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Bound the direction precompute shape cache - #1668
DirectionPrecomputer no longer loads every row of the shapes table into one Go map before computing stop directions. It keeps the most recently used shapes up to 500,000 points (about 20 MB of rows) in a small LRU cache, recentShapes, and reads any other shape with the per-shape query the calculator already used. Concurrent lookups of one shape share one read through a singleflight group. The completion log reports shape_cache_hits and shape_reads.
Removed: SetShapeCache, its lock and "initialized" flag (only the precomputer used them), and the GetAllShapes query (no other caller).
Root cause
For NJ Transit bus the all-shapes map held 3.3 million points, and the precompute stage peaked at 1.70 GiB of heap. Once the import stops holding the whole feed (#1669, #1672, #1676), this map would be the process peak. The per-shape query returns the same points in the same order, so stop directions do not change: the RABA table digests, which include stops.direction, are unchanged.
Testing
Test failing on main before this change: n/a (memory change, no behavior change)
heap while precomputing directions (precomputation_batch_written)
954.25 MiB
362.75 MiB
process peak RSS
2.40 GiB
2.39 GiB
import time
18.58s
20.229s
Full per-stage output is in the TestImportMemory log; the table shows the stages this PR moves.
New tests: TestRecentShapesEvictsLeastRecentlyUsedPoints (LRU eviction by point budget, oversized shape kept alone), TestPrecomputeReadsEachShapeOnce (four stops on one shape cause one read, with the expected directions), and a failed read is not cached.
Checklist
This PR addresses one issue.
It is under ~200 changed lines, or the description says why it can't be split.
This PR is not a bug fix, or the new or changed test fails on main and passes on this branch.
Each commit is one logical change with a clear message.
I did not hand-edit sqlc-generated files under gtfsdb/ (db.go, models.go, query.sql.go) or testdata/openapi.yml (synced from upstream).
This PR changes no handler, or handlers pass r.Context() to DB/service calls, not context.Background().
The response comparison above is filled in, or this PR doesn't change a Java-served response.
This PR adds no endpoint, or each new endpoint matches testdata/openapi.yml, has an issue open on OneBusAway/sdk-config, or is outside the SDK and the description says why.
I read every line of this diff and can explain it if asked.
Notes for reviewers
Size. 204 added, 420 removed. Most of the removal is the old all-shapes cache and its tests; the new cache and its tests are about 130 lines. Removing the old cache without the replacement would regress import time.
Trade-off. A feed whose stops visit shapes in a scattered order gets fewer cache hits and a slower precompute (up to the no-cache case, about 31 s instead of 21 s for NJ Transit). It never uses more memory than the budget. The hit/miss log shows whether any real feed needs the work grouped by shape instead.
Summary by CodeRabbit
Performance
GTFS direction calculations now retrieve shape data as needed and reuse recently accessed results, rather than loading all shapes upfront.
Concurrent requests for the same shape share a database read, and recent shape data is kept within a point limit.
Direction precomputation now loads shape points on demand through a point-budgeted LRU cache, coalesces concurrent misses, and records cache statistics. The all-shapes query and the calculator’s preloaded-cache API were removed.
The calculator reads shape points directly when no cache is configured, or uses the cache and coalesces concurrent misses. The all-shapes query and SetShapeCache method are removed.
The precomputer configures a 500,000-point cache and no longer preloads all shape points. Completion logs include cache statistics; tests cover shared reads and retrying failed reads.
No identified regression remains to resolve before merging; normal checks still apply.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
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Explanation
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Docstring Coverage
Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
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Explanation
Title check
The title "Bound the direction precompute shape cache" matches the main change: DirectionPrecomputer now uses a point-budgeted LRU cache (recentShapes, capped at 500,000 points) in place of the full-t…
Description check
The description follows the repository template: it has the template marker, a 'Part of #1657' reference, 'What it does', 'Root cause', 'Testing' (with the failing-on-main line and manual check filled…
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Out of Scope Changes check
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Full details: Title check
Explanation
The title "Bound the direction precompute shape cache" matches the main change: DirectionPrecomputer now uses a point-budgeted LRU cache (recentShapes, capped at 500,000 points) in place of the full-table shapes map. It is short, specific, and a teammate scanning history would understand the primary change. It does not mention the removed GetAllShapes query or the singleflight reads, but it does not need to cover every detail.
Full details: Description check
Explanation
The description follows the repository template: it has the template marker, a 'Part of #1657' reference, 'What it does', 'Root cause', 'Testing' (with the failing-on-main line and manual check filled in), a checklist, and reviewer notes. The response comparison section is omitted, and the template's guidance says to delete it if no Java-served response changed, which fits this memory-focused change. The 'Fixes #' line is replaced by 'Part of #1657', which the template allows. The final checklist item ('I read every line of this diff and can explain it if asked.') is unchecked, so the author has not yet met the ready-for-review requirement. The PR should stay in Draft until that box is checked. The 'Testing' section also contains a summarized table rather than raw command output, which the template asks for, though the author notes the full log exists.
Resolution
Before marking ready for review, check the final box under Checklist ('I read every line of this diff and can explain it if asked') only if it is true. Otherwise keep the pull request as Draft. Optionally paste the actual TestImportMemory output in place of the summary table, as the template asks for real output.
Full details: Docstring Coverage
Explanation
Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 4 functions across 6 files.
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
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recentShapes lives outside the directionCache generation, so ClearCache never resets it. The only thing preventing stale shapes after a reload is this comment. Moving recentShapes and shapeLoads into directionCache, the way requestGroup and tripGroup already are, would drop the "one import only" restriction. It would also stop a reload-time read from filling the new generation, which the directionCache comment says must not happen.
