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Guide: How to run a simple query performance benchmark at home

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(@infra_skeptic_9)
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Posts: 155
Topic starter   [#19834]

Alright, so the marketing teams have convinced you that their new cloud-native BI tool is "blazingly fast" and "handles petabytes with ease." They're all shouting about their in-memory engines and magic columnar compression. Wonderful. Before you sign that enterprise contract that costs more than your team's annual coffee budget, maybe you should see what that performance *actually* looks like on your data, on your network, with your users' typical nonsense queries.

This isn't about building a perfect, lab-grade benchmark. This is about creating a *sufficiently painful* reality check. You need a controlled way to generate comparable frustration across platforms. Forget the vendor's cherry-picked demo dataset. You'll use a sample of your own data, or a synthetic dataset that mimics your worst-case tableβ€”think 50 million rows with a few hundred columns, some nested JSON, and a couple of timestamp fields to really make the join optimizers sweat.

Here's the skeleton of a process you can run in an afternoon. The goal is to produce a simple table of cold-start vs cached query times, memory bloat, and cost per query (if you're feeling spicy). We'll use a simple, scriptable approach.

**Step 1: The Data & The Queries**
First, get your test dataset into a format you can push to each platform. A CSV or Parquet file in an S3 bucket is universal bait. Now, craft 5-7 queries that represent real patterns:
1. A simple `SELECT * FROM table LIMIT 10` (connection/simple scan).
2. A multi-column filter with a date range.
3. A basic aggregation (GROUP BY on a low-cardinality column).
4. A nasty multi-table JOIN (if applicable).
5. A complex aggregation with a window function.
6. A "wide" query pulling 100+ columns.
Write these as raw SQL. This is your torture test suite.

**Step 2: The Automation Script**
You need a script to run these queries sequentially, capture latency, and note any errors. Here's a crude Python example using `psycopg2` (adapt client library per BI tool's SQL endpoint). The key is to run each query multiple times, discarding the first (cold) run.

```python
import time
import psycopg2
import csv

queries = [
"SELECT * FROM test_table LIMIT 10;",
"SELECT customer_id, SUM(amount) FROM test_table WHERE date > '2023-01-01' GROUP BY customer_id;",
# ... your other queries
]

conn = psycopg2.connect(host="your-bi-tool-endpoint", ...)
cur = conn.cursor()

results = []

for i, query in enumerate(queries):
times = []
for iteration in range(5): # 5 runs per query
start = time.perf_counter()
cur.execute(query)
_ = cur.fetchall() # force full result fetch
elapsed = time.perf_counter() - start
if iteration > 0: # discard first run (cold cache/compilation)
times.append(elapsed)
time.sleep(1) # brief pause
avg_time = sum(times) / len(times) if times else 0
results.append({"query_num": i, "avg_time": avg_time, "query": query[:50]})
print(f"Query {i}: Cold {times[0] if len(times)>1 else 'N/A'}s, Avg Warm {avg_time:.2f}s")

cur.close()
conn.close()

# Write results to CSV for comparison
with open('benchmark_results.csv', 'w') as f:
writer = csv.DictWriter(f, fieldnames=['query_num', 'avg_time', 'query'])
writer.writeheader()
writer.writerows(results)
```

**Step 3: The Setup & The Gotchas**
Spin up identical-sized datasets in each BI tool you're evaluating (e.g., Power BI Premium dataset, a Looker persistent derived table, a Redshift cluster, a QuickSight SPICE dataset). Use the smallest viable instance size for eachβ€”this isn't about max performance, it's about performance *per dollar*. Run the script against each.

Now, the critical part: observe what the tools *don't* show you.
* Did one tool's memory usage balloon and not release after the window function query?
* Did another tool have a 30-second "compilation" time on the first query but then cache everything, masking real-world variability?
* How much effort was it to get the data in and the SQL endpoint exposed? Was it a 2-hour Terraform module or a 2-day support ticket?

**Step 4: The Uncomfortable Math**
Take the average warm query time across all your test queries. Multiply by your estimated monthly query volume. Now look at the monthly invoice for each platform. Calculate the cost per second of query execution. You'll often find that the "slower" tool on a per-query basis is orders of magnitude cheaper, making its total cost of operation actually sensible. Or you might find the opposite, and the expensive tool justifies its price. The point is you'll know, with your own data, instead of trusting a glossy datasheet.

Do this. It's a few hours of work that will save you from a multi-year commitment to a platform that's optimised for a reality you don't live in. Then you can come back here and tell us all which tool failed spectacularly.

-- cynical ops


Your k8s cluster is 40% idle.


   
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