pageserver: remove trace_read_requests (#8338)

`trace_read_requests` is a per `Tenant`-object option.
But the `handle_pagerequests` loop doesn't know which
`Tenant` object (i.e., which shard) the request is for.

The remaining use of the `Tenant` object is to check `tenant.cancel`.
That check is incorrect [if the pageserver hosts multiple
shards](https://github.com/neondatabase/neon/issues/7427#issuecomment-2220577518).
I'll fix that in a future PR where I completely eliminate the holding
of `Tenant/Timeline` objects across requests.
See [my code RFC](https://github.com/neondatabase/neon/pull/8286) for
the
high level idea.

Note that we can always bring the tracing functionality if we need it.
But since it's actually about logging the `page_service` wire bytes,
it should be a `page_service`-level config option, not per-Tenant.
And for enabling tracing on a single connection, we can implement
a `set pageserver_trace_connection;` option.

test_runner/fixtures/compare_fixtures.py

@@ -109,8 +109,6 @@ class NeonCompare(PgCompare):
 
         # Create tenant
         tenant_conf: Dict[str, str] = {}
-        if False:  # TODO add pytest setting for this
-            tenant_conf["trace_read_requests"] = "true"
         self.tenant, _ = self.env.neon_cli.create_tenant(conf=tenant_conf)
 
         # Create timeline

test_runner/regress/test_attach_tenant_config.py

@@ -168,7 +168,6 @@ def test_fully_custom_config(positive_env: NeonEnv):
             "refill_amount": 1000,
             "max": 1000,
         },
-        "trace_read_requests": True,
         "walreceiver_connect_timeout": "13m",
         "image_layer_creation_check_threshold": 1,
         "switch_aux_file_policy": "cross-validation",

test_runner/regress/test_read_trace.py

@@ -1,39 +0,0 @@
-from contextlib import closing
-
-from fixtures.common_types import Lsn
-from fixtures.neon_fixtures import NeonEnvBuilder
-from fixtures.pageserver.utils import wait_for_last_record_lsn
-from fixtures.utils import query_scalar
-
-
-# This test demonstrates how to collect a read trace. It's useful until
-# it gets replaced by a test that actually does stuff with the trace.
-#
-# Additionally, tests that pageserver is able to create tenants with custom configs.
-def test_read_request_tracing(neon_env_builder: NeonEnvBuilder):
-    neon_env_builder.num_safekeepers = 1
-    env = neon_env_builder.init_start(
-        initial_tenant_conf={
-            "trace_read_requests": "true",
-        }
-    )
-
-    tenant_id = env.initial_tenant
-    timeline_id = env.initial_timeline
-    endpoint = env.endpoints.create_start("main")
-
-    with closing(endpoint.connect()) as conn:
-        with conn.cursor() as cur:
-            cur.execute("create table t (i integer);")
-            cur.execute(f"insert into t values (generate_series(1,{10000}));")
-            cur.execute("select count(*) from t;")
-            current_lsn = Lsn(query_scalar(cur, "SELECT pg_current_wal_flush_lsn()"))
-    # wait until pageserver receives that data
-    pageserver_http = env.pageserver.http_client()
-    wait_for_last_record_lsn(pageserver_http, tenant_id, timeline_id, current_lsn)
-
-    # Stop postgres so we drop the connection and flush the traces
-    endpoint.stop()
-
-    trace_path = env.pageserver.workdir / "traces" / str(tenant_id) / str(timeline_id)
-    assert trace_path.exists()