wherewent

Where did the time go? Find out in one command.

A zero-config recorder that answers "why did this Python batch job take so long?"

Run it from your shell — or as an MCP server an AI agent invokes directly.

wherewent run python your_job.py

The 0.4ms query that costs you 5 minutes

A query can be individually fast — 0.4ms — and still sink your job, because it's called 500,000 times from a single line of code. Your app burns 300 seconds on round-trips while Postgres itself only worked for 80. Every profiler you've tried shows you "time spent in psycopg" and stops there.

wherewent shows you the calling pattern. It groups queries by shape, counts how often each shape ran, sums the wall time, and points at the exact file:line in your code that fired it — then tells you, in plain English with the arithmetic shown, what to do about it.

====================================================================================================
wherewent — SQL flight recorder
----------------------------------------------------------------------------------------------------
wall: 26.15s   cpu: 25.41s (97% CPU busy)   queries: 20,004   commits: 20,001   rollbacks: 1
in-DB time: 5.46s (20.9% of wall; app-observed: includes network+driver+server)
commit time: 9.06s   total rows: 20,000
recording added ~1.81s (~6.9% of wall)
====================================================================================================
QUERY GROUP                                         CALLS     TOTAL     MEDIAN  CALL SITE
----------------------------------------------------------------------------------------------------
INSERT INTO events (name, value) VALUES (?, ?)     20,000     5.46s     0.24ms  demo/naive_job.py:65 in main
SELECT count(*) AS count_1 FROM events                  1     0.00s     0.16ms  demo/naive_job.py:71 in main
====================================================================================================
FINDINGS
----------------------------------------------------------------------------------------------------
1. [R1+R2] commit-per-row loop
   20,000 calls x 0.24ms median ~= 5.5s = 21% of 26.1s wall, at demo/naive_job.py:65. Batch it.
   20,001 commits for 20,000 rows (1.0 rows/commit), 9.1s in commit = 35% of wall. Batch to 1,000+ rows/txn.
   ~= 14.5s attributable
====================================================================================================

Related MCP server: tokensave

Why it's different

Install

pip install wherewent

That's it — the recorder is pure standard library. You only need SQLAlchemy because your job already uses it.

Use it

Wrap any command. Your script runs completely unmodified — no imports, no decorators, no config:

wherewent run python your_job.py --some arg
wherewent run python -m your_package
wherewent run --save run.json python your_job.py   # also dump machine-readable JSON

• The report prints to stderr at exit; your job's own stdout/stderr pass through untouched.

• Ctrl-C still produces a report. Sampling the first 5 minutes of a 14-hour job is the main use case — partial data is the point.

• Peek without stopping. Send SIGUSR1 (kill -USR1 <pid>) for a partial snapshot mid-run, or run with WHEREWENT_INTERVAL=30 to print one every 30s. The job keeps going.

• Works on async SQLAlchemy. Queries run inside a greenlet with no user frames on the stack, so naive stack-walking blames nothing; wherewent attributes them to your real call site anyway (AsyncSession / AsyncConnection).

• It can never crash or corrupt your job. Every hook body is wrapped so the recorder fails silent rather than taking your run down with it.

• It never records your data. Only query shapes and counts are kept — literal values and bind parameters are stripped before anything is stored.

Try the built-in demo

git clone https://github.com/habibafaisal/wherewent && cd wherewent
pip install -e ".[dev]"
wherewent run python demo/naive_job.py     # watch the R1+R2 finding fire
python demo/benchmark.py                    # naive vs fixed, with the overhead gate

Use it as an MCP server (agent-native)

wherewent ships a Model Context Protocol (MCP) server, so an AI agent can invoke it directly the moment a job is slow and get back machine-readable findings — instead of reading raw query logs and reasoning its way to the same conclusion. It is listed in the official MCP Registry as io.github.habibafaisal/wherewent.

Install with the [mcp] extra (this pulls in the MCP SDK; the core recorder stays pure-stdlib) and run the stdio server:

uvx --from 'wherewent[mcp]' wherewent-mcp
# or:  pip install 'wherewent[mcp]'  &&  wherewent-mcp

Transport: stdio. Tools exposed:

Each finding carries fix, call_site, calls, wall_fraction, and an evidence object an agent can act on and cite. Wire it into any MCP client (e.g. Claude Desktop) via config:

{
  "mcpServers": {
    "wherewent": {
      "command": "uvx",
      "args": ["--from", "wherewent[mcp]", "wherewent-mcp"]
    }
  }
}

A Dockerfile at the repo root builds this same stdio server for container-based MCP hosts.

Name your unit of work

"81,749 queries" is hard to judge. "135 queries per receivable" tells an engineer instantly that the architecture is chatty. Name the unit your job processes and wherewent reports the economics of one — median duration, queries/commits/rows per unit, and how the cost trends as the run progresses:

# Zero-config: name a function; every top-level call is one unit
wherewent run --unit-function myapp.jobs:process_receivable python run.py

# Or mark the unit in code (same machinery, same report)
import wherewent
for receivable in book:
    with wherewent.unit("receivable"):
        process(receivable)

UNIT: myapp.jobs:process_receivable   (1,203 units)
----------------------------------------------------------------------------------------------------
  median duration    341 ms         queries/unit    135 (median)
  commits/unit       1.0            rows/unit       46.0
  GROWTH
    units 1–100          220 ms/unit
    units (last 100)     379 ms/unit
    queries 1–100        98 queries/unit
    queries (last 100)   171 queries/unit
    trend                +72% slower over the run
    query trend          +74% more queries/unit over the run     ← R6 fires

R6 fires on either slope. That matters for a compute-bound job: if the clock stays flat but queries/unit climbs, the duration trend reads flat and only the query trend exposes the problem — so wherewent reports both and says plainly that the pattern is a scalability risk rather than the current wall-clock bottleneck.

