Fix test_ts_of_lsn_api flakiness (#7599)

Changes parameters to fix the flakiness of `test_ts_of_lsn_api`. Already
now, the amount of flakiness of the test is pretty low. With this, it's
even lower.

cc #5768

test_runner/fixtures/pageserver/allowed_errors.py

@@ -89,6 +89,8 @@ DEFAULT_PAGESERVER_ALLOWED_ERRORS = (
     # During teardown, we stop the storage controller before the pageservers, so pageservers
     # can experience connection errors doing background deletion queue work.
     ".*WARN deletion backend: calling control plane generation validation API failed.*Connection refused.*",
+    # Can happen when the test shuts down the storage controller while it is calling the utilization API
+    ".*WARN.*path=/v1/utilization .*request was dropped before completing",
 )
 
 

test_runner/regress/test_lsn_mapping.py

@@ -119,11 +119,11 @@ def test_ts_of_lsn_api(neon_env_builder: NeonEnvBuilder):
 
     cur = endpoint_main.connect().cursor()
     # Create table, and insert rows, each in a separate transaction
-    # Disable synchronous_commit to make this initialization go faster.
+    # Enable synchronous commit as we are timing sensitive
     #
     # Each row contains current insert LSN and the current timestamp, when
     # the row was inserted.
-    cur.execute("SET synchronous_commit=off")
+    cur.execute("SET synchronous_commit=on")
     cur.execute("CREATE TABLE foo (x integer)")
     tbl = []
     for i in range(1000):
@@ -132,7 +132,7 @@ def test_ts_of_lsn_api(neon_env_builder: NeonEnvBuilder):
         after_timestamp = query_scalar(cur, "SELECT clock_timestamp()").replace(tzinfo=timezone.utc)
         after_lsn = query_scalar(cur, "SELECT pg_current_wal_lsn()")
         tbl.append([i, after_timestamp, after_lsn])
-        time.sleep(0.005)
+        time.sleep(0.02)
 
     # Execute one more transaction with synchronous_commit enabled, to flush
     # all the previous transactions