Create unique ids even for random conflicts

With this commit we ensure that generated ids are always unique, even
when generating random conflicts for bulk requests. The general strategy
to simulate conflicts is as follows:

1. Generate a list of ids upfront.
2. Iterate through this list and pick a duplicate in 25% of all cases.

In order to avoid accidentally creating more conflicts than expected,
the list of ids generated in step one, needs to contain unique ids.
However, we create ids at random without considering which ids have
already been generated. This is now changed by first generating all ids
and then shuffling them.

Relates #476

esrally/track/params.py

@@ -581,17 +581,16 @@ def number_of_bulks(corpora, partition_index, total_partitions, bulk_size):
     return bulks
 
 
-def build_conflicting_ids(conflicts, docs_to_index, offset, rand=random.randint):
+def build_conflicting_ids(conflicts, docs_to_index, offset, shuffle=random.shuffle):
     if conflicts is None or conflicts == IndexIdConflict.NoConflicts:
         return None
     logger.info("building ids with id conflicts of type [%s]" % conflicts)
     all_ids = [0] * docs_to_index
     for i in range(docs_to_index):
         # always consider the offset as each client will index its own range and we don't want uncontrolled conflicts across clients
-        if conflicts == IndexIdConflict.SequentialConflicts:
-            all_ids[i] = "%10d" % (offset + i)
-        else:  # RandomConflicts
-            all_ids[i] = "%10d" % rand(offset, offset + docs_to_index)
+        all_ids[i] = "%10d" % (offset + i)
+    if conflicts == IndexIdConflict.RandomConflicts:
+        shuffle(all_ids)
     return all_ids
 
 

tests/track/params_test.py

@@ -80,22 +80,24 @@ def test_sequential_conflicts(self):
         )
 
     def test_random_conflicts(self):
+        predictable_shuffle = list.reverse
+
         self.assertEqual(
             [
-                "         3",
-                "         3",
-                "         3"
+                "         2",
+                "         1",
+                "         0"
             ],
-            params.build_conflicting_ids(params.IndexIdConflict.RandomConflicts, 3, 0, rand=lambda x, y: y)
+            params.build_conflicting_ids(params.IndexIdConflict.RandomConflicts, 3, 0, shuffle=predictable_shuffle)
         )
 
         self.assertEqual(
             [
-                "         8",
-                "         8",
-                "         8"
+                "         7",
+                "         6",
+                "         5"
             ],
-            params.build_conflicting_ids(params.IndexIdConflict.RandomConflicts, 3, 5, rand=lambda x, y: y)
+            params.build_conflicting_ids(params.IndexIdConflict.RandomConflicts, 3, 5, shuffle=predictable_shuffle)
         )