perf: speed up manifest JSON rendering#874
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Motivation: std.manifestJson* still contributed to the local Scala Native gap versus source-built jrsonnet, especially in real-world object-heavy rendering. Modification: Add an internal StringBuilder-backed FastMaterializeJsonRenderer for std.manifestJson, std.manifestJsonMinified, and std.manifestJsonEx while preserving the public MaterializeJsonRenderer StringWriter API. Reuse an in-place codepoint key sorter backed by java.util.Arrays.sort, and fix raw-surrogate prefix ordering in compareStringsByCodepoint. Result: Full validation passed: ./mill --no-server --ticker false --color false __.reformat and ./mill --no-server --ticker false --color false -j 1 __.test reported 451/451 tests passing. JMH regressions: manifestJsonEx 0.055 ms/op, realistic2 43.596 ms/op, gen_big_object 0.842 ms/op. Direct hyperfine against source-built jrsonnet: manifestJsonEx sjsonnet-native 5.090 ms vs jrsonnet 4.075 ms; kube-prometheus sjsonnet-native 143.738 ms vs jrsonnet 97.385 ms.
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Motivation: The JVM/char render hot path (BaseCharRenderer.visitNonNullString) ran a CharSWAR.hasEscapeChar scan on every string, even for Val.AsciiSafeStr which is statically known to need no JSON escaping (chars 0x20-0x7e, no quote/backslash). The Native ByteRenderer already had this bypass; the char path did not. Modification: - Add BaseCharRenderer.visitAsciiSafeString: quote + bulk getChars + quote, correct even under escapeUnicode since all chars are <= 0x7e. - Route Val.AsciiSafeStr through it via a Materializer.visitStr helper at the three value-string sites; ujson.Value AST path falls back to visitString. - Add AsciiSafeRenderBenchmark to isolate the render path for A/B. Result: JMH render-only, 335KB string-heavy output: 1.606 -> 1.441 ms/op (-10.3%, non-overlapping error bands). 450/450 tests pass.
Motivation: std.manifestTomlEx routed through java.io.StringWriter, whose backing StringBuffer pays a monitor enter/exit on every write/flush on the hot TOML manifestation path. The JSON renderer already switched to the unsynchronized StringBuilderWriter in databricks#874 (-9.3% on kube-prometheus native); TOML did not. Modification: - Switch TomlRenderer and the manifestTomlEx render path in ManifestModule from java.io.StringWriter to the package-private StringBuilderWriter. Output is byte-identical. std.deepJoin keeps StringWriter (separate concern). - Add TomlRenderBenchmark to A/B the render path. Result: Native hyperfine, TOML-heavy workload (1.79MB output): after ran 1.11 ± 0.07x faster than before (~10%), output byte-identical. JMH (whole-pipeline) showed AFTER < BEFORE in two independent rounds. 450/450 tests pass.
Motivation: Parser.Pos is invoked for nearly every AST node. It was `Index.map(off => new Position(...))`: fastparse's `Index` stores the offset as an Int in its `successValue: Any` field (boxing it), and the `.map` then unboxes it and allocates a closure — per node. boxToInteger via SharedPackageDefs.Index was a top self-frame in the parse flamegraph on kube-prometheus. Modification: - Rewrite Pos to write the Position object straight into successValue via ctx.freshSuccess(new Position(fileScope, ctx.index)), skipping the Int box/unbox and the map closure. Parse output (positions/errors) is unchanged. Result: JMH ParserBenchmark (parse-only, all test-suite files): 1.669 -> 1.579 ms/op (+5.4%, non-overlapping bands). Native parse_time on kube-prometheus: ~105.6 -> ~100.9 ms (+4.5%, consistent). Output byte-identical. 450/450 tests pass.
Motivation:
exprSuffix2 was `Pos.flatMapX { i => CharIn(".[({")... }`, which allocated a
Position on EVERY attempt — including the failing attempt that terminates
`exprSuffix2.rep` after each expression. Most subexpressions have no suffix, so
that trailing failed attempt (one per expression) allocated a Position that was
immediately discarded.
