[PR] [improve][client] Avoid eager broker metadata allocation for outgoing messages [pulsar]

["lhotari (via GitHub)" <gi...@apache.org>]

lhotari opened a new pull request, #26521:
URL: https://github.com/apache/pulsar/pull/26521

   ### Motivation
   
   The `MessageImpl` recycler constructor eagerly allocates `BrokerEntryMetadata` for outgoing messages, although those messages do not yet have broker-added timestamp or index information. This creates an unused object whenever a fresh `MessageImpl` is allocated.
   
   ### Modifications
   
   Remove that constructor allocation, leaving the field null until metadata is supplied. Existing timestamp/index accessors already handle null, and incoming deserialization supplies parsed metadata. Add coverage for absent metadata, explicitly assigned timestamp/index values, and absence after recycling followed by message creation. Include a focused outgoing-message construction benchmark.
   
   ### Verifying this change
   
   Prior Linux x86_64 / Corretto 25 / ZGC JMH measurements showed **608 → 552 B per fresh message**, saving **56 B**, and approximately 8.6% less construction time. The benchmark excludes builder allocation, serialization and networking. Both ordinary-worker modes allocate fresh messages even when `recycle()` is called; already-reused instances do not incur this constructor cost. These are historical experiment results, not new measurements of the extracted branch or a throughput claim.
   
   Local extraction validation passed: all required Spotless and main/test Checkstyle checks, 43 message/builder/broker-metadata test cases with zero failures or skips, and benchmark compilation.
   
   ```shell
   ./gradlew spotlessCheck checkstyleMain checkstyleTest \
     :pulsar-client-original:test \
     --tests org.apache.pulsar.client.impl.MessageImplTest \
     --tests org.apache.pulsar.client.impl.TypedMessageBuilderImplTest \
     :pulsar-broker:test \
     --tests org.apache.pulsar.broker.service.BrokerEntryMetadataE2ETest \
     :microbench:compileJava -PtestRetryCount=0 --max-workers=2 --no-parallel
   ```
   
   The lifecycle test does not assume that ordinary test threads retrieve the same pooled instance. Existing broker-metadata end-to-end tests cover parsed metadata behavior.
   
   - [ ] Make sure that the change passes the CI checks.
   
   ### Does this pull request potentially affect one of the following parts:
   
   - [ ] Dependencies (add or upgrade a dependency)
   - [ ] The public API
   - [ ] The schema
   - [ ] The default values of configurations
   - [ ] The threading model
   - [ ] The binary protocol
   - [ ] The REST endpoints
   - [ ] The admin CLI options
   - [ ] The metrics
   - [ ] Anything that affects deployment
   


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Re: [PR] [improve][client] Avoid eager broker metadata allocation for outgoing messages [pulsar]

["merlimat (via GitHub)" <gi...@apache.org>]

merlimat merged PR #26521:
URL: https://github.com/apache/pulsar/pull/26521


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