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Resolve backend DNS on a bounded thread pool to avoid head-of-line blocking #1834

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Merged
WouterGritter merged 2 commits into from
Jul 8, 2026
+12 −5
Merged

Resolve backend DNS on a bounded thread pool to avoid head-of-line blocking #1834

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f67ebac
Use a bounded thread pool for backend DNS resolution
carlodrift Jun 28, 2026
5aa2a3f
Queue DNS lookups instead of rejecting when the resolver pool is busy
carlodrift Jul 7, 2026
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17 changes: 12 additions & 5 deletions ...y/src/main/java/com/velocitypowered/proxy/network/netty/SeparatePoolInetNameResolver.java
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Original file line number Diff line number Diff line change
Expand Up @@ -32,17 +32,20 @@
import java.net.InetSocketAddress;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
* An implementation of {@code InetNameResolver} that performs blocking DNS name lookups
* in a separate thread, avoiding blocking the Netty threads for an extended period of time
* and without the downsides of Netty's native DNS resolver.
* on a small bounded pool of separate threads, avoiding blocking the Netty threads for an
* extended period of time and without the downsides of Netty's native DNS resolver.
*/
public final class SeparatePoolInetNameResolver extends InetNameResolver {

private static final int MAX_RESOLVE_THREADS = 8;

private final ExecutorService resolveExecutor;
private final InetNameResolver delegate;
private final Cache<String, List<InetAddress>> cache;
Expand All @@ -56,11 +59,15 @@ public final class SeparatePoolInetNameResolver extends InetNameResolver {
*/
public SeparatePoolInetNameResolver(EventExecutor executor) {
super(executor);
this.resolveExecutor = Executors.newSingleThreadExecutor(
ThreadPoolExecutor resolveExecutor = new ThreadPoolExecutor(
MAX_RESOLVE_THREADS, MAX_RESOLVE_THREADS,
60L, TimeUnit.SECONDS, new LinkedBlockingQueue<>(),
new ThreadFactoryBuilder()
.setNameFormat("Velocity DNS Resolver")
.setNameFormat("Velocity DNS Resolver #%d")
.setDaemon(true)
.build());
resolveExecutor.allowCoreThreadTimeOut(true);
this.resolveExecutor = resolveExecutor;
this.delegate = new DefaultNameResolver(executor);
this.cache = Caffeine.newBuilder()
.expireAfterWrite(30, TimeUnit.SECONDS)
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