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Leaving this for now. Only the calculator NewDirectionPrecomputer creates has a recentShapes, it's created fresh for each import, and nothing calls ClearCache on it. The long-lived manager.DirectionCalculator has none. So the stale-shape case can't happen today. Moving it into directionCache would mean threading the cache generation through calculateOrientationAtStop and about 15 test call sites, which is fine hardening for later but out of scope here.
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Whether the LRU hits depends on ListStops order (stop_id), not shape order, as the PR description notes. A feed whose stop IDs do not follow routes can fall back to about the no-cache time (31 s vs 21 s for NJT). A deeper fix is to give workers stops in shape order (for example, sort stops by the first shape that serves them), or to compute per shape. Then a small cache, or none, gets close to one read per shape whatever the ID scheme.
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Agreed that's the deeper fix, but handing workers stops in shape order is a redesign of the precompute loop. The PR description already names this limit, so I'd like to take it as a follow-up.
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After a changed import, the direction precomputer read every row of
the shapes table into one Go map before computing stop directions.
For NJ Transit bus that is 3.3 million points, and the map alone held
hundreds of MB. Once the import itself is fixed (#1657), this would
set the peak.
The precomputer now keeps the most recently used shapes up to 500,000
points (about 20 MB of rows), and reads others with the per-shape
query the calculator already used when no cache was set. The budget
counts points, not shapes, because shape sizes vary widely between
feeds. Lookups of one shape share a single read, and the completion
log reports cache hits and reads.
The query returns the same points in the same order (ordered by
shape_pt_sequence), so stop directions are unchanged: the RABA parity
digests, which include stops.direction, still match. On NJ Transit,
the precompute holds about 580 MiB of heap while it runs instead of
about 1.5 GiB, and the import takes as long as before (about 21 s).
Without any cache it took 31 s, because each shape was read again for
every stop on it. A feed whose stops visit shapes in a scattered
order gets fewer hits, but never more memory than the budget.
The full shape map was set only by the precomputer, so SetShapeCache
and its lock are removed; tests now seed the bounded cache instead.
GetAllShapes had no other caller and is removed.
add assumed the shape was not cached yet. A second add for the same
shape pushed a second list element and counted its points twice, and
evicting the old element later deleted the live map entry too. add
now replaces the points of a cached shape and moves it to the front.
add also used slices.Clip, which only lowers the capacity and keeps
the whole backing array alive. The query builds its result with
append, so that array can be up to twice as long as the points the
budget counts. add now copies the points with slices.Clone so the
memory kept matches the budget.
shapePoints sent every lookup through shapeLoads.Do, so each cache
hit paid for the singleflight mutex, map insert and delete, and
WaitGroup before it took the recentShapes lock. Hits are most
lookups, and the precomputer makes them from NumCPU workers at once.
shapePoints now checks recentShapes first and uses singleflight only
for misses, checking the cache again inside Do in case a read
finished between the two.
The completion log's counts also did not add up. Misses were counted
before the read, so failed reads were included, and lookups that
shared another worker's read were counted nowhere. recentShapes now
counts lookups, hits, and shapes stored after a successful read, and
the log reports shape_lookups, shape_cache_hits, and shape_reads.
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Part of #1657 (step 2d). Stacked on #1667.
What it does
DirectionPrecomputerno longer loads every row of theshapestable into one Go map before computing stop directions. It keeps the most recently used shapes up to 500,000 points (about 20 MB of rows) in a small LRU cache,recentShapes, and reads any other shape with the per-shape query the calculator already used. Concurrent lookups of one shape share one read through asingleflightgroup. The completion log reportsshape_cache_hitsandshape_reads.Removed:
SetShapeCache, its lock and "initialized" flag (only the precomputer used them), and theGetAllShapesquery (no other caller).Root cause
For NJ Transit bus the all-shapes map held 3.3 million points, and the precompute stage peaked at 1.70 GiB of heap. Once the import stops holding the whole feed (#1669, #1672, #1676), this map would be the process peak. The per-shape query returns the same points in the same order, so stop directions do not change: the RABA table digests, which include
stops.direction, are unchanged.Testing
mainbefore this change: n/a (memory change, no behavior change)TestImportMemory(Add parity and memory test tooling for the import #1662) at the stack base and at this branch:main)precomputation_batch_written)Full per-stage output is in the
TestImportMemorylog; the table shows the stages this PR moves.New tests:
TestRecentShapesEvictsLeastRecentlyUsedPoints(LRU eviction by point budget, oversized shape kept alone),TestPrecomputeReadsEachShapeOnce(four stops on one shape cause one read, with the expected directions), and a failed read is not cached.Checklist
mainand passes on this branch.gtfsdb/(db.go,models.go,query.sql.go) ortestdata/openapi.yml(synced from upstream).r.Context()to DB/service calls, notcontext.Background().testdata/openapi.yml, has an issue open on OneBusAway/sdk-config, or is outside the SDK and the description says why.Notes for reviewers
Size. 204 added, 420 removed. Most of the removal is the old all-shapes cache and its tests; the new cache and its tests are about 130 lines. Removing the old cache without the replacement would regress import time.
Trade-off. A feed whose stops visit shapes in a scattered order gets fewer cache hits and a slower precompute (up to the no-cache case, about 31 s instead of 21 s for NJ Transit). It never uses more memory than the budget. The hit/miss log shows whether any real feed needs the work grouped by shape instead.
Summary by CodeRabbit