fix(pageserver): handle lsn lease requests for unnormalized lsns (#9137)

Fixes #9098.

## Problem

See
#9098 (comment).

### Related

A similar problem happened with branch creation, which was discussed
[here](#2143 (comment))
and fixed by #2529.

## Summary of changes

- Normalize the lsn on pageserver side upon lsn lease request, stores
the normalized LSN.

Signed-off-by: Yuchen Liang <[email protected]>

pageserver/src/tenant/timeline.rs

@@ -112,7 +112,7 @@ use pageserver_api::reltag::RelTag;
 use pageserver_api::shard::ShardIndex;
 
 use postgres_connection::PgConnectionConfig;
-use postgres_ffi::to_pg_timestamp;
+use postgres_ffi::{to_pg_timestamp, v14::xlog_utils, WAL_SEGMENT_SIZE};
 use utils::{
     completion,
     generation::Generation,
@@ -1337,6 +1337,10 @@ impl Timeline {
         _ctx: &RequestContext,
     ) -> anyhow::Result<LsnLease> {
         let lease = {
+            // Normalize the requested LSN to be aligned, and move to the first record
+            // if it points to the beginning of the page (header).
+            let lsn = xlog_utils::normalize_lsn(lsn, WAL_SEGMENT_SIZE);
+
             let mut gc_info = self.gc_info.write().unwrap();
 
             let valid_until = SystemTime::now() + length;

test_runner/regress/test_readonly_node.py

@@ -122,6 +122,7 @@ def test_readonly_node_gc(neon_env_builder: NeonEnvBuilder):
     Test static endpoint is protected from GC by acquiring and renewing lsn leases.
     """
 
+    LSN_LEASE_LENGTH = 8
     neon_env_builder.num_pageservers = 2
     # GC is manual triggered.
     env = neon_env_builder.init_start(
@@ -139,7 +140,7 @@ def test_readonly_node_gc(neon_env_builder: NeonEnvBuilder):
             "image_creation_threshold": "1",
             "image_layer_creation_check_threshold": "0",
             # Short lease length to fit test.
-            "lsn_lease_length": "3s",
+            "lsn_lease_length": f"{LSN_LEASE_LENGTH}s",
         },
         initial_tenant_shard_count=2,
     )
@@ -170,10 +171,14 @@ def generate_updates_on_main(
     with env.endpoints.create_start("main") as ep_main:
         with ep_main.cursor() as cur:
             cur.execute("CREATE TABLE t0(v0 int primary key, v1 text)")
-        lsn = None
+        lsn = Lsn(0)
         for i in range(2):
             lsn = generate_updates_on_main(env, ep_main, i)
 
+        # Round down to the closest LSN on page boundary (unnormalized).
+        XLOG_BLCKSZ = 8192
+        lsn = Lsn((int(lsn) // XLOG_BLCKSZ) * XLOG_BLCKSZ)
+
         with env.endpoints.create_start(
             branch_name="main",
             endpoint_id="static",
@@ -183,7 +188,8 @@ def generate_updates_on_main(
                 cur.execute("SELECT count(*) FROM t0")
                 assert cur.fetchone() == (ROW_COUNT,)
 
-            time.sleep(3)
+            # Wait for static compute to renew lease at least once.
+            time.sleep(LSN_LEASE_LENGTH / 2)
 
             generate_updates_on_main(env, ep_main, i, end=100)
 
@@ -204,8 +210,9 @@ def generate_updates_on_main(
         # Do some update so we can increment latest_gc_cutoff
         generate_updates_on_main(env, ep_main, i, end=100)
 
+    # Wait for the existing lease to expire.
+    time.sleep(LSN_LEASE_LENGTH)
     # Now trigger GC again, layers should be removed.
-    time.sleep(4)
     for shard, ps in tenant_get_shards(env, env.initial_tenant):
         client = ps.http_client()
         gc_result = client.timeline_gc(shard, env.initial_timeline, 0)