fix calculation

stackabletech · Sep 27, 2023 · 2c343d7 · 2c343d7
1 parent 3b9ead0
commit 2c343d7
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Showing 2 changed files with 28 additions and 18 deletions.
diff --git a/docs/modules/zookeeper/pages/usage_guide/operations/pod-disruptions.adoc b/docs/modules/zookeeper/pages/usage_guide/operations/pod-disruptions.adoc
@@ -14,6 +14,12 @@ Taking this into consideration, our operator uses the following algorithm to det
 
 [source,rust]
 ----
+fn quorum_size(num_servers: u16) -> u16 {
+    // Same as max((num_servers / 2) + 1, 1), but without the need for floating point arithmetics,
+    // which are subject to rounding errors.
+    max((num_servers + 2) / 2, 1)
+}
+
 // Minimum required amount of servers to form quorum.
 let quorum_size = quorum_size(num_servers);
 
@@ -26,6 +32,8 @@ let max_unavailable = max(max_unavailable, 1)
 
 This results e.g. in the following numbers:
 
+TIP: It is strongly recommended to use a odd number of servers (e.g. 3, 5 or 7).
+
 [cols="1,1,1"]
 |===
 |Number of servers
@@ -37,42 +45,42 @@ This results e.g. in the following numbers:
 |1
 
 |2
-|1
+|2
 |1
 
 |3
 |2
 |1
 
 |4
-|2
+|3
 |1
 
 |5
 |3
 |1
 
 |6
-|3
-|2
+|4
+|1
 
 |7
 |4
 |2
 
 |8
-|4
-|3
+|5
+|2
 
 |9
 |5
 |3
 
 |10
-|5
-|4
+|6
+|3
 
 |20
-|10
-|9
+|11
+|8
 |===
diff --git a/rust/operator-binary/src/operations/pdb.rs b/rust/operator-binary/src/operations/pdb.rs
@@ -69,7 +69,9 @@ fn max_unavailable_servers(num_servers: u16) -> u16 {
 }
 
 fn quorum_size(num_servers: u16) -> u16 {
-    max((num_servers as f32 / 2.0).ceil() as u16, 1)
+    // Same as max((num_servers / 2) + 1, 1), but without the need for floating point arithmetics,
+    // which are subject to rounding errors.
+    max((num_servers + 2) / 2, 1)
 }
 
 #[cfg(test)]
@@ -80,17 +82,17 @@ mod test {
     #[rstest]
     #[case(0, 1, 1)]
     #[case(1, 1, 1)]
-    #[case(2, 1, 1)]
+    #[case(2, 2, 1)]
     #[case(3, 2, 1)]
-    #[case(4, 2, 1)]
+    #[case(4, 3, 1)]
     #[case(5, 3, 1)]
-    #[case(6, 3, 2)]
+    #[case(6, 4, 1)]
     #[case(7, 4, 2)]
-    #[case(8, 4, 3)]
+    #[case(8, 5, 2)]
     #[case(9, 5, 3)]
-    #[case(10, 5, 4)]
-    #[case(20, 10, 9)]
-    #[case(100, 50, 49)]
+    #[case(10, 6, 3)]
+    #[case(20, 11, 8)]
+    #[case(100, 51, 48)]
 
     fn test_max_unavailable_servers(
         #[case] num_servers: u16,