From 291290db92f2720a298390c229bea81f3b56e3e9 Mon Sep 17 00:00:00 2001
From: Charles Hall <charles@computer.surgery>
Date: Wed, 26 Jul 2023 13:24:44 -0700
Subject: [PATCH] maximize fd limit

---
 Cargo.lock  | 32 +++++++++++++++++++++++++++++++-
 Cargo.toml  |  3 +++
 src/main.rs | 21 +++++++++++++++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index 3480c014..7ddf4875 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -382,6 +382,7 @@ dependencies = [
  "jsonwebtoken",
  "lazy_static",
  "lru-cache",
+ "nix",
  "num_cpus",
  "opentelemetry",
  "opentelemetry-jaeger",
@@ -533,7 +534,7 @@ dependencies = [
  "autocfg",
  "cfg-if",
  "crossbeam-utils",
- "memoffset",
+ "memoffset 0.9.0",
  "scopeguard",
 ]
 
@@ -1471,6 +1472,15 @@ version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
 
+[[package]]
+name = "memoffset"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5de893c32cde5f383baa4c04c5d6dbdd735cfd4a794b0debdb2bb1b421da5ff4"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "memoffset"
 version = "0.9.0"
@@ -1513,6 +1523,20 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "nix"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfdda3d196821d6af13126e40375cdf7da646a96114af134d5f417a9a1dc8e1a"
+dependencies = [
+ "bitflags 1.3.2",
+ "cfg-if",
+ "libc",
+ "memoffset 0.7.1",
+ "pin-utils",
+ "static_assertions",
+]
+
 [[package]]
 name = "nom"
 version = "7.1.3"
@@ -2673,6 +2697,12 @@ dependencies = [
  "der",
 ]
 
+[[package]]
+name = "static_assertions"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
+
 [[package]]
 name = "subslice"
 version = "0.2.3"
diff --git a/Cargo.toml b/Cargo.toml
index 9196cf46..7a157f4c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -104,6 +104,9 @@ async-trait = "0.1.68"
 
 sd-notify = { version = "0.4.1", optional = true }
 
+[target.'cfg(unix)'.dependencies]
+nix = { version = "0.26.2", features = ["resource"] }
+
 [features]
 default = ["conduit_bin", "backend_sqlite", "backend_rocksdb", "systemd"]
 #backend_sled = ["sled"]
diff --git a/src/main.rs b/src/main.rs
index 579eeb15..eb7e833b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -54,6 +54,16 @@ static GLOBAL: Jemalloc = Jemalloc;
 
 #[tokio::main]
 async fn main() {
+    // This is needed for opening lots of file descriptors, which tends to
+    // happen more often when using RocksDB and making lots of federation
+    // connections at startup. The soft limit is usually 1024, and the hard
+    // limit is usually 512000; I've personally seen it hit >2000.
+    //
+    // * https://www.freedesktop.org/software/systemd/man/systemd.exec.html#id-1.12.2.1.17.6
+    // * https://github.com/systemd/systemd/commit/0abf94923b4a95a7d89bc526efc84e7ca2b71741
+    #[cfg(unix)]
+    maximize_fd_limit().expect("should be able to increase the soft limit to the hard limit");
+
     // Initialize DB
     let raw_config =
         Figment::new()
@@ -550,3 +560,14 @@ fn method_to_filter(method: Method) -> MethodFilter {
         m => panic!("Unsupported HTTP method: {m:?}"),
     }
 }
+
+#[cfg(unix)]
+fn maximize_fd_limit() -> Result<(), nix::errno::Errno> {
+    use nix::sys::resource::{getrlimit, setrlimit, Resource};
+
+    let res = Resource::RLIMIT_NOFILE;
+
+    let (_, hard_limit) = getrlimit(res)?;
+
+    setrlimit(res, hard_limit, hard_limit)
+}