Architecture Overview ===================== This page gives a bird's-eye view of ProvSQL's internals: how the extension is loaded, how its components are organized, and how data flows from an SQL query to a provenance evaluation result. For a detailed walkthrough of the query rewriting pipeline, see :doc:`query-rewriting`. Extension Lifecycle ------------------- ProvSQL is a PostgreSQL *shared-library extension*. Because it installs a **planner hook**, the library must be loaded at server start via the ``shared_preload_libraries`` configuration variable; it cannot be loaded on demand. When PostgreSQL starts, it calls :cfunc:`_PG_init`, which: 1. Registers the GUC (Grand Unified Configuration) variables; the most central are: - ``provsql.active`` -- enable/disable provenance tracking (default: on). - ``provsql.provenance`` -- the provenance class: 'where' / 'semiring' (default) / 'absorptive' / 'boolean'. - ``provsql.update_provenance`` -- track provenance through DML statements (default: off). - ``provsql.verbose_level`` -- verbosity for debug messages (0--100, default: 0). - ``provsql.aggtoken_text_as_uuid`` -- when on, ``agg_token_out`` emits the underlying provenance UUID instead of the default ``"value (*)"`` display string (default: off). - ``provsql.tool_search_path`` -- colon-separated directories prepended to ``PATH`` when invoking external tools (d4, c2d, minic2d, dsharp, weightmc, graph-easy); see :cfile:`external_tool.cpp`. Further GUCs gate individual routes and optimizations (``provsql.joint_width``, ``provsql.mobius``, ``provsql.simplify_on_load``, ...); grep :cfile:`provsql.c` for ``DefineCustom`` for the full list, and see :doc:`/user/configuration` for the user-facing reference. 2. Installs the **planner hook** (:cfunc:`provsql_planner`) by saving the previous hook in ``prev_planner`` and replacing ``planner_hook``. 3. Installs the **ProcessUtility hook** (:cfunc:`provsql_ProcessUtility`) by saving the previous hook in ``prev_ProcessUtility``. Used by the CTAS / ``SELECT INTO`` / matview lineage propagation path (see :ref:`tid-bid-propagation`). 4. Installs **shared-memory hooks** for inter-process coordination (see :doc:`memory`). 5. Installs **executor hooks** (``ExecutorStart`` / ``ExecutorEnd``) that maintain a nesting depth counter so the :cfunc:`provsql_classify_query` NOTICE fires only on the user's outermost statement (the rewriter's PL/pgSQL helpers replan internally, which would otherwise produce spurious extra NOTICEs). 6. Launches the **mmap background worker** that manages persistent circuit storage. When the server shuts down, :cfunc:`_PG_fini` restores the previous planner, ``ProcessUtility``, executor, and shared-memory hooks. Component Map ------------- ProvSQL is a mixed C/|cpp| codebase. The PostgreSQL interface layer is written in C (required by the extension API); complex data structures and algorithms are in |cpp|. **C files** (PostgreSQL interface layer): *Planner hook and query rewriting* - :cfile:`provsql.c` -- planner hook, ProcessUtility hook (CTAS / ``SELECT INTO`` / matview lineage), executor hooks, and the bulk of the query rewriting logic (~15,000 lines). - :cfile:`safe_query.c` / :cfile:`safe_query.h` -- safe-query rewriter for hierarchical CQs (Dalvi & Suciu 2012), gated on the ``'boolean'`` provenance class ; includes the FD-aware extensions (constant-selection elimination, PK FDs, deterministic-relation transparency, PK-unifiable / disjoint-constant self-joins) and the propagation normalisation pre-passes (``INNER`` / ``CROSS`` JoinExpr flattening, simple-subquery inlining). See :ref:`safe-query-rewriter`. - :cfile:`classify_query.c` / :cfile:`classify_query.h` -- query-time TID / BID / OPAQUE classifier exposed through the ``provsql.classify_top_level`` GUC. - :cfile:`qual_classify.c` / :cfile:`qual_classify.h` -- shared predicate-tree helpers (AND flattening, equijoin / constant-selection recognition, per-relation qual splitting) consumed by both the safe-query rewriter and the joint-width recogniser. - :cfile:`joint_width_query.c` -- planner-time recogniser for the joint-width and Möbius UCQ routes (descriptor extraction, transparent ``ucq_joint_provenance`` / ``ucq_mobius_provenance`` substitution). *Utilities and shared state* - :cfile:`provsql_utils.c` / :cfile:`provsql_utils.h` -- OID cache (:cfunc:`get_constants`), type helpers, gate-type enum. - :cfile:`provsql_error.h` -- ``provsql_error`` / ``_warning`` / ``_notice`` / ``_log`` macros. - :cfile:`c_cpp_compatibility.h` -- small shims for mixing C and C++ sources. *Memory-mapped circuit store* - :cfile:`provsql_mmap.c` / :cfile:`provsql_mmap.h` -- background worker and IPC primitives. - :cfile:`provsql_shmem.c` / :cfile:`provsql_shmem.h` -- shared-memory segment setup. *SQL-callable functions* - :cfile:`provenance.c` -- error stub for the :sqlfunc:`provenance` SQL function (reached only when a query bypasses the planner hook). - :cfile:`provenance_evaluate.c` -- SQL-level semiring evaluation (user-defined ``plus``/``times``/... functions). - :cfile:`agg_token.c` / :cfile:`agg_token.h` -- the ``agg_token`` composite type (UUID + running value). *PostgreSQL version compatibility* - :cfile:`compatibility.c` / :cfile:`compatibility.h` -- shims for cross-version PostgreSQL API differences. **C++ files** (data structures and algorithms): *Circuit representation* - :cfile:`Circuit.h` / :cfile:`Circuit.hpp` -- template base class parameterised by gate type; inherited by all circuit variants. - :cfile:`GenericCircuit.h` / :cfile:`GenericCircuit.hpp` / :cfile:`GenericCircuit.cpp` -- semiring-agnostic in-memory circuit. - :cfile:`BooleanCircuit.h` / :cfile:`BooleanCircuit.cpp` -- Boolean circuit used for knowledge compilation and probability evaluation. - :cfile:`WhereCircuit.h` / :cfile:`WhereCircuit.cpp` -- where-provenance circuit. - :cfile:`DotCircuit.h` / :cfile:`DotCircuit.cpp` -- GraphViz DOT export of circuits. *Persistent storage and in-memory reconstruction* - :cfile:`MMappedCircuit.h` / :cfile:`MMappedCircuit.cpp` -- mmap-backed persistent circuit store. - :cfile:`CircuitFromMMap.h` / :cfile:`CircuitFromMMap.cpp` -- reads the mmap store to build in-memory :cfunc:`GenericCircuit` / :cfunc:`BooleanCircuit` instances. - :cfile:`CircuitCache.h` / :cfile:`CircuitCache.cpp` / :cfile:`circuit_cache.h` -- per-session gate cache. - :cfile:`MMappedUUIDHashTable.h` / :cfile:`MMappedUUIDHashTable.cpp` -- open-addressing hash table keyed by UUID, stored in mmap. - :cfile:`MMappedVector.h` / :cfile:`MMappedVector.hpp` -- ``std::vector``-like container over an mmap region. - :cfile:`MMappedTableInfo.h` -- the per-relation :cfunc:`ProvenanceTableInfo` record (TID / BID / OPAQUE kind, multi-column BID block-key, base-ancestor set) ; see :ref:`per-table-metadata`. *Semiring evaluation* - ``semiring/*.h`` -- header-only semiring implementations (Boolean, BoolExpr, Counting, Formula, How, IntervalUnion, Lukasiewicz, MinMax, Tropical, Viterbi, Which, Why). - :cfile:`provenance_evaluate_compiled.cpp` / :cfile:`provenance_evaluate_compiled.hpp` -- dispatcher