Apply the client ID regen mitigation now

Author: badboy

CHANGELOG.md

@@ -6,6 +6,7 @@
   * Stop reporting db file sizes during init phase ([#3331](https://github.com/mozilla/glean/pull/3331))
   * Tiny performance improvement for putting tasks on the dispatcher ([#3318](https://github.com/mozilla/glean/pull/3318))
   * Instrument the case when the `client_id.txt` file does not exist yet ([#3339](https://github.com/mozilla/glean/pull/3339))
+  * When a missing client ID in the database is detected, Glean now restores the backup client ID ([#3334](https://github.com/mozilla/glean/pull/3334))
 
 # v66.1.2 (2025-11-25)
 

docs/dev/core/internal/client_id_recovery.md

@@ -14,8 +14,7 @@ Any inconsistencies in that data compared to the database will be reported
 and, if applicable, the client ID restored.
 
 **Note:** Glean v66.1.0 will only report the inconsistency, but will not restore a recovered client ID.
-This allows us to measure the impact.
-The mitigation will be enabled in a later release ([bug 1996862](https://bugzilla.mozilla.org/show_bug.cgi?id=1996862)).
+From Glean v66.2.0 on we apply the mitigation and restore the client ID.
 
 The exact flow of decisions is depicted in the chart below.
 The implementation is in [`glean-core/src/core/mod.rs`](https://github.com/mozilla/glean/blob/HEAD/glean-core/src/core/mod.rs#L264)

glean-core/rlb/tests/health_ping_file_overwrite.rs

@@ -79,7 +79,6 @@ fn test_pre_post_init_health_pings_exist() {
     let exception_uuid = &payload["metrics"]["uuid"]["glean.health_recovered_client_id"];
     assert_eq!(&JsonValue::Null, exception_uuid);
 
-    // TODO(bug 1996862): We don't run the mitigation yet.
-    //let ping_client_id = &payload["client_info"]["client_id"];
-    //assert_eq!(client_id, ping_client_id);
+    let ping_client_id = &payload["client_info"]["client_id"];
+    assert_eq!(client_id, ping_client_id);
 }

glean-core/src/core/mod.rs

@@ -359,6 +359,10 @@ impl Glean {
                         .set_sync(&glean, ExceptionState::EmptyDb);
 
                     // state (e) -- mitigation: store recovered client ID in DB
+                    glean
+                        .core_metrics
+                        .client_id
+                        .set_from_uuid_sync(&glean, stored_client_id);
                 } else {
                     let db_client_id = glean
                         .core_metrics
@@ -375,6 +379,10 @@ impl Glean {
                                 .set_sync(&glean, ExceptionState::RegenDb);
 
                             // state (e) -- mitigation: store recovered client ID in DB
+                            glean
+                                .core_metrics
+                                .client_id
+                                .set_from_uuid_sync(&glean, stored_client_id);
                         }
                         Some(db_client_id) if db_client_id == *KNOWN_CLIENT_ID => {
                             // state (i)
@@ -392,6 +400,10 @@ impl Glean {
 
                             // If we have a recovered client ID we also overwrite the database.
                             // state (e)
+                            glean
+                                .core_metrics
+                                .client_id
+                                .set_from_uuid_sync(&glean, stored_client_id);
                         }
                         Some(db_client_id) if db_client_id == stored_client_id => {
                             // all valid. nothing to do

glean-core/tests/clientid_textfile.rs

@@ -71,9 +71,8 @@ fn reused_clientid_from_file() {
     write_clientid_to_file(temp.path(), &new_uuid).unwrap();
 
     let (glean, temp) = new_glean(Some(temp));
-    // TODO(bug 1996862): We don't run the mitigation yet
-    //let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
-    //assert_eq!(new_uuid, db_client_id);
+    let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
+    assert_eq!(new_uuid, db_client_id);
 
     glean.submit_ping_by_name("health", Some("pre_init"));
     let mut pending = get_queued_pings(temp.path()).unwrap();
@@ -141,10 +140,8 @@ fn clientid_regen_issue_with_existing_db() {
 
     let (glean, temp) = new_glean(Some(temp));
 
-    // TODO(bug 1996862): We don't run the mitigation yet
-    _ = file_client_id;
-    //let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
-    //assert_eq!(file_client_id, db_client_id);
+    let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
+    assert_eq!(file_client_id, db_client_id);
 
     glean.submit_ping_by_name("health", Some("pre_init"));
     let mut pending = get_queued_pings(temp.path()).unwrap();
@@ -225,10 +222,8 @@ fn c0ffee_in_db_gets_overwritten_by_stored_client_id() {
 
     let (glean, temp) = new_glean(Some(temp));
 
-    // TODO(bug 1996862): We don't run the mitigation yet
-    _ = file_client_id;
-    //let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
-    //assert_eq!(file_client_id, db_client_id);
+    let db_client_id = clientid_metric().get_value(&glean, None).unwrap();
+    assert_eq!(file_client_id, db_client_id);
 
     glean.submit_ping_by_name("health", Some("pre_init"));
     let mut pending = get_queued_pings(temp.path()).unwrap();
@@ -244,10 +239,9 @@ fn c0ffee_in_db_gets_overwritten_by_stored_client_id() {
     let exception_uuid = &payload["metrics"]["uuid"]["glean.health.recovered_client_id"].as_str();
     assert_eq!(&Some(file_client_id), exception_uuid);
 
-    // TODO(bug 1996862): We don't run the mitigation yet
-    //let exception_uuid = &payload["client_info"]["client_id"].as_str();
-    //assert_eq!(&Some(file_client_id), exception_uuid);
-    // instead we ensure we don't see the c0ffee ID either.
+    let exception_uuid = &payload["client_info"]["client_id"].as_str();
+    assert_eq!(&Some(file_client_id), exception_uuid);
+    // We ensure we don't see the c0ffee ID either.
     let client_id = payload["client_info"]["client_id"].as_str().unwrap();
     assert_ne!("c0ffeec0-ffee-c0ff-eec0-ffeec0ffeec0", client_id);
 }