Julian Reschke created SLING-13387:
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Summary: Paged query for aliases fails due to stale alias index
and shifting sling:alias values
Key: SLING-13387
URL: https://issues.apache.org/jira/browse/SLING-13387
Project: Sling
Issue Type: Bug
Components: ResourceResolver
Reporter: Julian Reschke
Assignee: Julian Reschke
(AI generated summary)
Alias resolution and querying rely heavily on the resource resolver's alias
index (Oak property/traversal index tracking {{{}sling:alias{}}}).
When executing *paged queries* for aliases across a large content tree,
pagination relies on consistent sorting or offset keys. However, if the alias
index is stale or if the underlying "first" values of multi-valued or
dynamically changing {{sling:alias}} properties shift unexpectedly between page
fetches, the pagination mechanism breaks. This results in failed queries,
missing results, or inconsistent data sets being returned.
h3. Steps to Reproduce
# Set up an environment with a significant volume of resources containing
{{sling:alias}} properties.
# Trigger a background content update or frequent creations/modifications that
actively alter {{sling:alias}} values.
# Execute a *paged query* (using limit/offset or cursor-based pagination)
targeting the alias index.
# Observe the query execution while the index is catching up or when the
sorting key ({{{}sling:alias{}}} first value) mutates between pages.
h3. Actual Behavior
* Paged queries fail with query execution exceptions, or return
truncated/duplicated results.
* The Oak index logs warnings or errors regarding traversal/staleness.
* Pagination cursors become invalid because the underlying index order shifted
mid-pagination due to changing property values.
h3. Expected Behavior
* Paged alias queries should remain resilient against minor index staleness or
handle shifting property values gracefully.
* Robust error handling or alternative fallback sorting mechanisms should
prevent total query failures when index states are inconsistent.
h3. Technical Notes / Root Cause
* *Index Staleness:* Oak async indexes take time to re-index, leading to a
window where queries return stale or shifting pointers.
* *Unstable Sorting Keys:* Multi-valued {{sling:alias}} properties or frequent
updates change the lexical "first" value used for ordering, breaking standard
offset/limit pagination assumptions.
* *Possible Mitigations:* Investigate implementing deterministic sorting
(e.g., combining with jcr:uuid or path as a secondary sort criterion) or
improving index configuration parameters for {{{}sling:alias{}}}.
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