deploy/bench/overhead.sh - master - rustwizard/pgtrace

deploy/bench/overhead.sh
93 строки3 KB
Rust Wizard
bench: report median overhead and add stable-measurement hints
07 авг 2026, 14:59
07 авг 2026, 14:5996029dc
#!/usr/bin/env bash
# Measures pgtrace overhead: pgbench TPS with and without the agent running.
#
# Run on the Lima VM:
#   limactl shell ebpf-dev -- sudo bash deploy/bench/overhead.sh
#
# The agent must not be running already (the script starts and stops it).
set -euo pipefail

REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
PG_BENCH="${PG_BENCH:-$(command -v pgbench 2>/dev/null || echo /usr/lib/postgresql/16/bin/pgbench)}"
DB="${PG_BENCH_DB:-pgbench}"
DURATION="${PG_BENCH_T:-30}"
CLIENTS="${PG_BENCH_C:-8}"
JOBS="${PG_BENCH_J:-4}"
RUNS="${PG_BENCH_RUNS:-3}"
THRESHOLD="${PG_BENCH_THRESHOLD:-1ms}"

run_pgbench() {
    "$PG_BENCH" -c "$CLIENTS" -j "$JOBS" -T "$DURATION" "$DB" 2>&1 |
        grep -oE "tps = [0-9.]+" | awk '{print $3}'
}

mean() {
    awk '{ s += $1; n++ } END { printf "%.1f", s / n }'
}

median() {
    sort -n | awk '
        { a[NR] = $1 }
        END {
            mid = int((NR + 1) / 2)
            if (NR % 2 == 1) printf "%.1f", a[mid]
            else printf "%.1f", (a[mid] + a[mid + 1]) / 2
        }'
}

start_agent() {
    cd "$REPO"
    sudo ./bin/pgtrace agent \
        --dsn "postgres://$USER:$USER@localhost/$DB" \
        --threshold "$THRESHOLD" \
        --window 10s \
        --http :19092 > /tmp/pgtrace-overhead.log 2>&1 &
    AGENT_PID=$!
    sleep 2
}

stop_agent() {
    if [[ -n "${AGENT_PID:-}" ]]; then
        sudo kill -INT "$AGENT_PID" 2>/dev/null || true
        wait "$AGENT_PID" 2>/dev/null || true
    fi
}
trap stop_agent EXIT

echo "== baseline (no agent) =="
BASELINE=()
for _ in $(seq "$RUNS"); do
    BASELINE+=("$(run_pgbench)")
done

echo "== with agent (threshold $THRESHOLD) =="
start_agent
AGENT=()
for _ in $(seq "$RUNS"); do
    AGENT+=("$(run_pgbench)")
done
stop_agent
AGENT_PID=

echo
printf "%-12s %-20s %-20s\n" "run" "baseline tps" "with agent tps"
for i in $(seq "${#BASELINE[@]}"); do
    printf "%-12d %-20s %-20s\n" "$i" "${BASELINE[$((i-1))]}" "${AGENT[$((i-1))]}"
done

BASE_MEAN="$(printf '%s\n' "${BASELINE[@]}" | mean)"
AGENT_MEAN="$(printf '%s\n' "${AGENT[@]}" | mean)"
BASE_MEDIAN="$(printf '%s\n' "${BASELINE[@]}" | median)"
AGENT_MEDIAN="$(printf '%s\n' "${AGENT[@]}" | median)"
OVERHEAD_MEDIAN="$(awk -v b="$BASE_MEDIAN" -v a="$AGENT_MEDIAN" 'BEGIN { printf "%.2f", (b - a) / b * 100 }')"

echo
echo "baseline tps (mean/median):   $BASE_MEAN / $BASE_MEDIAN"
echo "with agent tps (mean/median): $AGENT_MEAN / $AGENT_MEDIAN"
echo "overhead (median):            ${OVERHEAD_MEDIAN}%"
echo
echo "Note: below ~1-2% the difference is within VM noise. For stable numbers:"
echo "  - stop autovacuum/checkpoints during the run:"
echo "      sudo -u postgres psql -c 'ALTER SYSTEM SET autovacuum = off' && sudo systemctl restart postgresql"
echo "  - use a longer run / more repetitions: PG_BENCH_T=60 PG_BENCH_RUNS=5"
echo "  - the median is more robust than the mean against outliers"