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Avoid Vec+join in jq Replace/Append (DSK-137) #178

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Merged
daisuke8000 merged 1 commit into from
Jul 5, 2026
Merged

Avoid Vec+join in jq Replace/Append (DSK-137) #178

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30 changes: 17 additions & 13 deletions crates/rustern-core/src/pipeline/jq_evaluate.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,11 @@
use std::sync::Arc;

use futures::stream::{Stream, StreamExt};
use jaq_core::data::JustLut;
use jaq_core::load::{Arena, File, Loader};
use jaq_core::{Compiler, Ctx, Filter, Vars};
use jaq_json::Val;
use std::fmt::Write as _;
use std::sync::Arc;

use futures::stream::{Stream, StreamExt};

use crate::source::{LogEvent, LogSourceError};

Expand All @@ -23,6 +24,17 @@ pub enum QueryMode {
Filter,
}

fn format_outputs_joined(outputs: &[Val]) -> String {
let mut rendered = String::new();
for (i, v) in outputs.iter().enumerate() {
if i > 0 {
rendered.push('\n');
}
let _ = write!(rendered, "{v}");
}
rendered
}
Comment on lines +27 to +36

@coderabbitai coderabbitai Bot Jul 5, 2026

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🚀 Performance & Scalability | 🔵 Trivial | 💤 Low value

軽微: 容量事前確保でホットパスの再割当てを削減可能

String::new() は初期容量ゼロのため、要素数が多い場合に複数回の再割当てが発生し得ます。パイプラインのホットパスにおける per-line allocation 最適化が本PRの目的なので、with_capacity によるヒントもついでに検討すると良さそうです。

As per path instructions, "Performance on hot paths (per-line allocations, regex reuse)" が pipeline ディレクトリの重点項目です。

♻️ 提案 
 fn format_outputs_joined(outputs: &[Val]) -> String {
-    let mut rendered = String::new();
+    let mut rendered = String::with_capacity(outputs.len() * 16);
     for (i, v) in outputs.iter().enumerate() {
         if i > 0 {
             rendered.push('\n');
         }
         let _ = write!(rendered, "{v}");
     }
     rendered
 }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
fn format_outputs_joined(outputs: &[Val]) -> String {
let mut rendered = String::new();
for (i, v) in outputs.iter().enumerate() {
if i > 0 {
rendered.push('\n');
}
let _ = write!(rendered, "{v}");
}
rendered
}
fn format_outputs_joined(outputs: &[Val]) -> String {
let mut rendered = String::with_capacity(outputs.len() * 16);
for (i, v) in outputs.iter().enumerate() {
if i > 0 {
rendered.push('\n');
}
let _ = write!(rendered, "{v}");
}
rendered
}
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/rustern-core/src/pipeline/jq_evaluate.rs` around lines 27 - 36, The
hot-path formatter in format_outputs_joined currently starts with String::new(),
which can trigger repeated reallocations as outputs grow. Update this helper to
preallocate the buffer with an appropriate capacity hint using with_capacity,
based on the expected number of Val items and separators, while keeping the
existing join logic in place. Focus the change inside format_outputs_joined so
the per-line allocation behavior in jq_evaluate is reduced without altering the
rendered output.

Source: Path instructions


#[derive(Clone)]
pub struct CompiledFilter {
inner: Arc<Filter<JustLut<Val>>>,
Expand Down Expand Up @@ -105,21 +117,13 @@ where
}
QueryMode::Replace => {
ev.structured = None;
let rendered = outputs
.iter()
.map(|v| format!("{v}"))
.collect::<Vec<_>>()
.join("\n");
let rendered = format_outputs_joined(&outputs);
ev.message = Arc::from(rendered.as_str());
Some(Ok(ev))
}
QueryMode::Append => {
ev.structured = None;
let rendered = outputs
.iter()
.map(|v| format!("{v}"))
.collect::<Vec<_>>()
.join("\n");
let rendered = format_outputs_joined(&outputs);
ev.message =
Arc::from(format!("{} | {}", ev.message, rendered).as_str());
Some(Ok(ev))
Expand Down