From 6bcfd6441f6b0b12e3fa3b71282c5474780f08ac Mon Sep 17 00:00:00 2001
From: Bojan Serafimov <bojan.serafimov7@gmail.com>
Date: Mon, 12 Sep 2022 10:26:31 -0400
Subject: [PATCH] Add tracer

---
 pageserver/src/layered_repository.rs |  8 ++++++++
 pageserver/src/lib.rs                |  1 +
 pageserver/src/page_service.rs       | 18 +++++++++++++++---
 pageserver/src/trace.rs              | 21 +++++++++++++++++++++
 4 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 pageserver/src/trace.rs

diff --git a/pageserver/src/layered_repository.rs b/pageserver/src/layered_repository.rs
index 200834300b..f53a2365d0 100644
--- a/pageserver/src/layered_repository.rs
+++ b/pageserver/src/layered_repository.rs
@@ -567,6 +567,14 @@ impl Repository {
             .unwrap_or(self.conf.default_tenant_conf.max_lsn_wal_lag)
     }
 
+    // TODO is there a need for all this boilerplate?
+    pub fn get_trace_read_requests(&self) -> bool {
+        let tenant_conf = self.tenant_conf.read().unwrap();
+        tenant_conf
+            .trace_read_requests
+            .unwrap_or(self.conf.default_tenant_conf.trace_read_requests)
+    }
+
     pub fn update_tenant_config(&self, new_tenant_conf: TenantConfOpt) -> Result<()> {
         let mut tenant_conf = self.tenant_conf.write().unwrap();
 
diff --git a/pageserver/src/lib.rs b/pageserver/src/lib.rs
index 4731179e22..91e834be70 100644
--- a/pageserver/src/lib.rs
+++ b/pageserver/src/lib.rs
@@ -17,6 +17,7 @@ pub mod tenant_mgr;
 pub mod tenant_tasks;
 pub mod thread_mgr;
 pub mod timelines;
+pub mod trace;
 pub mod virtual_file;
 pub mod walingest;
 pub mod walreceiver;
diff --git a/pageserver/src/page_service.rs b/pageserver/src/page_service.rs
index c151bacaa3..54a2b4d463 100644
--- a/pageserver/src/page_service.rs
+++ b/pageserver/src/page_service.rs
@@ -38,6 +38,7 @@ use crate::reltag::RelTag;
 use crate::tenant_mgr;
 use crate::thread_mgr;
 use crate::thread_mgr::ThreadKind;
+use crate::trace::Tracer;
 use crate::CheckpointConfig;
 use postgres_ffi::v14::xlog_utils::to_pg_timestamp;
 
@@ -448,6 +449,15 @@ impl PageServerHandler {
         //       so there is no need to reset the association
         thread_mgr::associate_with(Some(tenant_id), Some(timeline_id));
 
+        // Make request tracer if needed
+        let repo = tenant_mgr::get_repository_for_tenant(tenant_id)?;
+        let trace_read_requests = repo.get_trace_read_requests();
+        let tracer = if trace_read_requests {
+            Some(Tracer::new())
+        } else {
+            None
+        };
+
         // Check that the timeline exists
         let timeline = get_local_timeline(tenant_id, timeline_id)?;
 
@@ -472,7 +482,11 @@ impl PageServerHandler {
                         let tenant_id = tenant_id.to_string();
                         let timeline_id = timeline_id.to_string();
 
-                        // TODO(now) append to trace if tenant is configured for read tracing
+                        // Trace request if needed
+                        if let Some(t) = tracer {
+                            t.trace() // TODO(now) pass zenith_fe_msg
+                        }
+
                         let response = match zenith_fe_msg {
                             PagestreamFeMessage::Exists(req) => SMGR_QUERY_TIME
                                 .with_label_values(&["get_rel_exists", &tenant_id, &timeline_id])
@@ -855,8 +869,6 @@ impl postgres_backend::Handler for PageServerHandler {
 
             self.check_permission(Some(tenantid))?;
 
-            // TODO(now) make trace logger if tenant is configured for read tracing.
-            //           Also flush trace logger on drop.
             self.handle_pagerequests(pgb, timelineid, tenantid)?;
         } else if query_string.starts_with("basebackup ") {
             let (_, params_raw) = query_string.split_at("basebackup ".len());
diff --git a/pageserver/src/trace.rs b/pageserver/src/trace.rs
new file mode 100644
index 0000000000..fecef65604
--- /dev/null
+++ b/pageserver/src/trace.rs
@@ -0,0 +1,21 @@
+pub struct Tracer {}
+
+impl Drop for Tracer {
+    fn drop(&mut self) {
+        self.flush()
+    }
+}
+
+impl Tracer {
+    pub fn new() -> Self {
+        Tracer {}
+    }
+
+    pub fn trace(&mut self) {
+        // TODO(now) implement
+    }
+
+    pub fn flush(&mut self) {
+        // TODO(now) implement
+    }
+}