Set PerThreadCache as readonly when formatting change JSON

Apply the same optimisation made for Change-Id: I1b71bfcf to
the formatting of change JSON output as return value for REST APIs.

The ChangeJson class needs to read multiple fields from NoteDb
and calls the /meta refs lookups multiple times for the same
change JSON output (e.g. formatting the output JSON of an
abandoned change generates 23 refs lookups calls for a single
change).

The same considerations of performance improvement and reduction
of /meta refs lookup are valid in this use-case.

Release-Notes: enable the read-only cache of /meta when producing JSON
Change-Id: Ic0e747352dcd8a0c2c1348a9878a5a4165777abd

1 files changed, 4 insertions, 1 deletions

diff --git a/java/com/google/gerrit/server/change/ChangeJson.java b/java/com/google/gerrit/server/change/ChangeJson.java
index 2aaf4c513c..af557cef18 100644
--- a/java/com/google/gerrit/server/change/ChangeJson.java
+++ b/java/com/google/gerrit/server/change/ChangeJson.java
@@ -84,6 +84,8 @@ import com.google.gerrit.server.ReviewerStatusUpdate;
 import com.google.gerrit.server.StarredChangesUtil;
 import com.google.gerrit.server.account.AccountInfoComparator;
 import com.google.gerrit.server.account.AccountLoader;
+import com.google.gerrit.server.cache.PerThreadCache;
+import com.google.gerrit.server.cache.PerThreadCache.ReadonlyRequestWindow;
 import com.google.gerrit.server.config.TrackingFooters;
 import com.google.gerrit.server.index.change.ChangeField;
 import com.google.gerrit.server.notedb.ChangeNotes;
@@ -493,7 +495,8 @@ public class ChangeJson {
       ChangeData cd, Optional<PatchSet.Id> limitToPsId, Supplier<I> changeInfoSupplier)
       throws PatchListNotAvailableException, GpgException, OrmException, PermissionBackendException,
           IOException {
-    try (Timer0.Context ignored = metrics.toChangeInfoLatency.start()) {
+    try (Timer0.Context ignored = metrics.toChangeInfoLatency.start();
+        ReadonlyRequestWindow window = PerThreadCache.openReadonlyRequestWindow()) {
       return toChangeInfoImpl(cd, limitToPsId, changeInfoSupplier);
     }
   }