cpp/bench_mark/README.md

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# C++ Benchmarks

`read_backend_benchmark` compares `PREAD` and `MMAP` without enforcing a
performance threshold. It reports sequential 64 KiB reads, deterministic
random 4 KiB reads, repeated parsing of real TsFile metadata, random bounded
`queryByRow` queries, and one concurrent random-read worker per input file. The
query-planning scan is performed before the timed random-query interval.
Files with no queryable rows still participate in the byte-read and metadata
workloads, but are skipped for the random-query workload.

Build it through the main CMake project so it links the exact SDK under test:

```bash
cmake -S cpp -B cpp/target/read-backend-benchmark \
  -DCMAKE_BUILD_TYPE=Release \
  -DBUILD_BENCHMARK=ON -DBUILD_TEST=OFF -DBUILD_TOOLS=OFF \
  -DTSFILE_BUILD_SHARED=OFF
cmake --build cpp/target/read-backend-benchmark \
  --target read_backend_benchmark --config Release
```

With a single-config generator such as Ninja, the executable is
`cpp/target/read-backend-benchmark/read_backend_benchmark` (plus `.exe` on
Windows). Run it with one or, preferably, several representative TsFiles:

```bash
./read_backend_benchmark data-1.tsfile data-2.tsfile data-3.tsfile
./read_backend_benchmark --mmap-first data-1.tsfile data-2.tsfile data-3.tsfile
```

The second form reverses backend order to expose warm page-cache bias. For
meaningful results, repeat both forms and record filesystem, storage device,
file sizes, compiler flags, and whether the OS page cache was warm. The checksum
makes accidental short reads, metadata-load failures, or optimizer removal
visible; it is not a TsFile-content checksum.