perf: skip org unit/period resolution in dimension recommendations

[jason-p-pickering]

Summary

Fixes https://dhis2.atlassian.net/browse/DHIS2-21671

/api/dimensions/recommendations resolved every dimension on the request via
DataQueryService.getFromRequest, including ou:LEVEL-*. On a large hierarchy this hydrates all org
units at that level as full Hibernate entities and sorts them — ~4.5s CPU and ~3.2 GB allocated in
production profiling (Nigeria EMIS) — yet the result is discarded: getRecommendedDimensions
only reads the data (dx) dimension's data elements / program indicators (plus org unit group sets
loaded separately). The org unit and period dimensions are never read.

This PR scopes the request to the dx dimension before resolving it, so getFromRequest never
resolves/hydrates the unused dimensions.

Profiling (before)

Metric	Value
Duration	4,487 ms
CPU	4,480 ms
Allocated memory	3.2 GB
DB time	~5 ms (not DB-bound)
Response	304

Flame graph hot path: getFromRequest → getOrgUnitDimension →
getOrganisationUnitsAtLevels → HibernateOrganisationUnitStore.getOrganisationUnits
(full-entity hydration) → ComparableTimSort/Collections.sort.

Change

Set<String> dataDimensionsOnly =
    request.getDimension() == null ? null
        : request.getDimension().stream()
            .filter(param -> DATA_X_DIM_ID.equals(getDimensionFromParam(param)))
            .collect(Collectors.toSet());

DataQueryParams params =
    dataQueryService.getFromRequest(
        DataQueryRequest.newBuilder().dimension(dataDimensionsOnly).build());

The sole caller (DimensionController) sets only the dimension param, so this is
behaviour-equivalent for everything the endpoint consumes. No change to DataQueryService,
getOrganisationUnitsAtLevels, or HibernateOrganisationUnitStore — zero blast radius on other callers.

Tests

New unit test DefaultAnalyticsDimensionServiceTest.getRecommendedDimensionsResolvesOnlyDataDimension
captures the DataQueryRequest passed to getFromRequest and asserts only the dx param survives
(ou / pe stripped). Verified failing before the fix, passing after.

Notes

• Same large-hierarchy org-unit hydration pattern seen in geoFeatures / dataSets-no-fields /
  getMetaData OUG-count issues — but here the work is pure dead work, not a needed result.
• JIRA ticket writeup to be filed; this is a self-contained server-side fix.

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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