Add option --drop-sampling-log to not keep the sampling log

Fixes #67

src/config.rs

@@ -408,7 +408,20 @@ pub struct RunCommand {
     #[clap(short('p'), long, default_value = "128", value_name = "COUNT")]
     pub concurrency: NonZeroUsize,
 
-    /// Throughput sampling period, in seconds.
+    /// Sampling period, in seconds.
+    ///
+    /// While running the workload, periodically takes a snapshot of the statistics
+    /// and records it as a separate data point in the log. At the end, the log gets saved to
+    /// the final report. The sampling log can be used later for generating plots
+    /// or HDR histogram logs for further detailed data analysis.
+    ///
+    /// Sampling period does not affect the value of the final statistics computed
+    /// for the whole run. You'll not get more accurate measurements by sampling more frequently
+    /// (assuming the same total length of the run).   
+    ///
+    /// The sampling log is used for analyzing throughput fluctuations and the number of samples
+    /// does affect the accuracy of estimating the throughput error to some degree.
+    /// The throughput error estimate may be inaccurate if you collect less than 10 samples.  
     #[clap(
         short('s'),
         long("sampling"),
@@ -417,6 +430,17 @@ pub struct RunCommand {
     )]
     pub sampling_interval: Interval,
 
+    /// Doesn't keep the sampling log in the report
+    ///
+    /// Use this option when you want to run the workload for a very long time, to keep memory
+    /// usage low and steady. The sample log will still be printed while running, but its data won't
+    /// be kept in memory nor saved to the final report.
+    ///
+    /// Caution: you will not be able to later generate plots nor HDR histogram logs from the
+    /// report if you enable this option.   
+    #[clap(long)]
+    pub drop_sampling_log: bool,
+
     /// Label that will be added to the report to help identifying the test
     #[clap(long("tag"), value_delimiter = ',')]
     pub tags: Vec<String>,

src/exec.rs

@@ -179,6 +179,7 @@ pub async fn par_execute(
     sampling: Interval,
     workload: Workload,
     show_progress: bool,
+    keep_log: bool,
 ) -> Result<BenchmarkStats> {
     if exec_options.cycle_range.1 <= exec_options.cycle_range.0 {
         return Err(LatteError::Configuration(format!(
@@ -202,7 +203,7 @@ pub async fn par_execute(
     let progress = Arc::new(StatusLine::with_options(progress, progress_opts));
     let deadline = BoundedCycleCounter::new(exec_options.duration, exec_options.cycle_range);
     let mut streams = Vec::with_capacity(thread_count);
-    let mut stats = Recorder::start(rate, concurrency);
+    let mut stats = Recorder::start(rate, concurrency, keep_log);
 
     for _ in 0..thread_count {
         let s = spawn_stream(

src/main.rs

@@ -203,6 +203,7 @@ async fn load(conf: LoadCommand) -> Result<()> {
         config::Interval::Unbounded,
         loader,
         !conf.quiet,
+        false,
     )
     .await?;
 
@@ -265,6 +266,7 @@ async fn run(conf: RunCommand) -> Result<()> {
             Interval::Unbounded,
             runner.clone()?,
             !conf.quiet,
+            false,
         )
         .await?;
     }
@@ -294,6 +296,7 @@ async fn run(conf: RunCommand) -> Result<()> {
         conf.sampling_interval,
         runner,
         !conf.quiet,
+        !conf.drop_sampling_log,
     )
     .await
     {

src/stats.rs

@@ -294,13 +294,18 @@ pub struct Recorder {
     log: Vec<Sample>,
     rate_limit: Option<f64>,
     concurrency_limit: NonZeroUsize,
+    keep_log: bool,
 }
 
 impl Recorder {
     /// Creates a new recorder.
     /// The `rate_limit` and `concurrency_limit` parameters are used only as the
     /// reference levels for relative throughput and relative parallelism.
-    pub fn start(rate_limit: Option<f64>, concurrency_limit: NonZeroUsize) -> Recorder {
+    pub fn start(
+        rate_limit: Option<f64>,
+        concurrency_limit: NonZeroUsize,
+        keep_log: bool,
+    ) -> Recorder {
         let start_time = SystemTime::now();
         let start_instant = Instant::now();
         Recorder {
@@ -325,6 +330,7 @@ impl Recorder {
             request_latency: LatencyDistributionRecorder::default(),
             throughput_meter: ThroughputMeter::default(),
             concurrency_meter: TimeSeriesStats::default(),
+            keep_log,
         }
     }
 
@@ -356,6 +362,9 @@ impl Recorder {
         if self.errors.len() < MAX_KEPT_ERRORS {
             self.errors.extend(sample.req_errors.iter().cloned());
         }
+        if !self.keep_log {
+            self.log.clear();
+        }
         self.log.push(sample);
         self.log.last().unwrap()
     }
@@ -381,6 +390,10 @@ impl Recorder {
         let concurrency = self.concurrency_meter.mean();
         let concurrency_ratio = 100.0 * concurrency.value / self.concurrency_limit.get() as f64;
 
+        if !self.keep_log {
+            self.log.clear();
+        }
+
         BenchmarkStats {
             start_time: self.start_time.into(),
             end_time: self.end_time.into(),