Function run_buffer_cache_diagnostic_case

xtask/src/main.rs:3709–3791

(
    cases: &[SpeedCase],
    id: &str,
    statements: &[&str],
)

}

fn run_buffer_cache_diagnostic_case(
    cases: &[SpeedCase],
    id: &str,
    statements: &[&str],
) -> Result<BufferCacheDiagnosticCase> {
    let target_index = cases
        .iter()
        .position(|case| case.id == id)
        .ok_or_else(|| anyhow!("unknown speed hotspot case {id}"))?;
    let target = &cases[target_index];

    let mut db = Pglite::builder()
        .temporary()
        .open()
        .with_context(|| format!("open buffer-cache diagnostic database for {}", target.id))?;

    let setup_started = Instant::now();
    for setup_case in &cases[..target_index] {
        db.exec(&setup_case.sql, None)
            .with_context(|| format!("run buffer-cache setup case {}", setup_case.id))?;
    }
    let setup_micros = setup_started.elapsed().as_micros();

    let settings = exec_rows_json(
        &mut db,
        "SELECT current_setting('shared_buffers') AS shared_buffers, current_setting('fsync') AS fsync, current_setting('synchronous_commit') AS synchronous_commit, current_setting('wal_buffers') AS wal_buffers, current_setting('work_mem') AS work_mem",
    )?;
    let relation_sizes = exec_rows_json(
        &mut db,
        "SELECT relname, pg_relation_size(oid)::bigint AS bytes FROM pg_class WHERE relname IN ('t1', 't2', 'i2a', 'i2b') ORDER BY relname",
    )?;

    let mut explained = Vec::new();
    for statement in statements {
        if matches!(*statement, "BEGIN" | "COMMIT") {
            let (result, phases) = capture_phase_timings(|| {
                let started = Instant::now();
                let result = db.exec(statement, None);
                (result, started.elapsed())
            });
            let (result, elapsed) = result;
            result.with_context(|| format!("run transaction control statement {statement}"))?;
            explained.push(BufferCacheDiagnosticStatement {
                sql: (*statement).to_owned(),
                elapsed_micros: elapsed.as_micros(),
                explain_rows: serde_json::Value::Null,
                fs_trace: serde_json::Value::Null,
                phases,
            });
            continue;
        }

        reset_fs_trace();
        let explain_sql = format!("EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON) {statement}");
        let (result, phases) = capture_phase_timings(|| {
            let started = Instant::now();
            let result = db.exec(&explain_sql, None);
            (result, started.elapsed())