for compiled semirings. - :cfile:`having_semantics.cpp` / :cfile:`having_semantics.hpp` -- pre-evaluation of ``HAVING`` sub-circuits before the main semiring traversal. *Aggregation* - :cfile:`Aggregation.h` / :cfile:`Aggregation.cpp` -- aggregate operator enum, accumulator interface, and built-in accumulators (see :doc:`aggregation`). - :cfile:`aggregation_evaluate.c` -- SQL entry points for aggregate-provenance evaluation. *Continuous random variables* (see :doc:`continuous-distributions`) - :cfile:`RandomVariable.h` / :cfile:`RandomVariable.cpp` / :cfile:`random_variable_type.c` -- the ``random_variable`` type, the ``DistributionSpec`` POD, and the ``gate_rv`` blob parser. - ``distributions/`` -- the registry-driven per-family ``Distribution`` class hierarchy (one self-registering file per family). - :cfile:`MonteCarloSampler.h` / :cfile:`MonteCarloSampler.cpp` -- the Monte Carlo sampler. - :cfile:`RangeCheck.h` / :cfile:`RangeCheck.cpp` -- support-interval propagation and comparator resolution. - :cfile:`AnalyticEvaluator.h` / :cfile:`AnalyticEvaluator.cpp` -- closed-form CDF resolution for ``gate_cmp``. - :cfile:`Expectation.h` / :cfile:`Expectation.cpp` -- analytical moment evaluator (with :cfile:`PivotIntegration.h`, the shared quadrature core). - :cfile:`HybridEvaluator.h` / :cfile:`HybridEvaluator.cpp` -- peephole simplifier and island decomposition. - :cfile:`InformationTheory.h` / :cfile:`InformationTheory.cpp` -- entropy / KL / mutual-information readouts. *External tools and KCMCP* (see :doc:`kc-server-protocol`) - :cfile:`external_tool.cpp` -- external-tool resolution and invocation (``provsql.tool_search_path``, process groups). - :cfile:`ToolRegistry.cpp` -- the compiled-in seed of the ``provsql.tools`` registry. - :cfile:`kcmcp_protocol.h` / :cfile:`kcmcp_protocol.cpp` -- shared KCMCP wire codec. - :cfile:`kcmcp_client.cpp` -- in-extension KCMCP client. - :cfile:`kcmcp_supervisor.c` -- background worker supervising the managed KCMCP server. - :cfile:`kcmcp_server.cpp` / :cfile:`dimacs_cnf.cpp` -- the ``tdkc --kcmcp`` reference server. *Build-configuration and storage abstraction* - :cfile:`provsql_config.h` -- the ``PROVSQL_INPROCESS_STORE`` / ``PROVSQL_NO_SUBPROCESS`` switches for the WASM / in-process build (see :doc:`playground`). - :cfile:`MappedRegion.h` -- backing abstraction for the mmap regions (kernel-shared mmap vs. heap buffer). *Data-decomposition compilers (reachability, joint-width, Möbius)* - :cfile:`ReachabilityCompiler.cpp` / :cfile:`reachability_evaluate.cpp` -- bounded-treewidth reachability compiler (single-target, all-targets, bounded-hop, any-reach, k-terminal DPs) and its columnar SQL entry points. - :cfile:`UCQJointCompiler.cpp` / :cfile:`JointEncoding.cpp` / :cfile:`ucq_joint_evaluate.cpp` -- joint-width UCQ compiler (encoding, merged data+circuit DP, per-answer single sweep) and its materialisation entry points. - :cfile:`mobius_evaluate.cpp` -- Möbius-inversion compiler for safe UCQs (CNF lattice, lifted-inference recursion, ``gate_mobius`` construction). - :cfile:`CertifiedDDMaterialize.cpp` -- shared content-addressed materialisation of certified d-D circuits into the mmap store. *Probability, Shapley, knowledge compilation* - :cfile:`probability_evaluate.cpp` -- probability-method dispatcher (see :doc:`probability-evaluation`). - :cfile:`dDNNF.h` / :cfile:`dDNNF.cpp` -- d-DNNF data structure and linear-time probability evaluation. - :cfile:`StructuredDNNF.h` / :cfile:`StructuredDNNF.cpp` -- vtree-structured