r/bigquery • u/vinteralex24 • 10h ago
I analyzed 27k BigQuery jobs to find what actually drives the bill. 68% of it was one query pattern.
Ran a cost analysis over a 30-day window on a production project — 27,076 jobs, 45.1 TB billed, ~$282 in query cost. Anonymized.
Methodological caveat first, because it matters: BigQuery doesn't report bytes per table, so a job's entire scan gets counted against every table it references. Rank with that column, never sum it. Same for the findings below — they overlap, one query can trigger three rules. Don't add them up.
The interesting part: the project was spending ~$2.30/day. On 25 August it jumped to ~$25/day and stayed there.
Cause: one query pattern, executed 2,638 times in 30 days, billing 30.8 TB. On its own that's $192 — 68% of the entire month's query cost.
Not a badly written query. A good one running far too often.
What else showed up:
- 633 queries used
SELECT *on tables over 1 GB → 4.0 TB. BigQuery bills the columns you read, not the rows you return. - 2,214 queries scanned 10 GB+ with no
LIMIT→ 34.8 TB. - 126 queries read a partitioned table without its partition filter → every partition scanned instead of the few needed.
- 42 queries ran 10+ times and re-billed 40.9 TB — the result cache only helps while the underlying data is unchanged.
The part that surprised me: 98% of query spend came from a single service account — the dbt runner. Nobody was being careless. It was a pipeline doing exactly what it was told, at a scale nobody was watching.
Which is the real problem with warehouse bills. The invoice tells you the total. It never tells you that one model, executed 2,638 times, is two-thirds of it.
Everything above comes from INFORMATION_SCHEMA.JOBS_BY_PROJECT — bytes billed, who ran it, what it referenced. No table data is read.
I built a small read-only tool around this — self-hosted, metadata-only, nothing leaves your machine.
That project's report is confidential, so I can't share it. What I can share is a sample the tool generates from built-in synthetic data — nothing in it is real, but the format and the findings are exactly what you get: [sample_report]
