safekeeper: special error if a timeline has been deleted (#12155)

We might delete timelines on safekeepers before we are deleting them on
pageservers. This should be an exceptional situation, but can occur. As
the first step to improve behaviour here, emit a special error that is
less scary/obscure than "was not found in global map".

It is for example emitted when the pageserver tries to run
`IDENTIFY_SYSTEM` on a timeline that has been deleted on the safekeeper.

Found when analyzing the failure of
`test_scrubber_physical_gc_timeline_deletion` when enabling
`--timelines-onto-safekeepers` on the pytests.

Due to safekeeper restarts, there is no hard guarantee that we will keep
issuing this error, so we need to think of something better if we start
encountering this in staging/prod. But I would say that the introduction
of `--timelines-onto-safekeepers` in the pytests and into staging won't
change much about this: we are already deleting timelines from there. In
`test_scrubber_physical_gc_timeline_deletion`, we'd just be leaking the
timeline before on the safekeepers.

Part of #11712

safekeeper/src/timeline.rs

@@ -395,6 +395,8 @@ pub enum TimelineError {
     Cancelled(TenantTimelineId),
     #[error("Timeline {0} was not found in global map")]
     NotFound(TenantTimelineId),
+    #[error("Timeline {0} has been deleted")]
+    Deleted(TenantTimelineId),
     #[error("Timeline {0} creation is in progress")]
     CreationInProgress(TenantTimelineId),
     #[error("Timeline {0} exists on disk, but wasn't loaded on startup")]

safekeeper/src/timelines_global_map.rs

@@ -78,7 +78,13 @@ impl GlobalTimelinesState {
             Some(GlobalMapTimeline::CreationInProgress) => {
                 Err(TimelineError::CreationInProgress(*ttid))
             }
-            None => Err(TimelineError::NotFound(*ttid)),
+            None => {
+                if self.has_tombstone(ttid) {
+                    Err(TimelineError::Deleted(*ttid))
+                } else {
+                    Err(TimelineError::NotFound(*ttid))
+                }
+            }
         }
     }
 

test_runner/regress/test_safekeeper_deletion.py

@@ -30,6 +30,7 @@ def test_safekeeper_delete_timeline(neon_env_builder: NeonEnvBuilder, auth_enabl
     env.pageserver.allowed_errors.extend(
         [
             ".*Timeline .* was not found in global map.*",
+            ".*Timeline .* has been deleted.*",
             ".*Timeline .* was cancelled and cannot be used anymore.*",
         ]
     )
@@ -198,6 +199,7 @@ def test_safekeeper_delete_timeline_under_load(neon_env_builder: NeonEnvBuilder)
         env.pageserver.allowed_errors.extend(
             [
                 ".*Timeline.*was cancelled.*",
+                ".*Timeline.*has been deleted.*",
                 ".*Timeline.*was not found.*",
             ]
         )

test_runner/regress/test_wal_acceptor.py

@@ -433,6 +433,7 @@ def test_wal_backup(neon_env_builder: NeonEnvBuilder):
     env.pageserver.allowed_errors.extend(
         [
             ".*Timeline .* was not found in global map.*",
+            ".*Timeline .* has been deleted.*",
             ".*Timeline .* was cancelled and cannot be used anymore.*",
         ]
     )
@@ -1934,6 +1935,7 @@ def test_membership_api(neon_env_builder: NeonEnvBuilder):
     env.pageserver.allowed_errors.extend(
         [
             ".*Timeline .* was not found in global map.*",
+            ".*Timeline .* has been deleted.*",
             ".*Timeline .* was cancelled and cannot be used anymore.*",
         ]
     )