perf: direct-write stdout bypass StringWriter/StringBuffer allocation#680
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He-Pin wants to merge 1 commit intodatabricks:masterfrom
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perf: direct-write stdout bypass StringWriter/StringBuffer allocation#680He-Pin wants to merge 1 commit intodatabricks:masterfrom
He-Pin wants to merge 1 commit intodatabricks:masterfrom
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When writing to stdout (no --output-file), render directly through OutputStreamWriter(BufferedOutputStream(stdout, 65536)) instead of accumulating in a StringWriter then calling toString + println. For large outputs this eliminates ~3x output-size of intermediate char[] allocations from StringBuffer doubling growth + toString copy. The mainConfigured() API gains an optional stdout parameter (default null) that preserves backward compatibility — callers not passing stdout get the existing StringWriter behavior. Upstream: b09647c0
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Motivation
The current output path materializes the entire JSON result into a
StringviaStringWriter, then writes it to stdout. For large outputs, this doubles memory usage (JSON in memory + string copy) and adds GC pressure.Key Design Decision
Write directly to stdout via
OutputStreamWriter, bypassing the intermediateStringWriter/StringBufferallocation entirely. The renderer writes characters directly to the output stream.Modification
StringWriterallocation for stdout outputBenchmark Results
JMH (JVM, 3 iterations warmup + 3 measurement)
Analysis
The realistic2 improvement (-18.1%) is very significant because realistic2 produces large JSON output. By writing directly to stdout, we eliminate the ~303KB intermediate string allocation and the subsequent copy. The comparison2 improvement (-22.2%) also benefits from avoiding the string buffer for its output. This is one of the highest-impact PRs for realistic2 with only 27 lines of code.
References
b09647c0Result
All 5 tests pass. All benchmarks strongly positive, especially realistic2. No regressions.