From 3b5bca50d5be1259caf19cd4c1f67aaa088f09bf Mon Sep 17 00:00:00 2001
From: Luca Milanesio <luca.milanesio@gmail.com>
Date: Sat, 2 Oct 2021 00:50:29 +0100
Subject: Reuse the same Repository when listing changes by status

Certain queries for multiple changes based on status
need to read the change meta-data from NoteDb on the same
repository. Do not re-open the same repository over and over
again but rather reuse the same in-memory Repository object
with consequent saving in CPU and lowering the systemload
during the execution of change queries.

The existing loading of multiple change notes without passing
the Repository object as parameter is kept for backward
compatibility and can be safely removed on master because
no more referenced by the Gerrit code-base.

Change-Id: I683a1b0cd4dcc64e191df6777dfce059745d5ce9
---
 .../google/gerrit/server/notedb/ChangeNotes.java   | 27 +++++++++++++++++++++-
 .../server/query/change/InternalChangeQuery.java   |  1 +
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/java/com/google/gerrit/server/notedb/ChangeNotes.java b/java/com/google/gerrit/server/notedb/ChangeNotes.java
index 8eb5c5cdaa..047aa0c16a 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotes.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotes.java
@@ -66,12 +66,14 @@ import com.google.inject.Singleton;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
@@ -198,13 +200,14 @@ public class ChangeNotes extends AbstractChangeNotes<ChangeNotes> {
     }
 
     public List<ChangeNotes> create(
+        Repository repo,
         Project.NameKey project,
         Collection<Change.Id> changeIds,
         Predicate<ChangeNotes> predicate) {
       List<ChangeNotes> notes = new ArrayList<>();
       for (Change.Id cid : changeIds) {
         try {
-          ChangeNotes cn = create(project, cid);
+          ChangeNotes cn = create(repo, project, cid);
           if (cn.getChange() != null && predicate.test(cn)) {
             notes.add(cn);
           }
@@ -217,6 +220,28 @@ public class ChangeNotes extends AbstractChangeNotes<ChangeNotes> {
       return notes;
     }
 
+    /* TODO: This is now unused in the Gerrit code-base, however it is kept in the code
+    /* because it is a public method in a stable branch.
+     * It can be removed in master branch where we have more flexibility to change the API
+     * interface.
+     */
+    public List<ChangeNotes> create(
+        Project.NameKey project,
+        Collection<Change.Id> changeIds,
+        Predicate<ChangeNotes> predicate) {
+      try (Repository repo = args.repoManager.openRepository(project)) {
+        return create(repo, project, changeIds, predicate);
+      } catch (RepositoryNotFoundException e) {
+        // The repository does not exist, hence it does not contain
+        // any change.
+      } catch (IOException e) {
+        logger.atWarning().withCause(e).log(
+            "Unable to open project=%s when trying to retrieve changeId=%s from NoteDb",
+            project, changeIds);
+      }
+      return Collections.emptyList();
+    }
+
     public ListMultimap<Project.NameKey, ChangeNotes> create(Predicate<ChangeNotes> predicate)
         throws IOException {
       ListMultimap<Project.NameKey, ChangeNotes> m =
diff --git a/java/com/google/gerrit/server/query/change/InternalChangeQuery.java b/java/com/google/gerrit/server/query/change/InternalChangeQuery.java
index 6605c23da2..1012f4a54e 100644
--- a/java/com/google/gerrit/server/query/change/InternalChangeQuery.java
+++ b/java/com/google/gerrit/server/query/change/InternalChangeQuery.java
@@ -193,6 +193,7 @@ public class InternalChangeQuery extends InternalQuery<ChangeData, InternalChang
 
     List<ChangeNotes> notes =
         notesFactory.create(
+            repo,
             branch.project(),
             changeIds,
             cn -> {
-- 
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