at all, then exclude
 			 * it from output since it either didn't launch or didn't
 			 * contribute anything meaningful.
 			 */

src/backend/executor/nodeIncrementalSort.c

@@ -1152,8 +1152,10 @@ ExecReScanIncrementalSort(IncrementalSortState *node)
 	/*
 	 * If we've set up either of the sort states yet, we need to reset them.
 	 * We could end them and null out the pointers, but there's no reason to
-	 * repay the setup cost, and because guard setting up pivot comparator
-	 * state similarly, doing so might actually cause a leak.
+	 * repay the setup cost, and because ExecIncrementalSort guards
+	 * presorted column functions by checking to see if the full sort state
+	 * has been initialized yet, setting the sort states to null here might
+	 * actually cause a leak.
 	 */
 	if (node->fullsort_state != NULL)
 	{

src/backend/utils/sort/tuplesort.c

@@ -1428,11 +1428,11 @@ tuplesort_updatemax(Tuplesortstate *state)
 	}
 
 	/*
-	 * Sort evicts data to the disk when it didn't manage to fit those data to
-	 * the main memory.  This is why we assume space used on the disk to be
+	 * Sort evicts data to the disk when it wasn't able to fit that data into
+	 * main memory.  This is why we assume space used on the disk to be
 	 * more important for tracking resource usage than space used in memory.
-	 * Note that amount of space occupied by some tuple set on the disk might
-	 * be less than amount of space occupied by the same tuple set in the
+	 * Note that the amount of space occupied by some tupleset on the disk might
+	 * be less than amount of space occupied by the same tupleset in
 	 * memory due to more compact representation.
 	 */
 	if ((isSpaceDisk && !state->isMaxSpaceDisk) ||