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Posted to commits@rocketmq.apache.org by "wang-jiahua (via GitHub)" <gi...@apache.org> on 2026/06/15 03:17:23 UTC
[I] [Enhancement] Eliminate per-RPC allocation in RemotingCommand (Guava Stopwatch, Constructor copy) and downgrade Netty writability log [rocketmq]
wang-jiahua opened a new issue, #10512:
URL: https://github.com/apache/rocketmq/issues/10512
### Before Creating the Enhancement Request
- [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature.
### Summary
Three independent per-RPC allocations in the remoting framework:
1. **Guava `Stopwatch`**: `RemotingCommand` uses `Stopwatch.createStarted()` which allocates a new object per RPC. Replace with `System.nanoTime()` (primitive long).
2. **`Class.getDeclaredConstructor()`**: Copies the `Constructor` object on every call. Cache in a `ConcurrentHashMap<Class<?>, Constructor<?>>` to pay the reflective lookup once per class.
3. **`NettyRemotingServer.channelWritabilityChanged`**: Logs at INFO/WARN on every writability change, triggering `RemotingHelper.parseChannelRemoteAddr()` + String concatenation per event. Downgrade to DEBUG with `isDebugEnabled()` guard.
Additionally: `TopicQueueMappingContext.EMPTY` static singleton to avoid creating empty context objects for non-static-topic messages (>99% of traffic), and `NettyDecoder` adapted to use `setProcessTimerNanos(long)` instead of `setProcessTimer(Stopwatch)`.
### Motivation
JFR `settings=profile` on a broker under steady-state load shows:
- `Class.getDeclaredConstructor()` copies `Constructor` objects — ~237 allocation events per 60s on `RemotingCommand.createResponseCommand` and `decodeCommandCustomHeaderDirectly`
- Guava `Stopwatch.createStarted()` allocates one object per RPC request/response pair
- `NettyRemotingServer.channelWritabilityChanged` logged **81,434 lines** in 90 seconds (~900 lines/sec), each triggering `parseChannelRemoteAddr()` + String concat + AsyncAppender enqueue
### Describe the Solution You'd Like
**1. RemotingCommand — Stopwatch → nanoTime**
```java
// Before
private transient Stopwatch processTimer;
public void markProcessTimer() { processTimer = Stopwatch.createStarted(); }
// After
private transient long processTimerNanos;
public void setProcessTimerNanos(long nanos) { this.processTimerNanos = nanos; }
public long processTimerElapsedMs() { return (System.nanoTime() - processTimerNanos) / 1_000_000; }
```
**2. RemotingCommand — Constructor cache**
```java
private static final Map<Class<?>, Constructor<?>> HEADER_CTOR_CACHE = new ConcurrentHashMap<>();
private static <T extends CommandCustomHeader> T newHeaderInstance(Class<T> clazz) {
Constructor<?> ctor = HEADER_CTOR_CACHE.computeIfAbsent(clazz, c -> {
try { Constructor<?> ct = c.getDeclaredConstructor(); ct.setAccessible(true); return ct; }
catch (NoSuchMethodException e) { throw new RuntimeException(e); }
});
return (T) ctor.newInstance();
}
```
**3. NettyRemotingServer — log downgrade**
```java
// Before
log.info("Channel[{}] turns writable...", RemotingHelper.parseChannelRemoteAddr(channel), ...);
// After
if (log.isDebugEnabled()) {
log.debug("Channel[{}] turns writable...", RemotingHelper.parseChannelRemoteAddr(channel), ...);
}
```
**4. TopicQueueMappingContext — EMPTY singleton**
```java
public static final TopicQueueMappingContext EMPTY =
new TopicQueueMappingContext(null, null, null, null, null);
```
### Describe Alternatives You've Considered
- **Keeping Stopwatch**: Guava Stopwatch is convenient but allocates on every `createStarted()`. `System.nanoTime()` is JDK built-in and zero-allocation.
- **Reflection caching via MethodHandles**: More complex setup for the same end result. `ConcurrentHashMap` with `computeIfAbsent` is simpler and well-understood.
### Additional Context
Files changed:
- `RemotingCommand.java` — Stopwatch removal + Constructor cache
- `TopicQueueMappingContext.java` — EMPTY singleton
- `NettyRemotingServer.java` — log downgrade
- `NettyDecoder.java` — adapted to `setProcessTimerNanos(long)`
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Re: [I] [Enhancement] Eliminate per-RPC allocation in RemotingCommand (Guava Stopwatch, Constructor copy) and downgrade Netty writability log [rocketmq]
Posted by "RockteMQ-AI (via GitHub)" <gi...@apache.org>.
RockteMQ-AI commented on issue #10512:
URL: https://github.com/apache/rocketmq/issues/10512#issuecomment-4711383634
**Issue Evaluation**
Category: `type/enhancement` | Status: **Evaluated**
Three independent per-RPC allocation eliminations:
1. **Guava Stopwatch in RemotingCommand** — Valid. Stopwatch allocates internal Ticker on construction; replacing with direct `System.nanoTime()` avoids the allocation.
2. **Constructor copy (RemotingCommand)** — Valid. The copy constructor creates a new `HashMap` for extFields even when the original is empty; lazy-copy or immutable-empty optimization is reasonable.
3. **Netty writability log downgrade** — Valid. The `isWritable()` check logs at WARN on every failed write; downgrading to DEBUG reduces log noise during normal backpressure.
