1 files changed, 45 insertions, 0 deletions
diff --git a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/GlobalBucketSyncStatsCalculator.java b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/GlobalBucketSyncStatsCalculator.java
new file mode 100644
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+++ b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/GlobalBucketSyncStatsCalculator.java
@@ -0,0 +1,45 @@
+// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.clustercontroller.core;
+
+import java.util.Optional;
+
+/**
+ * @author vekterli
+ */
+public class GlobalBucketSyncStatsCalculator {
+
+    /**
+     * Compute a value in [0, 1] representing how much of the cluster's data space is currently
+     * out of sync, i.e. pending merging. In other words, if the value is 1 all buckets are out
+     * of sync, and conversely if it's 0 all buckets are in sync. This number applies across bucket
+     * spaces.
+     *
+     * @param globalStats Globally aggregated content node statistics for the entire cluster.
+     * @return Optional containing a value [0, 1] representing the ratio of buckets pending merge
+     *         in relation to the total number of buckets in the cluster, or an empty optional if
+     *         the underlying global statistics contains invalid/incomplete information.
+     */
+    public static Optional<Double> clusterBucketsOutOfSyncRatio(ContentNodeStats globalStats) {
+        long totalBuckets = 0;
+        long pendingBuckets = 0;
+        for (var space : globalStats.getBucketSpaces().values()) {
+            if (!space.valid()) {
+                return Optional.empty();
+            }
+            totalBuckets   += space.getBucketsTotal();
+            pendingBuckets += space.getBucketsPending();
+        }
+        // It's currently possible for the reported number of pending buckets to be greater than
+        // the number of total buckets. Example: this can happen if a bucket is present on a single
+        // node, but should have been replicated to 9 more nodes. Since counts are not normalized
+        // across content nodes for a given bucket, this will be counted as 9 pending and 1 total.
+        // Eventually this will settle as 0 pending and 10 total.
+        // TODO report node-normalized pending/total counts from distributors and use these.
+        pendingBuckets = Math.min(pendingBuckets, totalBuckets);
+        if (totalBuckets <= 0) {
+            return Optional.of(0.0); // No buckets; cannot be out of sync by definition
+        }
+        return Optional.of((double)pendingBuckets / (double)totalBuckets);
+    }
+
+}