From 58129fad929f31b5d4920992b3c4b2d7660f3930 Mon Sep 17 00:00:00 2001
From: Benny Halevy <bhalevy@scylladb.com>
Date: Sun, 16 Apr 2023 14:05:57 +0300
Subject: [PATCH] locator/topology: call seastar::current_backtrace only when
 log_level is enabled

`seastar::current_backtrace()` can be quite heavey.
When we pass it to a log message in relatively detailed log_level
(debug/trace), we pay the price of `current_backtrace` every time,
but we rarely print the message.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
---
 locator/topology.cc | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/locator/topology.cc b/locator/topology.cc
index 2efddd6f23..e049012796 100644
--- a/locator/topology.cc
+++ b/locator/topology.cc
@@ -159,7 +159,9 @@ const node* topology::add_node(node_holder nptr) {
     nptr->set_idx(_nodes.size());
     _nodes.emplace_back(std::move(nptr));
 
-    tlogger.debug("topology[{}]: add_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    if (tlogger.is_enabled(log_level::debug)) {
+        tlogger.debug("topology[{}]: add_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    }
 
     try {
         index_node(node);
@@ -171,13 +173,15 @@ const node* topology::add_node(node_holder nptr) {
 }
 
 const node* topology::update_node(node* node, std::optional<host_id> opt_id, std::optional<inet_address> opt_ep, std::optional<endpoint_dc_rack> opt_dr, std::optional<node::state> opt_st) {
-    tlogger.debug("topology[{}]: update_node: {}: to: host_id={} endpoint={} dc={} rack={} state={}, at {}", fmt::ptr(this), debug_format(node),
+    if (tlogger.is_enabled(log_level::debug)) {
+        tlogger.debug("topology[{}]: update_node: {}: to: host_id={} endpoint={} dc={} rack={} state={}, at {}", fmt::ptr(this), debug_format(node),
             opt_id ? format("{}", *opt_id) : "unchanged",
             opt_ep ? format("{}", *opt_ep) : "unchanged",
             opt_dr ? format("{}", opt_dr->dc) : "unchanged",
             opt_dr ? format("{}", opt_dr->rack) : "unchanged",
             opt_st ? format("{}", *opt_st) : "unchanged",
             current_backtrace());
+    }
 
     bool changed = false;
     if (opt_id) {
@@ -270,7 +274,9 @@ void topology::remove_node(const node* node) {
 }
 
 void topology::index_node(const node* node) {
-    tlogger.trace("topology[{}]: index_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    if (tlogger.is_enabled(log_level::trace)) {
+        tlogger.trace("topology[{}]: index_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    }
 
     if (node->idx() < 0) {
         on_internal_error(tlogger, format("topology[{}]: {}: must already have a valid idx", fmt::ptr(this), debug_format(node)));
@@ -314,7 +320,9 @@ void topology::index_node(const node* node) {
 }
 
 void topology::unindex_node(const node* node) {
-    tlogger.trace("topology[{}]: unindex_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    if (tlogger.is_enabled(log_level::trace)) {
+        tlogger.trace("topology[{}]: unindex_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    }
 
     const auto& dc = node->dc_rack().dc;
     const auto& rack = node->dc_rack().rack;
@@ -359,7 +367,9 @@ void topology::unindex_node(const node* node) {
 }
 
 node_holder topology::pop_node(const node* node) {
-    tlogger.trace("topology[{}]: pop_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    if (tlogger.is_enabled(log_level::trace)) {
+        tlogger.trace("topology[{}]: pop_node: {}, at {}", fmt::ptr(this), debug_format(node), current_backtrace());
+    }
 
     unindex_node(node);
 
@@ -410,9 +420,11 @@ const node* topology::find_node(node::idx_type idx) const noexcept {
 
 const node* topology::add_or_update_endpoint(inet_address ep, std::optional<host_id> opt_id, std::optional<endpoint_dc_rack> opt_dr, std::optional<node::state> opt_st)
 {
-    tlogger.trace("topology[{}]: add_or_update_endpoint: ep={} host_id={} dc={} rack={} state={}, at {}", fmt::ptr(this),
+    if (tlogger.is_enabled(log_level::trace)) {
+        tlogger.trace("topology[{}]: add_or_update_endpoint: ep={} host_id={} dc={} rack={} state={}, at {}", fmt::ptr(this),
             ep, opt_id.value_or(host_id::create_null_id()), opt_dr.value_or(endpoint_dc_rack{}).dc, opt_dr.value_or(endpoint_dc_rack{}).rack, opt_st.value_or(node::state::none),
             current_backtrace());
+    }
     auto n = find_node(ep);
     if (n) {
         return update_node(make_mutable(n), opt_id, std::nullopt, std::move(opt_dr), std::move(opt_st));