[ISSUE #10522] Reduce Remoting header encoding allocation via FastCodesHeader/RocketMQSerializable optimizations

[wang-jiahua]

Which Issue(s) This PR Fixes

Fixes #10522

Brief Description

Enhance FastCodesHeader interface and RocketMQSerializable utility to reduce allocation and CPU overhead in the Remoting header encoding/decoding hot path.

FastCodesHeader.java

• Optimize writeIfNotNull to route Long/Integer values through writeDecimalLong/writeDecimalInt instead of value.toString() + writeStr, eliminating transient String allocation.
• Add writeLong(ByteBuf, String, long) and writeInt(ByteBuf, String, int) helper methods for direct primitive encoding.

RocketMQSerializable.java

• Add writeDecimalLong(ByteBuf, long) and writeDecimalInt(ByteBuf, int) — write decimal numbers directly to ByteBuf without String.valueOf() allocation.
• Add SINGLE_BYTE_STRINGS cache (128 entries) — readStr returns cached String for single-byte ASCII values instead of creating new String via readCharSequence.
• Right-size mapDeserialize initial HashMap capacity from 128 to 24 — typical headers have 5-15 entries, 128 causes unnecessary memory waste.

All changes are additive — no existing method signatures are modified.

How Did You Test This Change?

1. Unit tests

mvn test -pl remoting -Dtest=RocketMQSerializableTest,FastCodesHeaderTest
Tests run: 5, Failures: 0, Errors: 0, Skipped: 0

2. A/B benchmark (256 threads, 1KB sync send, Dragonwell JDK 21, 6g heap)

Metric	Baseline (develop)	Optimized (R1)	Change
TPS	~196k	~236k	+20.6%
p99 RT	3ms	2ms	-33%
Average RT	1.307ms	1.085ms	-17.0%
Max RT	594ms	351ms	-40.9%
Young GCs (total)	336	304	-9.5%

3. Commercial compatibility

• Pure additive changes — no existing API signatures modified.
• No commercial classes implement FastCodesHeader.
• Commercial YitianRemotingCommand calls RocketMQSerializable.rocketMQProtocolDecode/Encode which are unchanged.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR optimizes remoting header serialization/deserialization by adding fast-path encoding for numeric values and single-byte strings, and tweaks map allocation to reduce overhead.

Changes:

• Add decimal (ASCII) serialization helpers for int/long values written into a ByteBuf.
• Add a cached fast-path for reading 1-byte UTF-8 strings (ASCII) to avoid allocations/decoding overhead.
• Update header encoding to use the new decimal writers for Long/Integer values and adjust HashMap initial capacity.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
remoting/src/main/java/org/apache/rocketmq/remoting/protocol/RocketMQSerializable.java	Adds decimal numeric writers, single-byte string cache/fast-path, and updates deserialization map pre-sizing.
remoting/src/main/java/org/apache/rocketmq/remoting/protocol/FastCodesHeader.java	Uses new decimal writers for Long/Integer fields and introduces typed writeLong/writeInt helpers.

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[RockteMQ-AI]

Review by github-manager-bot

Summary

This PR optimizes the Remoting header encoding/decoding hot path by eliminating transient String allocations for numeric values and adding a single-byte ASCII string cache. The changes are purely additive with impressive benchmark results (+20.6% TPS, -33% p99 RT).

Findings

• [Positive] FastCodesHeader.java:41-47 — Routing Long/Integer through writeDecimalLong/writeDecimalInt instead of value.toString() + writeStr is a clean and effective allocation elimination. The instanceof branching cost is negligible compared to the allocation savings on the hot path.

• [Positive] RocketMQSerializable.java writeDecimalLong/writeDecimalInt — The Long.MIN_VALUE / Integer.MIN_VALUE edge cases are correctly handled by dividing by 10 first and appending the last digit, avoiding the overflow that -value would cause. Well done.

• [Positive] SINGLE_BYTE_STRINGS cache — 128-entry ASCII cache is a good trade-off: ~5-6KB static memory vs. avoiding new String() for the most common single-byte header values. The readStr fast path (len == 1 && b >= 0) is correct for UTF-8 single-byte range.

• [Positive] mapDeserialize capacity 128 → 24 — Good observation. Typical headers have 5-15 entries; 128 was wasteful. With load factor 0.75, capacity 24 supports 18 entries before resize, which covers the common case.

• [Info] FastCodesHeader.java:41 — Consider reordering the instanceof checks to test String first (most common header value type), then Long, then Integer. This avoids two unnecessary type checks for the majority of calls. Minor optimization, non-blocking.

if (value instanceof String) {
    RocketMQSerializable.writeStr(out, false, (String) value);
} else if (value instanceof Long) {
    RocketMQSerializable.writeDecimalLong(out, (Long) value);
} else if (value instanceof Integer) {
    RocketMQSerializable.writeDecimalInt(out, (Integer) value);
} else {
    RocketMQSerializable.writeStr(out, false, value.toString());
}

• [Info] writePositiveDigits uses a two-pass approach (count digits, then write). An alternative is a pre-allocated digit lookup table indexed by value, but the current approach is clean and the performance difference is negligible for numbers up to 19 digits.

Compatibility

• All changes are additive — no existing method signatures modified.
• New default methods in FastCodesHeader interface do not break existing implementations.
• SINGLE_BYTE_STRINGS is a private static field with no external visibility.
• Wire format is unchanged: writeDecimalLong/writeDecimalInt produce the same byte output as writeStr(out, false, String.valueOf(value)).

Tests

• Unit tests cover RocketMQSerializable and FastCodesHeader directly.
• Benchmark data is well-documented with clear before/after comparison.
• Consider adding an edge-case test for writeDecimalLong(Long.MIN_VALUE) and writeDecimalInt(Integer.MIN_VALUE) to prevent regression of the overflow handling.

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Automated review by github-manager-bot

[codecov-commenter]

Codecov Report

❌ Patch coverage is 7.35294% with 63 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.07%. Comparing base (59a70d9) to head (9a009d9).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
...cketmq/remoting/protocol/RocketMQSerializable.java	8.77%	51 Missing and 1 partial ⚠️
...he/rocketmq/remoting/protocol/FastCodesHeader.java	0.00%	11 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10524      +/-   ##
=============================================
- Coverage      48.19%   48.07%   -0.12%     
+ Complexity     13394    13376      -18     
=============================================
  Files           1377     1377              
  Lines         100730   100801      +71     
  Branches       13012    13029      +17     
=============================================
- Hits           48542    48459      -83     
- Misses         46254    46400     +146     
- Partials        5934     5942       +8     

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