From 0dfd92d0b34c8765859863c285df04a02aa1054d Mon Sep 17 00:00:00 2001
From: Benny Halevy <bhalevy@scylladb.com>
Date: Fri, 29 Jul 2022 18:27:13 +0300
Subject: [PATCH] token_metadata: allow update_normal_token_owners to yield

Given #11146, we see a 10ms stall when calculate_natural_endpoints
calls get_all_endpoints that up until this patch performed a
similar loop on the `_token_to_endpoint_map`, so to prevent such
a stall with large number of tokens, turn update_normal_token_owners
async, and allow yielding in the per-token tight loop.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
---
 locator/token_metadata.cc | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/locator/token_metadata.cc b/locator/token_metadata.cc
index 0b0eee558e..3275053a55 100644
--- a/locator/token_metadata.cc
+++ b/locator/token_metadata.cc
@@ -279,7 +279,7 @@ public:
      * Bootstrapping tokens are not taken into account. */
     size_t count_normal_token_owners() const;
 private:
-    void update_normal_token_owners();
+    future<> update_normal_token_owners();
 
 public:
     // returns empty vector if keyspace_name not found.
@@ -481,7 +481,7 @@ future<> token_metadata_impl::update_normal_tokens(const std::unordered_map<inet
             }
         }
     }
-    update_normal_token_owners();
+    co_await update_normal_token_owners();
 
     // New tokens were added to _token_to_endpoint_map
     // so re-sort all tokens.
@@ -915,10 +915,11 @@ size_t token_metadata_impl::count_normal_token_owners() const {
     return _normal_token_owners.size();
 }
 
-void token_metadata_impl::update_normal_token_owners() {
+future<> token_metadata_impl::update_normal_token_owners() {
     std::unordered_set<inet_address> eps;
     for (auto [t, ep]: _token_to_endpoint_map) {
         eps.insert(ep);
+        co_await coroutine::maybe_yield();
     }
     _normal_token_owners = std::move(eps);
 }