> ## Documentation Index > Fetch the complete documentation index at: https://www.paradedb.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Configuration Reference > Runtime settings for ParadeDB and pg_search ParadeDB exposes runtime configuration through Postgres settings, also known as GUCs. Most settings can be changed per session: ```sql theme={null} SHOW paradedb.enable_custom_scan; SET paradedb.enable_custom_scan = off; RESET paradedb.enable_custom_scan; ``` For persistent configuration, use normal Postgres mechanisms such as `ALTER DATABASE`, `ALTER ROLE`, or `ALTER SYSTEM`. ```sql theme={null} ALTER DATABASE app SET paradedb.max_topk_chunk_size = 200000; ALTER ROLE app_user SET paradedb.vector_cluster_max_probe = 0.05; ``` Planner and execution settings can change query plans, memory use, latency, or recall. Change them deliberately and prefer session-level `SET` while testing. ## Query Planning These settings control whether ParadeDB proposes custom plans for eligible queries. | Setting | Default | Context | Description | | ---------------------------------------------- | ------------- | ------- | --------------------------------------------------------------------------------------------------- | | `paradedb.enable_custom_scan` | `on` | user | Enables ParadeDB's base custom scan, which replaces table scans with ParadeDB index scans. | | `paradedb.enable_aggregate_custom_scan` | `on` | user | Enables the aggregate custom scan for eligible `pdb.agg` and `GROUP BY` queries. | | `paradedb.enable_join_custom_scan` | `on` | user | Enables the join custom scan, which pushes eligible joins into the ParadeDB executor. | | `paradedb.enable_custom_scan_without_operator` | `off` | user | Allows custom scans without a ParadeDB search operator when the whole `WHERE` clause can push down. | | `paradedb.enable_filter_pushdown` | `on` | user | Allows non-indexed predicates to use heap filtering after the ParadeDB scan. | | `paradedb.enable_range_partitioned_join` | `off` | user | Enables range co-partitioned joins for indexes configured with `partition_by`. | | `paradedb.enable_heuristic_selectivity` | `on` | user | Uses cheap planner selectivity estimates for expensive fuzzy, regex, and range query shapes. | | `paradedb.per_tuple_cost` | `100000000.0` | user | Planner cost multiplier that discourages using ParadeDB operators outside a supported index plan. | | `paradedb.explain_recursive_estimates` | `off` | user | Shows recursive document-count estimates in `EXPLAIN VERBOSE`; intended for debugging. | ## Top K These settings affect queries that combine a ParadeDB predicate with `ORDER BY ... LIMIT`. See [Top K](/docs/reference/full-text/top-k). | Setting | Default | Context | Description | | -------------------------------------- | -------- | ------- | -------------------------------------------------------------------------------------------- | | `paradedb.limit_fetch_multiplier` | `1.0` | user | Multiplies the query `LIMIT` to choose the initial Top K fetch size. | | `paradedb.topk_retry_scale_factor` | `2` | user | Multiplies the fetch size on retries when the first Top K pass does not collect enough rows. | | `paradedb.max_topk_chunk_size` | `100000` | user | Maximum chunk size for Top K collection. | | `paradedb.check_topk_scan` | `on` | user | Logs a warning when a `LIMIT` query expected to use Top K cannot use it. | | `paradedb.enable_segmented_topk` | `on` | user | Enables segmented Top K pruning for late-materialized string and byte columns. | | `paradedb.expensive_query_cost_factor` | `25.0` | user | Scales planner cost estimates for fuzzy, regex, and more-like-this queries. | ## Aggregates These settings affect `pdb.agg`, `GROUP BY`, and faceted search. See [Aggregate Syntax](/docs/reference/aggregates/overview). | Setting | Default | Context | Description | | ---------------------------------------------- | --------- | ------- | ----------------------------------------------------------------------------------------- | | `paradedb.max_term_agg_buckets` | `65000` | user | Maximum number of terms aggregation buckets or groups before ParadeDB errors. | | `paradedb.max_window_aggregate_response_bytes` | `1048576` | user | Maximum serialized response size for a window aggregate during a parallel scan, in bytes. | | `paradedb.check_aggregate_scan` | `on` | user | Logs a warning when a query expected to use aggregate scan cannot use it. | | `paradedb.add_doc_count_to_aggs` | `off` | user | Internal testing setting for aggregate null-handling compatibility. | ## Vector Search These settings affect vector queries over `pgvector`'s `vector` type. See [Indexing Vectors](/docs/reference/indexing/indexing-vectors) and [Tuning Recall and Latency](/docs/reference/vector/tuning). | Setting | Default | Context | Description | | --------------------------------------- | --------------- | ------- | -------------------------------------------------------------------------------------------- | | `paradedb.vector_cluster_max_probe` | `0.02` | user | Maximum fraction of each segment's vector clusters that a vector `ORDER BY` query may probe. | | `paradedb.vector_clustering_threshold` | `500` | user | Segment document-count threshold at which merged vector storage switches from flat to IVF. | | `paradedb.vector_fixed_probe_cost_rows` | Tantivy default | user | Fixed per-probe cost used by the IVF probe-budget model; mainly for testing and calibration. | ## Parallel Execution These settings control ParadeDB's parallel execution and MPP paths. | Setting | Default | Context | Description | | ----------------------------------- | -------- | ------- | ----------------------------------------------------------------------------------------------------- | | `paradedb.min_rows_per_worker` | `300000` | user | Minimum estimated rows per parallel worker. Set to `0` to use segment-based parallelism only. | | `paradedb.mpp_min_rows` | `500000` | user | Minimum estimated source row count before MPP execution can engage. Set to `0` to disable the gate. | | `paradedb.mpp_queue_size` | `8MB` | user | Per-inbox ring size for MPP shuffles. Accepts Postgres byte units. | | `paradedb.mpp_request_timeout` | `300s` | user | Maximum time an MPP worker fragment waits for another partition request. Set to `0` to disable. | | `paradedb.mpp_debug` | `off` | user | Emits verbose MPP runtime diagnostics to the Postgres server log. | | `paradedb.mpp_trace` | `off` | user | Emits MPP setup timing diagnostics to the Postgres server log. | | `paradedb.mpp_test_panic_in_worker` | `off` | user | Debug-build testing hook that intentionally panics in an MPP worker. Not available in release builds. | ## Columnar Execution These settings control how ParadeDB reads columnar data from the index. | Setting | Default | Context | Description | | ----------------------------------------- | ------- | ------- | -------------------------------------------------------------------------------------------------------- | | `paradedb.enable_fast_field_exec` | `on` | user | Enables optimized columnar executors for narrow projections. | | `paradedb.enable_columnar_exec` | `on` | user | Enables the columnar executor for multi-column string and numeric projections. | | `paradedb.columnar_exec_column_threshold` | `3` | user | Number of projected index columns below which the columnar executor is used instead of normal row fetch. | ## Term Set Pushdown These settings affect pushed-down `IN`, `ANY`, and term-set queries. | Setting | Default | Context | Description | | -------------------------------------------------------- | ---------- | ------- | -------------------------------------------------------------------------------------------------- | | `paradedb.hash_join_inlist_pushdown_max_size` | `16777216` | user | Maximum byte size of an `IN` list that can be pushed down to a `TermSet` query. | | `paradedb.hash_join_inlist_pushdown_max_distinct_values` | `20000` | user | Maximum number of distinct values in a pushed-down `IN` list. Set to `0` to disable this pushdown. | | `paradedb.term_set_gallop_enabled` | `on` | user | Enables galloping execution for term-set queries on sorted columnar segments. | | `paradedb.term_set_bitset_max_density_unique` | `0.0005` | user | Density threshold for selecting bitset execution on unique-valued columns. | | `paradedb.term_set_bitset_max_density_multi` | `0.005` | user | Density threshold for selecting bitset execution on columns where multiple rows share a value. | | `paradedb.dynamic_filter_batch_size` | `0` | user | Caps scanner batch size during dynamic filter pushdown. `0` uses the scanner default. | ## Index Maintenance These settings affect segment layout and background merging. | Setting | Default | Context | Description | | ------------------------------------------- | ------- | ------- | ------------------------------------------------------------------------------------- | | `paradedb.global_target_segment_count` | `0` | sighup | Overrides every index's `target_segment_count` when non-zero. Requires config reload. | | `paradedb.global_enable_background_merging` | `on` | sighup | Enables background segment merging globally. Requires config reload. | | `paradedb.global_mutable_segment_rows` | `-1` | user | Overrides every index's `mutable_segment_rows` when set to a non-negative value. | ## Related Postgres Settings ParadeDB also relies on standard Postgres memory settings: | Setting | Used for | | ---------------------- | -------------------------------------------------------------------------------- | | `maintenance_work_mem` | Index builds and index maintenance. Each parallel worker needs at least 15MB. | | `work_mem` | Query execution memory; ParadeDB clamps the effective Tantivy budget internally. |