From 4b459c6855f10bc4559d24ba927347e6ef034d34 Mon Sep 17 00:00:00 2001
From: Pawel Pery <pawel.pery@scylladb.com>
Date: Thu, 7 Aug 2025 16:22:46 +0200
Subject: [PATCH 1/2] vector_store_client: disable Nagle's algorithm on the
 http client
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Nagle’s algorithm and Delayed ACK’s algorithm are enabled by default on sockets
in Linux. As a result we can experience 40ms latency on simply waiting for ACK
on the client side. Disabling the Nagle’s algorithm (using TCP_NODELAY) should
fix the issue (client won’t wait 40ms for ACKs).

This patch sets `TCP_NODELAY` on every socket created by the `http_client`.
---
 service/vector_store_client.cc | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/service/vector_store_client.cc b/service/vector_store_client.cc
index 8eea20f700..df14478957 100644
--- a/service/vector_store_client.cc
+++ b/service/vector_store_client.cc
@@ -211,6 +211,21 @@ auto read_ann_json(rjson::value const& json, schema_ptr const& schema) -> std::e
     return std::move(keys);
 }
 
+class client_connection_factory : public http::experimental::connection_factory {
+    socket_address _addr;
+
+public:
+    explicit client_connection_factory(socket_address addr)
+        : _addr(addr) {
+    }
+
+    future<connected_socket> make([[maybe_unused]] abort_source* as) override {
+        auto socket = co_await seastar::connect(_addr, {}, transport::TCP);
+        socket.set_nodelay(true);
+        co_return socket;
+    }
+};
+
 class http_client {
 
     host_port _host_port;
@@ -222,7 +237,7 @@ public:
     http_client(host_port host_port_, inet_address addr)
         : _host_port(std::move(host_port_))
         , _addr(std::move(addr))
-        , impl(socket_address(addr, _host_port.port)) {
+        , impl(std::make_unique<client_connection_factory>(socket_address(addr, _host_port.port))) {
     }
 
     bool connects_to(inet_address const& a, port_number p) const {

From 509f5ddb89d93ea6fbf241d35721f9308d1a3ad5 Mon Sep 17 00:00:00 2001
From: Pawel Pery <pawel.pery@scylladb.com>
Date: Thu, 7 Aug 2025 16:53:41 +0200
Subject: [PATCH 2/2] vector_store_client: set keepalive for the http client's
 socket

Checking for dead peers or network is helpful in maintaining a lifetime of the
http client. This patch sets TCP_KEEPALIVE option on the http client's socket.
---
 service/vector_store_client.cc | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/service/vector_store_client.cc b/service/vector_store_client.cc
index df14478957..f8a85b0572 100644
--- a/service/vector_store_client.cc
+++ b/service/vector_store_client.cc
@@ -31,6 +31,8 @@
 
 namespace {
 
+using namespace std::chrono_literals;
+
 using ann_error = service::vector_store_client::ann_error;
 using configuration_exception = exceptions::configuration_exception;
 using duration = lowres_clock::duration;
@@ -46,6 +48,7 @@ using port_number = service::vector_store_client::port_number;
 using primary_key = service::vector_store_client::primary_key;
 using primary_keys = service::vector_store_client::primary_keys;
 using service_reply_format_error = service::vector_store_client::service_reply_format_error;
+using tcp_keepalive_params = net::tcp_keepalive_params;
 using time_point = lowres_clock::time_point;
 
 // Wait time before retrying after an exception occurred
@@ -222,6 +225,12 @@ public:
     future<connected_socket> make([[maybe_unused]] abort_source* as) override {
         auto socket = co_await seastar::connect(_addr, {}, transport::TCP);
         socket.set_nodelay(true);
+        socket.set_keepalive_parameters(tcp_keepalive_params{
+                .idle = 60s,
+                .interval = 60s,
+                .count = 10,
+        });
+        socket.set_keepalive(true);
         co_return socket;
     }
 };