From 9594ab3ac01c3449fde8163d44c9c27261585c9f Mon Sep 17 00:00:00 2001
From: Cao Manh Dat <datcm@apache.org>
Date: Tue, 13 Oct 2020 18:05:33 +0700
Subject: [PATCH] SOLR-14776: Precompute the fingerprint during PeerSync
 (#1814)

After heavy indexing, the call to compute fingerprint takes awhile and slows the leader election. This commit computes the fingerprint in parallel with fetching the fingerprint from the other replicas.

Co-authored-by: Shalin Shekhar Mangar <shalin@apache.org>
---
 solr/CHANGES.txt                              |  3 ++
 .../java/org/apache/solr/update/PeerSync.java | 30 +++++++++++--------
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 58cc0ed0c94..76f85532a90 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -211,6 +211,9 @@ Optimizations
 
 * SOLR-14576 : Do not use SolrCore as keys in a WeakHashMap (noble)
 
+* SOLR-14776: Precompute fingerprint during PeerSync in parallel with fetching fingerprint from replicas.
+  (Cao Manh Dat, Mike Drob via shalin)
+
 Bug Fixes
 ---------------------
 
diff --git a/solr/core/src/java/org/apache/solr/update/PeerSync.java b/solr/core/src/java/org/apache/solr/update/PeerSync.java
index c23bfb1094d..57e78760b01 100644
--- a/solr/core/src/java/org/apache/solr/update/PeerSync.java
+++ b/solr/core/src/java/org/apache/solr/update/PeerSync.java
@@ -267,7 +267,18 @@ public class PeerSync implements SolrMetricProducer {
     for (String replica : replicas) {
       requestFingerprint(replica);
     }
-    
+
+    // We only compute fingerprint during leader election. Therefore after heavy indexing,
+    // the call to compute fingerprint takes awhile and slows the leader election.
+    // So we do it in parallel with fetching the fingerprint from the other replicas
+    IndexFingerprint ourFingerprint;
+    try {
+      ourFingerprint = IndexFingerprint.getFingerprint(core, Long.MAX_VALUE);
+    } catch (IOException e) {
+      log.warn("Could not confirm if we are already in sync. Continue with PeerSync");
+      return false;
+    }
+
     for (;;) {
       ShardResponse srsp = shardHandler.takeCompletedOrError();
       if (srsp == null) break;
@@ -281,19 +292,14 @@ public class PeerSync implements SolrMetricProducer {
         log.warn("Replica did not return a fingerprint - possibly an older Solr version or exception");
         continue;
       }
-      
-      try {
-        IndexFingerprint otherFingerprint = IndexFingerprint.fromObject(replicaFingerprint);
-        IndexFingerprint ourFingerprint = IndexFingerprint.getFingerprint(core, Long.MAX_VALUE);
-        if(IndexFingerprint.compare(otherFingerprint, ourFingerprint) == 0) {
-          log.info("We are already in sync. No need to do a PeerSync ");
-          return true;
-        }
-      } catch(IOException e) {
-        log.warn("Could not confirm if we are already in sync. Continue with PeerSync");
+
+      IndexFingerprint otherFingerprint = IndexFingerprint.fromObject(replicaFingerprint);
+      if(IndexFingerprint.compare(otherFingerprint, ourFingerprint) == 0) {
+        log.info("We are already in sync. No need to do a PeerSync ");
+        return true;
       }
     }
-    
+
     return false;
   }