The growth trend is why a sampled run is honest: it shows cost-per-unit rising, so you know the full run will be worse than a linear extrapolation — the thing a totals-only profiler can never tell you. Per-unit counts are exact even under concurrent async units; nothing but shapes and counts is ever recorded.

How it works

1. Injects itself into the target process via a PYTHONPATH sitecustomize shim — no changes to your code, no wrapper imports.

2. Listens at the class level — event.listen(sqlalchemy.engine.Engine, ...) — so every engine your app creates is captured automatically, config-free.

3. Normalizes each statement into a query group: literals, bind params, IN-lists and multi-row VALUES collapse, so a million distinct inserts become one honest row.

4. Resolves the call site by walking the stack past library frames to the first line of your code — cheaply: cached by filename, full stacks only for the first 5 samples per group, so the hot path stays cheap enough to hit its overhead budget.

5. Fires deterministic findings from three rules, each showing its arithmetic.

The findings engine

Findings that share a root cause merge (e.g. R1+R2), everything under 5% of wall is suppressed, and at most the top 3 are shown — ranked by seconds attributable. R4 catches the case a per-group threshold can't: an N+1 pattern spread across a SELECT + UPDATE + INSERT that individually look innocent but fire as one unit each loop — and, since v0.3, it fires on patterns that scale even when one-time setup costs make them look small on a short sample run.

Every number is honest. Query times are labelled app-observed (they include network, driver, and server time — not just Postgres). Anything that can't be measured prints —, never a guess. wherewent even times its own hooks and reports the overhead it added.

Roadmap — help wanted 🙌

wherewent is built to grow beyond SQLAlchemy. Seven of its eight modules — normalization, call-site resolution, the stats model, the rules engine, the report, the CLI, and the injection shim — are already framework-agnostic. They operate on a plain RunSnapshot of query events. Only recorder.py, which binds SQLAlchemy's event system, is framework-specific.

That means a new backend is a well-contained contribution: capture query start/end/rowcount/txn events from another driver, feed the same RunSnapshot, and the entire findings-and-report pipeline works for free. Good first backends:

• Async SQLAlchemy — call-site attribution through the greenlet boundary (v0.2.0)

• Work-unit-aware profiling — per-unit economics + growth trend (v0.3.0)

• Execution-pattern findings (the next big one — help wanted) — today wherewent clusters the queries that fire together each iteration (R4). Next: reconstruct the ordered, possibly nested workflow behind them and name it, e.g.

  For each receivable:
    For each audit event ×23:
      SELECT chain_state → SELECT payload → INSERT payload → INSERT audit_event → UPDATE chain_state
  Finding: serialized audit-append loop — 23 repetitions/receivable, ≈115 statements/receivable,
           58% of DB activity, at process_receivable → emit_firing → append_event.

  This is a real step past ordinary N+1 detection (Sentry/Scout find repeated single-shape queries; this would find multi-operation workflows spanning several SQL shapes and functions): read→modify→write loops, serialize→insert→commit per item, whole-state snapshots after every mutation, growing-history scans, and CPU rising with item position. Needs an ordered per-unit event log + repeated-subsequence mining, kept under the overhead gate.

• Raw psycopg / psycopg2 — cursor subclass or connection factory hook

• Raw asyncpg (outside SQLAlchemy) — the async execution path

• Django ORM — via connection.execute_wrapper

• Generic DB-API 2.0 — a monkeypatch-free Cursor proxy

• More findings rules (lock-wait, seq-scan heuristics)

See CONTRIBUTING.md for the backend contract and the < 15% overhead gate that every capture path must pass.

Limitations (today)

• SQLAlchemy 2.x (sync and async ORM/Core; 1.4 may work). Raw asyncpg outside SQLAlchemy is not attributed yet.

• Single process — no multiprocessing fan-out.

• Query times are app-observed (network + driver + server), by design.

• Commit timing is obtained by wrapping the dialect's commit; if that wrap fails it prints —.

• Per-iteration ratios are estimates (labelled ≈) inferred from co-occurring query counts — shown only when the signal is strong, never guessed.

• Per-unit counts (--unit-function / wherewent.unit()) are exact even under concurrent async units; per-unit duration is wall time and may overlap when units run concurrently — the common sequential-loop case is exact.

• R6's attributed seconds are a deterministic lower-bound estimate, not a measurement. The excess queries per unit are priced at the run's mean per-query DB time, so if the extra queries are cheaper than average the true cost is higher (and vice versa). It is computed from exact integer query counts rather than the clock, so it is reproducible run to run — but R6's claim is the slope, not the seconds.

• ORM flush attribution. Queries emitted by a session.flush()/commit() all resolve to that one call site, so R4 can group unrelated writes under a single "workflow". When a cluster's writes share one source line, wherewent labels it as possibly a single flush rather than claiming you can collapse it — it will not tell you to batch something already batched.

• Per-group median is a bounded sample median (reservoir of 5,000 executions per group) so memory stays flat on million-query runs. calls and total_time remain exact.

• Commit vs rollback time are reported separately. SQLAlchemy's pool issues a rollback on every connection check-in, so rollback time is labelled (incl. pool resets) and is never folded into commit time.

• Findings describe where the time goes and how it scales — on a CPU-bound run they say so explicitly, rather than implying that fixing the SQL will speed up this run.

These are the honest edges of a validation prototype, not permanent walls — see the roadmap.

Contributing

Contributions are very welcome — new backends, new rules, docs, bug reports. Start with CONTRIBUTING.md, open an issue to discuss anything substantial, and run pytest && python demo/benchmark.py before you push.

License

MIT © 2026 Habiba Faisal