From 1abbca37c4c320bafbbaad8cd4d4155372526a86 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Sun, 21 Feb 2021 19:14:28 +0100
Subject: [PATCH] Add adapted version of maglev for multi-dc

---
 script/simulate_ring.py | 78 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/script/simulate_ring.py b/script/simulate_ring.py
index 2e1c54564..611f2c985 100644
--- a/script/simulate_ring.py
+++ b/script/simulate_ring.py
@@ -60,7 +60,7 @@ def method1(nodes):
 
 
 def method2(nodes):
-    partition_bits = 10
+    partition_bits = 8
     partitions = list(range(2**partition_bits))
     def partition_node(i):
         h, hn, hndc = None, None, None
@@ -92,7 +92,7 @@ def method2(nodes):
 
 
 def method3(nodes):
-    partition_bits = 10
+    partition_bits = 8
 
     queues = []
     for (node_id, node_dc, n_tokens) in nodes:
@@ -130,6 +130,62 @@ def method3(nodes):
     return walk_ring
 
 
+
+def method4(nodes):
+    partition_bits = 8
+    max_replicas = 3
+
+    partitions = [[] for _ in range(2**partition_bits)]
+    dcs = list(set(node_dc for _, node_dc, _ in nodes))
+
+    # Maglev, improved for several replicas on several DCs
+    for ri in range(max_replicas):
+        queues = []
+        for (node_id, node_dc, n_tokens) in nodes:
+            que = [(i, hash_str(f"{node_id} {i}")) for i in range(2**partition_bits)]
+            que.sort(key=lambda x: x[1])
+            que = [x[0] for x in que]
+            queues.append((node_id, node_dc, n_tokens, que))
+
+        queues.sort(key=lambda x: hash_str("{} {}".format(ri, x[0])))
+
+        remaining = 2**partition_bits
+        while remaining > 0:
+            for toktok in range(100):
+                for iq in range(len(queues)):
+                    node_id, node_dc, n_tokens, node_queue = queues[iq]
+                    if toktok >= n_tokens:
+                        continue
+                    for qi, qv in enumerate(node_queue):
+                        if len(partitions[qv]) != ri:
+                            continue
+                        p_dcs = set([x[0] for x in partitions[qv]])
+                        p_nodes = [x[1] for x in partitions[qv]]
+                        if node_dc not in p_dcs or (len(p_dcs) == len(dcs) and node_id not in p_nodes):
+                            partitions[qv].append((node_dc, node_id))
+                            remaining -= 1
+                            queues[iq] = (node_id, node_dc, n_tokens, node_queue[qi+1:])
+                            break
+
+    # count
+    tokens_of_node = {}
+    for nodelist in partitions:
+        for node_dc, node_id in nodelist:
+            if node_id not in tokens_of_node:
+                tokens_of_node[node_id] = 0
+            tokens_of_node[node_id] += 1
+    print("#tokens per node:")
+    for node, ntok in sorted(list(tokens_of_node.items())):
+        print(node, ": ", ntok)
+
+    def walk_ring(v, rep):
+        vh = hashlib.sha256(v.encode('ascii')).digest()
+        i = (vh[0]<<8 | vh[1]) % (2**partition_bits)
+        assert len(set([node_dc for node_dc, _ in partitions[i]])) == min(max_replicas, len(dcs))
+        return [node_id for _, node_id in partitions[i]]
+
+    return walk_ring
+
 def evaluate_method(walk_ring):
     node_data_counts = {}
     for i in range(100000):
@@ -175,3 +231,21 @@ if __name__ == "__main__":
              ]
     method3_walk_ring = method3(nodes)
     evaluate_method(method3_walk_ring)
+
+
+    print("------")
+    print("method 4 (maglev, multi-dc twist)")
+    nodes = [('digitale', 'atuin', 8),
+             ('drosera', 'atuin', 8),
+             ('datura', 'atuin', 8),
+             ('io', 'jupiter', 16),
+             ('mini', 'grog', 4),
+             ('mixi', 'grog', 4),
+             ('moxi', 'grog', 4),
+             ('modi', 'grog', 4),
+             ('geant', 'grisou', 16),
+             ('gipsie', 'grisou', 16),
+             #('isou', 'jupiter', 8),
+             ]
+    method4_walk_ring = method4(nodes)
+    evaluate_method(method4_walk_ring)