This page documents the hard limits, default quotas, and tunable caps in pg_ripple. All GUC parameters listed here can be adjusted; see the GUC Reference for full details.
Limit Default GUC Error code
Max SPARQL result rows unlimited pg_ripple.sparql_max_rowsPT640 SPARQL overflow action truncatepg_ripple.sparql_overflow_action— Max algebra tree depth 256 pg_ripple.sparql_max_algebra_depthPT440 Max triple patterns per query 4096 pg_ripple.sparql_max_triple_patternsPT440 Max DESCRIBE CBD depth 16 pg_ripple.describe_max_depth— Fuzzy match input length 4096 chars pg_ripple.fuzzy_max_input_lengthPT0308 All-nodes predicate expansion cap 500 predicates pg_ripple.all_nodes_predicate_limit—
Limit Default GUC Error code
Export function max rows (Turtle/N-Triples/JSON-LD) unlimited pg_ripple.export_max_rowsPT642 Arrow Flight batch size 1000 rows/batch pg_ripple.arrow_batch_size—
Limit Default GUC Error code
Datalog max depth unlimited pg_ripple.datalog_max_depth— Datalog max derived facts unlimited pg_ripple.datalog_max_derived— Well-founded semantics max rounds 100 pg_ripple.wfs_max_iterationsPT520 SHACL rule max iterations 100 pg_ripple.shacl_rule_max_iterationsPT301 Lattice inference max iterations 1000 pg_ripple.lattice_max_iterationsPT540 Probabilistic Datalog max iterations 100 pg_ripple.prob_datalog_max_iterations— SHACL score log retention 30 days pg_ripple.shacl_score_log_retention_days—
Limit Default GUC Error code
Per-SERVICE timeout 30 s pg_ripple.federation_timeoutPT214 Connect timeout 10 s pg_ripple.federation_connect_timeout_secsPT214 Max rows per SERVICE call 10,000 pg_ripple.federation_max_results— Max response body per endpoint 100 MiB pg_ripple.federation_max_response_bytesPT215 Partial recovery max bytes 64 KiB pg_ripple.federation_partial_recovery_max_bytes— Circuit breaker threshold 5 failures pg_ripple.federation_circuit_breaker_thresholdPT217 Parallel SERVICE workers 4 pg_ripple.federation_parallel_max—
Limit Default GUC Error code
Max PageRank iterations 100 pg_ripple.pagerank_max_iterations— Max seed IRIs per call 1024 pg_ripple.pagerank_max_seedsPT0411 Convergence check norm L1 pg_ripple.pagerank_convergence_norm—
Limit Default GUC Notes
VP promotion threshold 1,000 triples pg_ripple.vp_promotion_thresholdBelow threshold: stored in vp_rare Merge batch size 1,000,000 rows pg_ripple.merge_batch_sizePer-merge INSERT…SELECT Merge fence lock timeout 5,000 ms pg_ripple.merge_lock_timeout_ms— CDC watermark batch size 100 events pg_ripple.cdc_watermark_batch_size— VP promotion batch size 10,000 rows pg_ripple.vp_promotion_batch_size— Bidi relay max in-flight 1,000 ops pg_ripple.bidi_relay_max_inflightDrop-oldest policy Dictionary vacuum threshold 10,000 terms pg_ripple.dict_vacuum_thresholdPost-encode auto-VACUUM
Limit Default GUC Notes
Dictionary LRU cache size 65,536 entries pg_ripple.dictionary_cache_sizeXXH3-128 hash map Shared memory budget 64 MiB pg_ripple.cache_budget_mbpostmaster-scoped
Limit Default Config Notes
Max request body size 10 MiB PG_RIPPLE_HTTP_MAX_BODY_BYTESApplies to SPARQL UPDATE body Rate limit unlimited PG_RIPPLE_HTTP_RATE_LIMITPer source IP, req/s Arrow Flight ticket expiry 3,600 s pg_ripple.arrow_flight_expiry_secsSigned HMAC tickets Connection pool size 16 PG_RIPPLE_HTTP_POOL_SIZEPostgres connections
Limit Default GUC Notes
Event audit retention 90 days pg_ripple.audit_retention_days_pg_ripple.event_auditSHACL score log retention 30 days pg_ripple.shacl_score_log_retention_days_pg_ripple.shacl_score_logCDC slot idle timeout 3,600 s pg_ripple.cdc_slot_idle_timeout_secondsOrphan slot cleanup VACUUM dict batch size 200 entries pg_ripple.vacuum_dict_batch_sizevacuum_dictionary()
These limits are baked into the implementation:
Constraint Value Notes
Dictionary hash space 2^64 (XXH3-128) Collision probability negligible in practice Maximum SID (statement ID) 2^63 − 1 (i64) PostgreSQL sequence maximum Maximum named graph ID 2^63 − 1 (i64) Same sequence namespace Maximum predicate ID 2^63 − 1 (i64) Same sequence namespace SPARQL 1.1 spec compliance Full SELECT, CONSTRUCT, DESCRIBE, ASK, UPDATE, LOAD, CLEAR, DROP, ADD, MOVE, COPY PostgreSQL target 18.x only pgrx 0.18, no older PG support
For a 100 GB RDF dataset on a 32-core / 128 GB RAM server:
# postgresql.conf overrides
pg_ripple.dictionary_cache_size = 1000000
pg_ripple.cache_budget_mb = 512
pg_ripple.sparql_max_rows = 100000
pg_ripple.export_max_rows = 500000
pg_ripple.merge_threshold = 50000
pg_ripple.merge_workers = 4
pg_ripple.datalog_parallel_workers = 8
pg_ripple.federation_timeout = 60
pg_ripple.federation_parallel_max = 8
pg_ripple.pagerank_max_iterations = 200
See Performance Tuning for a full tuning guide.