latency recorder sketches

if we just want to draw a pie chart.rs

@@ -0,0 +1,35 @@
+// If we just want to draw a pie chart of where latency goes,
+// then we can project the `if we want to draw a jaeger trace.rs` into these structures.
+// - fold `Vec<...>` into a sum
+// - fold `start_time` and `end_time` into deltas
+
+struct SmgrLatencyRecorder {
+    parse_request: u64,
+    downstairs: Arc<Mutex<Downstairs>>,
+    flush_response: u64,
+}
+
+struct Downstairs {
+    wait_for_execution: u64, // batching happens here
+    execution: Arc<Mutex<Execution>>,
+}
+
+struct Execution {
+    traverse_and_submit: Plan,
+    wait_for_io_completions_and_walredo: WaitForIoCompletionsAndWalredo,
+}
+
+struct Plan {
+    visit_layer: VisitLayer,
+    // implict remainder: time in the fringe code and traversing timeline ancestor graph
+}
+
+struct VisitLayer {
+    index_lookup: u64,
+    submit_io: u64,
+}
+
+struct WaitForIoCompletionsAndWalredo {
+    wait_for_io_completions: u64,
+    walredo: u64,
+}

if we want to draw a jaeger trace.rs

@@ -0,0 +1,69 @@
+// If we want to draw a Jaeger trace
+
+struct SmgrLatencyRecorder {
+    start_time: Instant,
+    parse_request: ParseRequest,
+    downstairs: Arc<Mutex<Downstairs>>,
+    flush_response: FlushResponse,
+    end_time: Instant,
+}
+
+struct ParseRequest {
+    start_time: Instant,
+    end_time: Instant,
+}
+
+struct FlushResponse {
+    start_time: Instant,
+    end_time: Instant,
+}
+
+struct Downstairs {
+    start_time: Instant,
+    wait_for_execution: WaitForExecution, // batching happens here
+    execution: Arc<Mutex<Execution>>,
+    end_time: Instant,
+}
+
+enum WaitForExecution {
+    start_time: Instant,
+    end_time: Instant,
+}
+
+struct Execution {
+    start_time: Instant,
+    traverse_and_submit: Plan,
+    wait_for_io_completions_and_walredo: Vec<Arc<Mutex<WaitForIoCompletionsAndWalredo>>>,
+    end_time: Instant,
+}
+
+struct Plan {
+    start_time: Instant,
+    visit_layer: Vec<VisitLayer>,
+    // implict remainder: time in the fringe code and traversing timeline ancestor graph
+    end_time: Instant,
+}
+
+struct VisitLayer {
+    start_time: Instant,
+    index_lookup: IndexLookup,
+    submit_io: SubmitIo,
+    end_time: Instant,
+}
+
+struct IndexLookup {
+    start_time: Instant,
+    end_time: Instant,
+}
+
+struct SubmitIo {
+    start_time: Instant,
+    end_time: Instant,
+}
+
+struct WaitForIoCompletionsAndWalredo {
+    start_time: Instant,
+    wait_for_io_completions: u64,
+    walredo: u64,
+    end_time: Instant,
+}