DNNF used by the inversion-free OBDD route. - :cfile:`dDNNFTreeDecompositionBuilder.h` / :cfile:`dDNNFTreeDecompositionBuilder.cpp` -- constructs a d-DNNF from a tree decomposition. - :cfile:`TreeDecomposition.h` / :cfile:`TreeDecomposition.cpp` -- tree decomposition via min-fill elimination. - :cfile:`TreeDecompositionKnowledgeCompiler.cpp` -- the standalone ``tdkc`` binary built by ``make tdkc``. - :cfile:`provsql_migrate_mmap.cpp` -- the standalone ``provsql_migrate_mmap`` binary built by ``make provsql_migrate_mmap`` (migrates pre-1.3.0 flat mmap files to the per-database layout). - :cfile:`shapley.cpp` -- Shapley and Banzhaf value computation. *Export and visualization* - :cfile:`view_circuit.cpp` -- SQL :sqlfunc:`view_circuit` function (renders a DOT graph via ``graph-easy``). - :cfile:`to_prov.cpp` -- PROV-XML export. - :cfile:`where_provenance.cpp` -- SQL where-provenance output function. *C++ utilities* - :cfile:`provsql_utils_cpp.h` / :cfile:`provsql_utils_cpp.cpp` -- C++ counterparts to :cfile:`provsql_utils.h`, including UUID string conversion. - :cfile:`subset.cpp` / :cfile:`subset.hpp` -- subset enumeration used by HAVING evaluation. - :cfile:`Graph.h` -- lightweight graph helpers used by the tree decomposition code. - :cfile:`PermutationStrategy.h` -- pluggable vertex-ordering heuristic for tree decomposition. - :cfile:`flat_map.hpp` / :cfile:`flat_set.hpp` -- contiguous associative containers used inside hot loops. Data Flow --------- The end-to-end flow of a query through ProvSQL: .. graphviz:: digraph dataflow { rankdir=LR; node [shape=box, fontname="sans-serif", fontsize=11]; edge [fontsize=9, fontname="sans-serif"]; sql [label="SQL query", shape=ellipse]; planner [label="provsql_planner"]; rewrite [label="process_query\n(rewriting)"]; exec [label="PostgreSQL\nexecutor"]; circuit [label="Circuit\n(mmap storage)"]; eval [label="Semiring\nevaluation"]; result [label="Query result\n+ provenance", shape=ellipse]; sql -> planner [label="Query tree"]; planner -> rewrite [label="has provenance?"]; rewrite -> exec [label="rewritten query"]; exec -> circuit [label="UUID tokens\n(gate creation)"]; exec -> result [label="tuples + UUIDs"]; circuit -> eval [label="circuit DAG"]; eval -> result [label="semiring values\nor probabilities"]; } 1. The user submits an SQL query. PostgreSQL parses it into a ``Query`` tree and calls the planner. 2. :cfunc:`provsql_planner` intercepts the call. If the query touches provenance-tracked tables (detected by :cfunc:`has_provenance`), it calls :cfunc:`process_query` to rewrite it. 3. The rewritten query carries an extra UUID expression in its target list. When the executor evaluates the query, it calls ProvSQL's SQL-level functions (``provenance_times``, ``provenance_plus``, etc.) to construct circuit gates. These calls route through the mmap worker to persist the circuit. 4. Each result tuple comes back with a UUID identifying the root gate of its provenance sub-circuit. 5. To *evaluate* provenance, the user calls functions like :sqlfunc:`provenance_evaluate`, :sqlfunc:`probability_evaluate`, or a compiled semiring evaluator (e.g., :sqlfunc:`sr_boolean`). These retrieve the circuit from mmap, build an in-memory :cfunc:`GenericCircuit` or :cfunc:`BooleanCircuit`, and traverse the DAG applying semiring operations. The OID Cache: ``constants_t`` ------------------------------ PostgreSQL identifies types, functions, and operators by their Object Identifiers (OIDs). ProvSQL needs to reference its