From eafae92795397939f31b933168f0328a1cfcdde2 Mon Sep 17 00:00:00 2001
From: Vlad Lazar <vlad@neon.tech>
Date: Thu, 10 Oct 2024 20:30:17 +0200
Subject: [PATCH] pageserver: make io serial by default

One can configure this via the NEON_PAGESERVER_VALUE_RECONSTRUCT_IO_CONCURRENCY
env var. A config is possible as well, but it's more work and this is
enough for experimentation.
---
 pageserver/src/tenant/storage_layer.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pageserver/src/tenant/storage_layer.rs b/pageserver/src/tenant/storage_layer.rs
index 4254664bf7..e4433fc2a5 100644
--- a/pageserver/src/tenant/storage_layer.rs
+++ b/pageserver/src/tenant/storage_layer.rs
@@ -195,7 +195,8 @@ impl ValuesReconstructState {
             io_concurrency: {
                 static IO_CONCURRENCY: once_cell::sync::Lazy<String> =
                     once_cell::sync::Lazy::new(|| {
-                        std::env::var("NEON_PAGESERVER_VALUE_RECONSTRUCT_IO_CONCURRENCY").unwrap()
+                        std::env::var("NEON_PAGESERVER_VALUE_RECONSTRUCT_IO_CONCURRENCY")
+                            .unwrap_or_else(|_| "serial".to_string())
                     });
                 match IO_CONCURRENCY.as_str() {
                     "parallel" => IoConcurrency::Parallel,