Monthly summary for 2026-03: Stabilized Velox FlatMapColumnWriter by addressing dangling StringView keys during rehash. Implemented owned copies of string key data stored in stringKeys_, pre-reserved to maxKeyCount_, preventing dangling pointers when input batches are released. Added regression tests to reproduce and guard against the crash across rehash scenarios. Tied to commit 33d609bfe0881da75cbfc1ed5f786b2fbff84aba and PR #16800 with Differential Revision D96812892. Result: increased reliability, fewer crashes, and improved data processing stability for downstream workloads.

January 2026: Delivered Presto cardinality() optimization to skip unnecessary map/array reads when only the count is needed, reducing I/O and deserialization overhead. Implemented a conservative subfield pushdown using a new structure-only path [$], backward-compatibly disabled by default via optimizer pushdown-subfields-for-cardinality and a session property. Coordinator-side changes completed; worker-side integration to be added subsequently. Added extensive unit tests and documentation to validate correctness and performance impact. This work lowers latency and shuffle costs for analytical workloads involving cardinality on nested structures and improves overall query throughput.

Monthly summary for 2025-12 (prestodb/presto): Introduced a new query optimization to consolidate multiple approx_distinct calls on distinct expressions of the same type, implemented as the CombineApproxDistinctFunctions optimizer. This optimization uses set_agg with array operations to compute multiple distinct counts in a single pass, reducing aggregation overhead and improving latency for analytical workloads with non-integer types (e.g., strings, dates). The feature is opt-in via a new session property (optimize_multiple_approx_distinct_on_same_type) defaulting to false. Accompanied by comprehensive tests and documentation.

Monthly work summary for 2025-10 focused on feature delivery and quality improvements in prestodb/presto.

Month: 2025-07 – IBM/velox focused on improving parsing robustness for quoted identifiers. Delivered a targeted fix to the type parser lexer rules to correctly handle special characters and spaces within quoted identifiers, with regression tests added to ensure stability. This work reduces parsing errors in user workflows and downstream components relying on Velox type parsing.