own types and functions when constructing rewritten query trees, so it caches their OIDs in a :cfunc:`constants_t` structure. Key fields: - **Type OIDs**: ``OID_TYPE_UUID``, ``OID_TYPE_AGG_TOKEN``, ``OID_TYPE_GATE_TYPE``, and standard types (``BOOL``, ``INT``, ``FLOAT``, ``VARCHAR``). - **Function OIDs**: ``OID_FUNCTION_PROVENANCE_PLUS``, ``OID_FUNCTION_PROVENANCE_TIMES``, ``OID_FUNCTION_PROVENANCE_MONUS``, ``OID_FUNCTION_PROVENANCE_DELTA``, ``OID_FUNCTION_PROVENANCE_AGGREGATE``, ``OID_FUNCTION_PROVENANCE_SEMIMOD``, etc. - **Gate-type mapping**: ``GATE_TYPE_TO_OID[nb_gate_types]`` maps each :cfunc:`gate_type` enum value to the OID of the corresponding ``provenance_gate`` enum member in PostgreSQL. - **Status flag**: ``ok`` is ``true`` if the OIDs were loaded successfully (``false`` if the extension is not installed in the current database). The cache is populated by :cfunc:`get_constants`, which looks up OIDs in the system catalogs on first call and stores them per-database. Subsequent calls return the cached values without catalog access. Gate Types ---------- The provenance circuit is a directed acyclic graph (DAG) whose nodes are *gates*. Each gate has a type from the :cfunc:`gate_type` enum defined in :cfile:`provsql_utils.h`: .. list-table:: :header-rows: 1 :widths: 20 80 * - Gate type - Meaning * - ``gate_input`` - Leaf gate representing a base-table tuple. * - ``gate_plus`` - Semiring addition (⊕): duplicate elimination, UNION. * - ``gate_times`` - Semiring multiplication (⊗): joins, cross products. * - ``gate_monus`` - M-semiring monus (⊖): EXCEPT. * - ``gate_project`` - Projection gate (where-provenance). * - ``gate_eq`` - Equijoin gate (where-provenance). * - ``gate_zero`` - Semiring additive identity (0). * - ``gate_one`` - Semiring multiplicative identity (1). * - ``gate_agg`` - Aggregation operator. * - ``gate_semimod`` - Semimodule scalar multiplication (for aggregation). * - ``gate_delta`` - Delta operator (δ-semiring). * - ``gate_value`` - Scalar constant value. The ``extra`` blob encodes the literal in text form; the mode used in HAVING sub-circuits is parsed as a string by ``extract_constant_string`` (:cfile:`having_semantics.cpp`) and the *float8* mode, used to lift numeric constants into the continuous random-variable surface, is parsed as a double by the RV evaluators. * - ``gate_mulinput`` - Multivalued input (for Boolean probability). * - ``gate_cmp`` - Comparison gate (``<``, ``=``, etc.) used in HAVING sub-circuits and by the planner lift of WHERE comparisons on ``random_variable`` columns. * - ``gate_update`` - Update-provenance gate. * - ``gate_rv`` - Continuous random-variable leaf. The ``extra`` blob encodes the distribution family and parameters (e.g. ``normal:μ,σ``, ``uniform:a,b``, ``exponential:λ``); the family token resolves through the distribution registry (one self-registering file per family under ``src/distributions/``, see :doc:`continuous-distributions`). * - ``gate_arith`` - ``N``-ary arithmetic over scalar children. The operator tag (``provsql_arith_op``: PLUS / TIMES / MINUS / DIV / NEG / MAX / MIN / POW / LN / EXP / PERCENTILE) is stored in ``info1``. MAX / MIN are the order statistics behind ``greatest`` / ``least`` and the RV ``min`` / ``max`` aggregates; PERCENTILE is the ``percentile_cont`` order-statistic aggregate. * - ``gate_mixture`` - Probabilistic mixture of scalar random-variable roots gated by a Bernoulli weight. The wire vector is ``[p, x, y]`` for a Bernoulli mixture or ``[key, mul_1, …, mul_n]`` for a