Scan Metrics

DeltaScanMetrics is a live, cloneable handle for one scan. Calling snapshot returns an immutable point-in-time DeltaScanMetricsSnapshot. The handle stays usable after its batch stream finishes or is dropped.

Core scan metrics

Field	Meaning
`snapshot_version`	Delta snapshot version used by the scan.
`parquet_backend`	Backend selected to read Parquet data files.
`scan_partitions_planned`	Final number of execution partitions, including DataFusion repartitioning.
`files_planned`	Physical data files selected during initial whole-file planning.
`add_actions_excluded_during_planning`	Best-effort count of Add actions excluded during metadata planning, when known.
`estimated_input_rows`	Estimated rows in selected input files before row predicates and deletion vectors, when every file supplied a valid estimate.
`estimated_input_bytes`	Estimated bytes in selected input files when every file supplied a size.
`scan_partitions_started`	Execution partitions that started.
`scan_partitions_completed`	Execution partitions that reached normal completion.
`file_tasks_started`	Whole-file or ranged tasks that started.
`file_tasks_completed`	Whole-file or ranged tasks that reached normal completion.
`scheduler_batches_emitted`	Batches emitted by the scheduler before final stream filtering, projection, and limits.
`scheduler_rows_emitted`	Rows emitted by the scheduler before final stream filtering, projection, and limits.
`deletion_vector_payloads_loaded`	Deletion-vector payloads loaded.
`deletion_vectors_applied`	Deletion-vector masks applied.
`deletion_vector_rows_deleted`	Rows removed by those masks.
`deletion_vector_failures`	Deletion-vector read or masking failures.
`deletion_vector_coordinate_rejections`	Deletion-vector coordinate operations rejected by safety checks.
`parquet_data_file_exact_ranges_requested`	Normalized, non-overlapping exact ranges requested through Direct Parquet multi-range calls.
`parquet_data_file_exact_range_bytes_requested`	Bytes covered by those normalized exact ranges.
`parquet_data_file_physical_range_requests_planned`	Physical range requests selected by the automatic planner. Store-delegated calls do not contribute because their physical plan is not visible.
`parquet_data_file_physical_range_bytes_planned`	Bytes covered by the automatically planned physical requests.
`parquet_data_file_cold_start_range_plans`	Automatic plans selected without a usable transport estimate. Safety bounds may still merge a large exact plan.
`parquet_data_file_cost_based_exact_range_plans`	Automatic plans where a usable estimate favored the normalized minimum-byte ranges.
`parquet_data_file_cost_based_merged_range_plans`	Automatic plans where a usable estimate favored including gaps to reduce physical requests.
`parquet_data_file_store_delegated_range_plans`	Range-planning decisions passed to the store's own multi-range implementation.
`parquet_data_file_range_get_operations`	Ranged operations observed by the Direct Parquet wrapper. A forwarded store-provided multi-range call counts once.
`parquet_data_file_full_get_operations`	Direct Parquet data-file GET operations without a range.
`parquet_data_file_bytes_received`	Bytes delivered successfully through the `Direct` backend's object-store boundary.
`estimated_parquet_task_bytes_admitted`	Estimated bytes admitted across `Direct` backend tasks. A ranged task contributes its range length.

add_actions_excluded_during_planning is not an exact active-file count. Delta Kernel's final selection also reconciles Add and Remove actions.

The Parquet I/O and range-planning fields are Some, including Some(0), for Direct. They are None for DeltaKernel because its object-store calls happen behind the Kernel reader boundary.

DataFusion metrics

datafusion::ScanMetricsSnapshot contains the core scan snapshot above and adds provider-specific fields.

Field	Meaning
`reader_metrics`	`DeltaScanMetricsSnapshot` for this physical scan.
`uses_arrow_view_types`	Whether the provider requested Arrow view arrays for string and binary data columns.
`configured_batch_size_rows`	DataFusion's configured batch row target, recorded when execution starts.
`dynamic_partition_tasks_pruned`	Whole-file or ranged tasks skipped by a dynamic partition filter before admission.
`dynamic_partition_tasks_kept`	Tasks kept after consulting dynamic partition filters.
`dynamic_filters_received`	Physical filters offered after optimization.
`dynamic_filters_accepted`	Offered filters retained for partition pruning.
`dynamic_filters_rejected`	Offered filters rejected by the dynamic-filter policy.
`dynamic_partition_filter_checks`	Dynamic partition filters checked against file tasks during admission.
`dynamic_partition_tasks_kept_unusable_metadata`	Tasks kept because partition metadata was missing, invalid, or could not be parsed.
`dynamic_partition_tasks_kept_unevaluable_filter`	Tasks kept because a dynamic filter was unavailable or could not be evaluated.

datafusion::collect_scan_metrics walks a physical plan in depth-first order and returns each distinct Delta scan metric handle once.

Parquet I/O boundaries

The I/O counters observe calls made through the Direct backend's data-file object_store wrapper. They are useful for comparing scan choices, but they are not network billing counters.

Range and full GET counters advance immediately before an operation is passed to the underlying store, so failed operations still count. A forwarded store-provided multi-range call counts once because the wrapper cannot see how the store performs that call.
Requested range counts and bytes describe the normalized minimum-byte plan. Planned request counts and bytes describe the physical plan selected for built-in remote stores. These counters advance before the physical reads start, so they also include plans whose reads later fail.
Exactly one decision counter advances for each non-empty multi-range call. Automatic calls count as cold start, cost-based exact, or cost-based merged. Calls that use the store's own multi-range implementation count as store-delegated; their internal physical request count and planned bytes are not observable here.
For automatic plans with requested bytes, aggregate byte amplification is parquet_data_file_physical_range_bytes_planned divided by parquet_data_file_exact_range_bytes_requested. Calculate the ratio from the aggregate counters rather than averaging ratios from individual calls.
Received bytes count successful response chunks delivered through the wrapper. Merged reads can include unrequested gaps. A store-provided multi-range call reports the bytes returned to Parquet; any extra work inside the store is not visible.
Admitted task bytes add the estimated span of each task. A whole-file task contributes its file size, while a ranged task contributes its range length.

The wrapper cannot see lower-level HTTP retries, wire compression, provider billing units, or object-store work hidden behind DeltaKernel. A local file read may also begin before a result is delivered through the wrapper, so a failed or dropped local result can leave the received-byte counter at zero.