From caa556f0f0e37e396e53626132698834c6e69813 Mon Sep 17 00:00:00 2001
From: Ilja Heitlager <iheitlager@schubergphilis.com>
Date: Sun, 30 Aug 2026 10:39:12 +0200
Subject: [PATCH] perf: inline hot varint/cell decode calls on the SeekRowid
 binary-search path (#657)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Profiling with `sample` on the read_join bench (16700-row bench_data
joined to bench_lookup on its PK) showed 56% of samples landing in
TableCursor::seek's binary search — decode_varint, decode_cell_head,
and read_cell_pointer were compiled as real (non-inlined) function
calls, paid twice per probed cell across ~8-9 binary-search probes per
row against bench_lookup's ~230-cell leaf pages. read_full_scan, which
never calls seek(), was already faster than the oracle (0.71x),
confirming the gap was isolated to this path rather than general
record decode.

Marking these three small, always-hot functions #[inline] lets LTO
fold them into the binary-search loop. read_join drops from 3.63ms to
2.95ms (measured via `cargo bench --bench crud -- read_join`), closing
the oracle gap from 1.9x to 1.5x.

spend: ~1.5x estimate (initial profiling pointed to diffuse overhead
with no fix; a second pass comparing read_join against read_full_scan
and the compiled opcode stream against oracle's EXPLAIN output pinned
the actual hot loop).
---
 src/btree.rs         | 2 ++
 src/record/varint.rs | 1 +
 2 files changed, 3 insertions(+)

diff --git a/src/btree.rs b/src/btree.rs
index b4fd4c9e..6d895a89 100644
--- a/src/btree.rs
+++ b/src/btree.rs
@@ -1654,6 +1654,7 @@ fn read_u32(page: &[u8], offset: usize, page_num: u32) -> Result<u32, BtreeError
     Ok(u32::from_be_bytes(bytes))
 }
 
+#[inline]
 fn read_cell_pointer(
     page: &[u8],
     ptr_off: usize,
@@ -1686,6 +1687,7 @@ fn cell_ptr_offset(base: usize, i: usize) -> usize {
 /// Decodes a leaf table-b-tree cell's head (payload-length varint + rowid
 /// varint) and returns `(rowid, payload_len, tail_start)`, where
 /// `tail_start` is the page offset where the payload bytes begin.
+#[inline]
 fn decode_cell_head(
     page: &[u8],
     cell_start: usize,
diff --git a/src/record/varint.rs b/src/record/varint.rs
index 7502f295..7a86fb7f 100644
--- a/src/record/varint.rs
+++ b/src/record/varint.rs
@@ -10,6 +10,7 @@ use super::error::RecordError;
     clippy::arithmetic_side_effects,
     reason = "i ranges over the compile-time-constant 0..8, so i + 1 never overflows"
 )]
+#[inline]
 pub fn decode_varint(buf: &[u8]) -> Result<(u64, usize), RecordError> {
     let mut result: u64 = 0;
     for i in 0..8 {