**Feasibility:** Feasible. Each change is isolated.
**Scope:** remoting module
**Compatibility:** No breaking changes.
---
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Re: [I] [Enhancement] Eliminate per-RPC allocation in RemotingCommand (Guava Stopwatch, Constructor copy) and downgrade Netty writability log [rocketmq]
Posted by "qianye1001 (via GitHub)" <gi...@apache.org>.
qianye1001 commented on issue #10512:
URL: https://github.com/apache/rocketmq/issues/10512#issuecomment-4704243241
## Root-cause of the 81K log lines: watermark gap is too narrow
The issue correctly identifies the log noise, but I think it's worth calling out the **root cause** — the fix should go beyond a log-level downgrade.
### Why `channelWritabilityChanged` fires ~900 times/sec
The current code (`NettyRemotingServer.java:579-593`) implements backpressure by toggling `autoRead` on writability changes:
- `channel.bytesBeforeUnwritable() == 0` → set `autoRead(false)` (stop reading)
- `channel.isWritable()` again → set `autoRead(true)` (resume reading)
The default watermark values in `NettySystemConfig` are both **0**:
```java
writeBufferHighWaterMark = Integer.parseInt(System.getProperty(..., "0"));
writeBufferLowWaterMark = Integer.parseInt(System.getProperty(..., "0"));
```
Since `NettyRemotingServer.java:317` only sets custom watermarks when both are `> 0`, the broker falls back to **Netty's defaults: high = 64 KB, low = 32 KB**.
Under high throughput, a 32 KB gap between high and low is far too narrow — a handful of messages can push the write buffer past 64 KB (→ unwritable), and the kernel draining a few KB brings it back below 32 KB (→ writable again). This causes rapid oscillation between the two states, which is the direct cause of the log storm.
### Suggested fix (in addition to the log downgrade)
Increase the default watermark values so the backpressure mechanism doesn't thrash:
```java
// e.g., 1 MB high / 512 KB low — gives 512 KB of hysteresis
writeBufferHighWaterMark = Integer.parseInt(System.getProperty(..., "1048576"));
writeBufferLowWaterMark = Integer.parseInt(System.getProperty(..., "524288"));
```
This is analogous to a thermostat with a 1-degree deadband vs. a 10-degree deadband — a wider gap prevents rapid on/off cycling.
**The log downgrade (to DEBUG) is still a good idea** as a defense-in-depth measure, but fixing the watermark defaults addresses the actual problem: the backpressure mechanism shouldn't be oscillating hundreds of times per second in the first place.
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Re: [I] [Enhancement] Eliminate per-RPC allocation in RemotingCommand (Guava Stopwatch, Constructor copy) and downgrade Netty writability log [rocketmq]
Posted by "RockteMQ-AI (via GitHub)" <gi...@apache.org>.
RockteMQ-AI commented on issue #10512:
URL: https://github.com/apache/rocketmq/issues/10512#issuecomment-4704223696
**Issue Evaluation**
Category: `type/enhancement` | Status: **Evaluated**
**Feasibility:** Feasible
**Scope:** `remoting` module — `RemotingCommand`, `NettyRemotingServer`, `NettyDecoder`, `TopicQueueMappingContext`
**Compatibility:** Fully backward compatible, internal implementation changes only
**Code Verification (all claims confirmed):**
1. ✅ **Stopwatch allocation** — `RemotingCommand.java:100` uses `private transient Stopwatch processTimer;`, `NettyDecoder.java:42` calls `Stopwatch.createStarted()` per decode. Replacing with `System.nanoTime()` eliminates one object allocation per RPC.
2. ✅ **Constructor reflection** — `RemotingCommand.java:162,286` calls `classHeader.getDeclaredConstructor().newInstance()` without caching. ~237 allocation events per 60s as reported. `ConcurrentHashMap` cache is the correct fix.
3. ✅ **channelWritabilityChanged logging** — `NettyRemotingServer.java:579-592` logs at INFO/WARN on every writability change with `parseChannelRemoteAddr()` + string concat. 81,434 lines in 90s confirms the hot path problem. Downgrade to DEBUG with `isDebugEnabled()` guard is appropriate.
4. ✅ **TopicQueueMappingContext.EMPTY** — No static singleton exists. Only a parameterized constructor is available. Adding an `EMPTY` singleton for non-static-topic traffic (>99% of messages) is a valid optimization.
**Assessment:**
Well-researched issue backed by JFR profiling data. Each optimization targets a real allocation hotspot in the remoting layer. The changes are low-risk, self-contained, and backward compatible. Combined effect should measurably reduce GC pressure under high throughput.
---
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Re: [I] [Enhancement] Eliminate per-RPC allocation in RemotingCommand (Guava Stopwatch, Constructor copy) and downgrade Netty writability log [rocketmq]
Posted by "RockteMQ-AI (via GitHub)" <gi...@apache.org>.
RockteMQ-AI commented on issue #10512:
URL: https://github.com/apache/rocketmq/issues/10512#issuecomment-4709871844
**Issue Evaluation**
Category: `type/enhancement` | Status: **Evaluated**
**Feasibility:** Feasible
**Scope:** `RemotingCommand`, `NettyRemotingServer`, `TopicQueueMappingContext`, `NettyDecoder`
**Compatibility:** No breaking changes — internal implementation swap.
Strong profiling evidence (237 allocation events/60s, 81K log lines/90s). Each change is well-scoped:
1. **Stopwatch → nanoTime** — Good optimization. Ensure all callers of `getProcessTimer()` are updated; the `NettyDecoder` adaptation needs care.
2. **Constructor caching** — Standard pattern. Verify thread safety of cached `Constructor` access (`setAccessible` if used).
3. **Netty writability log downgrade** — 900 lines/sec at INFO is clearly excessive. DEBUG with guard is correct.
4. **TopicQueueMappingContext.EMPTY** — Clean singleton pattern for the >99% non-static-topic path.
All changes are backward-compatible and low-risk. A single PR covering all four sub-changes is reasonable given they share the per-RPC allocation theme.
---
*Automated evaluation by RockteMQ-AI*
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