Fix gc after import

pageserver/src/layered_repository.rs

@@ -2210,6 +2210,9 @@ impl LayeredTimeline {
                     LsnForTimestamp::Past(lsn) => {
                         debug!("past({})", lsn);
                     }
+                    LsnForTimestamp::NoData(lsn) => {
+                        debug!("nodata({})", lsn);
+                    }
                 }
                 debug!("pitr_cutoff_lsn = {:?}", pitr_cutoff_lsn)
             }

pageserver/src/page_service.rs

@@ -554,7 +554,7 @@ impl PageServerHandler {
         // Create empty timeline
         info!("creating new timeline");
         let repo = tenant_mgr::get_repository_for_tenant(tenant_id)?;
-        let timeline = repo.create_empty_timeline(timeline_id, Lsn(0))?;
+        let timeline = repo.create_empty_timeline(timeline_id, base_lsn)?;
         let repartition_distance = repo.get_checkpoint_distance();
         let mut datadir_timeline =
             DatadirTimeline::<LayeredRepository>::new(timeline, repartition_distance);
@@ -1151,6 +1151,7 @@ impl postgres_backend::Handler for PageServerHandler {
                 LsnForTimestamp::Present(lsn) => format!("{}", lsn),
                 LsnForTimestamp::Future(_lsn) => "future".into(),
                 LsnForTimestamp::Past(_lsn) => "past".into(),
+                LsnForTimestamp::NoData(_lsn) => "nodata".into(),
             };
             pgb.write_message_noflush(&BeMessage::DataRow(&[Some(result.as_bytes())]))?;
             pgb.write_message(&BeMessage::CommandComplete(b"SELECT 1"))?;

pageserver/src/pgdatadir_mapping.rs

@@ -51,6 +51,7 @@ pub enum LsnForTimestamp {
     Present(Lsn),
     Future(Lsn),
     Past(Lsn),
+    NoData(Lsn),
 }
 
 impl<R: Repository> DatadirTimeline<R> {
@@ -263,7 +264,7 @@ impl<R: Repository> DatadirTimeline<R> {
             (false, false) => {
                 // This can happen if no commit records have been processed yet, e.g.
                 // just after importing a cluster.
-                bail!("no commit timestamps found");
+                Ok(LsnForTimestamp::NoData(max_lsn))
             }
             (true, false) => {
                 // Didn't find any commit timestamps larger than the request

test_runner/batch_others/test_import.py

@@ -191,3 +191,8 @@ def test_import_from_pageserver(test_output_dir, pg_bin, vanilla_pg, neon_env_bu
     # Check it's the same as the first fullbackup
     # TODO pageserver should be checking checksum
     assert os.path.getsize(tar_output_file) == os.path.getsize(new_tar_output_file)
+
+    # Check that gc works
+    psconn = env.pageserver.connect()
+    pscur = psconn.cursor()
+    pscur.execute(f"do_gc {tenant.hex} {timeline} 0")