Additional debug logging on onestop_id resolution

[irees]

Summary

Adds temporary, opt-in instrumentation to measure how often the allow_previous_onestop_ids stop resolution actually does work beyond an exact Onestop ID lookup, and how much of that work a content-based (geohash point + name) search would reproduce. This is decision-support for interline-io/tlv2#354, which is evaluating whether the feed_version_stop_onestop_ids history table (~640 GB in production, the bulk of it per-feed-version repetition) can be replaced by a search-key resolver without losing real resolutions. The instrumentation is gated behind an environment variable, off by default with zero overhead, read-only, and intended to be removed once the measurement window is complete.

What it measures

For each resolved current stop, it classifies two things: differs — the stop's current Onestop ID is not the one that was requested, meaning an exact lookup would have missed it and the previous-id behavior did real work; and search_would_match — whether a geohash-point + name-similarity search (using the same 100 m radius and 0.4 word_similarity threshold a candidate search-key resolver would use) would also have found the stop. The decision metric is n_meaningful = differs AND NOT search_would_match: resolutions that only stored history can recover. If that count stays near zero over real traffic, a search-key resolver is safe; if not, it quantifies the recall a search-only design would lose.

How it works

A probe in FindStops fires only when TL_LOG_ALLOWPREV_PROBE is set and the request is a bare-osid previous-id lookup — allow_previous_onestop_ids true, no feed_version_sha1, no explicit ids — which isolates the durable-key use case (e.g. a stored Onestop ID powering a departure board) from frontend pinned-version browsing. It runs one additional read-only query that reproduces the same (feed, stop_id) continuity the production resolver uses, then computes both classifications entirely in SQL, using ST_PointFromGeoHash to decode the requested geohash so no Go-side geohash or name-normalization logic is needed. Results are emitted as structured logs: one allowprev_probe summary line per request (n_requested, n_resolved, n_differs, n_meaningful, requested_osids) and one allowprev_probe_meaningful detail line per resolution that only history could recover.

Scope and caveats

Off by default; when the env var is unset there is no added query or overhead. When enabled it adds one synchronous read-only query to qualifying requests, so it is a measurement-window tool rather than a permanent fixture. It measures raw continuity resolution without permission or license filtering, so counts reflect resolution capability rather than what any specific caller would be authorized to see. Pinned-feed-version previous-id requests are intentionally excluded as a different semantic. The whole change is one new file plus an eight-line guard in FindStops, so it is straightforward to delete afterward.

Test plan

Set TL_LOG_ALLOWPREV_PROBE=1 and start the server, then issue a GraphQL stops query with a bare previous Onestop ID, e.g. stops(where:{onestop_id:"s-9q9nfswzpg-fruitvale", allow_previous_onestop_ids:true}), and confirm an allowprev_probe log line is emitted with sensible counts (and an allowprev_probe_meaningful line only when a resolution would not be reproduced by search). Confirm that a request with feed_version_sha1 also set produces no probe line. Unset the env var and confirm no probe log lines appear and no extra query is issued.

[Copilot]

Pull request overview

This PR adds opt-in, temporary instrumentation to quantify how often allow_previous_onestop_ids stop resolution provides value beyond exact Onestop ID lookup, and whether a geohash+name search would have reproduced the same resolutions (decision-support for potentially replacing the history table).

Changes:

• Adds a new diagnostic query + structured logging probe gated by TL_LOG_ALLOWPREV_PROBE.
• Invokes the probe from FindStops only for the “bare Onestop ID + allow_previous_onestop_ids + active feed” request shape.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
server/finders/dbfinder/stop.go	Adds a guarded call to the allow-prev probe for qualifying requests.
server/finders/dbfinder/stop_onestop_probe.go	Implements the diagnostic query and structured logging for allow-prev resolution effectiveness.

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