categorical block. * - ``gate_assumed`` - Single-child marker wrapping a per-row root computed under a provenance-class assumption; the assumption kind is a label in ``extra`` (``'boolean'`` from the safe-query rewriter, ``'absorptive'`` from cyclic-recursion truncation and the reachability route). Identity for compatible evaluators, fatal error for the rest; see :doc:`semiring-evaluation`. * - ``gate_annotation`` - Transparent single-child marker carrying an ``extra`` payload (the inversion-free certificate on a per-row root, or a per-input order key on an input). Unlike every other gate its UUID folds in ``extra`` (so two annotations over the same child with different ``extra`` are distinct gates); inert (identity) for every evaluator. See :ref:`inversion-free-path`. * - ``gate_conditioned`` - Conditioning marker with children ``[target, evidence]``: measure-only, ``probability_evaluate`` returns P(target ∧ evidence) / P(evidence) and the RV / ``agg_token`` evaluators the restricted distribution; terminal for the uuid carrier and refused by every general ``sr_*`` semiring (normalisation is not a semiring operation). * - ``gate_mobius`` - Signed Möbius combination: measure-only, one integer coefficient per child stored in ``extra`` (the ``gate_arith`` precedent); ``probability_evaluate`` returns Σᵢ coeffᵢ · P(childᵢ). The query's literal lineage is a designated transparent child (marked ``L:`` in ``extra``), so semiring evaluation, Shapley and named probability methods pass through to it. * - ``gate_case`` - ``N``-ary guarded selection over scalar (RV) children: wires ``[guard_1, value_1, …, guard_k, value_k, default]`` with first-match semantics (the value of the first guard event that holds, else the default). Backs a ``CASE`` over random variables (and ``abs`` / ``clamp`` / ReLU as sugar). Carries data only in its wires (the ``gate_conditioned`` precedent). RV/measure-carrier: real arms in the Monte-Carlo sampler, ``RangeCheck``, and the ``Expectation`` footprint, refused by every general ``sr_*`` semiring. * - ``gate_observe`` - Latent-variable observation (likelihood-weighting evidence): one wire → an observed bare ``gate_rv`` leaf, the observed datum in ``extra``. Contributes a continuous density factor (the leaf's pdf at the datum) instead of a Boolean truth value, composing into an evidence circuit by ``gate_times`` exactly like a conditioning event. Evaluated only by the importance-sampling weight walk (``Sampler::evalWeight``); refused by every Boolean / semiring evaluator (a density factor is not a semiring operation). See :doc:`continuous-distributions`. The random-variable gate types (``gate_rv``, ``gate_arith``, ``gate_mixture``, ``gate_case``), the marker gates (``gate_assumed``, ``gate_annotation``), the measure-only gates (``gate_conditioned``, ``gate_mobius``) and the evidence gate (``gate_observe``) are appended to the enum before ``gate_invalid``, with no renumbering of older values. See :doc:`continuous-distributions` for the full architecture of the continuous-distribution surface. ``gate_plus`` / ``gate_times`` gates may additionally carry a persisted d-DNNF certificate in ``info1`` (deterministic / decomposable by construction), stamped by the reachability and joint-width compilers and the certified HAVING enumerations, and consumed by the ``independent`` and ``interpret-as-dd`` evaluators (see :doc:`probability-evaluation`). Edges (wires) connect parent gates to their children, forming the provenance formula for each query result tuple.