Modification:
- Match the suffix char first; allocate `new Position(fileScope, ctx.index - 1)`
only inside the matching branch. No suffix -> CharIn fails fast, no Position.
Also drops the `.map(_(0))` Char step. Parse output (positions/errors) is
unchanged.
Result:
JMH ParserBenchmark (-f0, same-session): 1.560 -> 1.530 ms/op (+1.9%). Native
parse_time on kube-prometheus: non-regressing, min/p25 ~2% lower (noise-limited
on a loaded machine). Output byte-identical. 517/517 tests pass.
Motivation: std.manifestJson* render fully in memory via FastMaterializeJsonRenderer. The inherited flushCharBuilder spilled the CharBuilder to the output writer at every sub-tree boundary, adding buffer-to-buffer copies that are pure overhead when the whole document is built in memory and emitted once. Modification: - Override flushCharBuilder to write out only when depth == 0 (root finished); accumulate everything in elemBuilder until then. - Size StringBuilderWriter's initial buffer at 4096 (was 16) to cut early reallocations, and mark it private[sjsonnet]. Result: Fewer intermediate copies on the manifestJson* path; output byte-identical.
…Chars ascii mask Adds regression coverage: - object_remove_key_directional: objectRemoveKey interaction with super / addSuper (`a+:`) merge and inline addSuper asserts. - strip_chars_ascii_mask_directional: stripChars over the ASCII range.
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Superseded — split into focused, independently-measured PRs off current master (each output byte-identical, no benchmark code):
The manifest-JSON rendering work this PR was based on is already in master (da92dd1). Closing in favor of the smaller PRs above. |
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Motivation
std.manifestJson,std.manifestJsonMinified, andstd.manifestJsonExstill routed throughStringWriter, payingStringBuffersynchronization perwriteand perflushon the hot manifestation path. Source-built jrsonnet comparisons showed sjsonnet trailing on object-heavy manifest workloads.Modification
StringBuilderWriter: an unsynchronizedWriterover aStringBuilder.FastMaterializeJsonRendererbacked byStringBuilderWriter; route the threestd.manifestJson*builtins through it. PublicMaterializeJsonRendererABI/shape unchanged.UnicodeHandlingTestsextended for the prefix-ordering case.Result
Scala Native hyperfine on kube-prometheus,
-N -w 4 -m 20, jrsonnet HEAD2d7eed05:manifestJsonEx, sjsonnetmanifestJsonEx, jrsonnetJMH regression post-PR:
manifestJsonEx0.055 ms/op,realistic243.6 ms/op,gen_big_object0.842 ms/op.Related: #666.
Test plan
./mill __.reformat./mill -j 1 __.test— 517/517 passFollow-up stacked optimizations
Each commit below was verified for byte-identical output and measured before landing. Perf bar: JVM-positive and Native-non-regressing (changes that measured neutral/negative on Native — a YAML-renderer swap, a binary-operator Position deferral, and a first char-deboxing attempt — were measured and dropped).
skip escape scan for AsciiSafeStrVal.AsciiSafeStrwithout the SWAR escape scanunsynchronized StringBuilderWriter in TomlRendererStringBuffersync on themanifestTomlExpathcapture parse Position without boxingParser.Poswrites thePositionstraight into fastparsesuccessValueinstead ofIndex.map(no Int box/unbox/closure per node)defer Position alloc in exprSuffix2Positiononly on a matched suffix, not on every rep-terminating attemptflush FastMaterializeJsonRenderer only at root depthdepth == 0; 4 KB initial bufferMethodology: JVM via JMH (
ParserBenchmark, plus isolated render benches added underbench/); Native via the binary's--debug-statsphase timing and interleaved hyperfine on kube-prometheus (cooled, min/p25). Render micro-wins (AsciiSafeStr) do not transfer to Native end-to-end because parse+eval dominate there; the parse-side and TOML changes do.