tree_decomposition_dot.cpp

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/**
 * @file tree_decomposition_dot.cpp
 * @brief SQL function @c provsql.tree_decomposition_dot() – return a
 *        GraphViz DOT visualisation of the tree decomposition of the
 *        provenance circuit's primal graph.
 *
 * The same min-fill decomposition that backs
 * @c probability_evaluate(..., 'tree-decomposition') is exposed here as
 * a DOT digraph, with the computed treewidth attached as a
 * @c "// treewidth=..." comment on the first line.
 */
extern "C" {
#include "postgres.h"
#include "fmgr.h"
#if PG_VERSION_NUM >= 160000
#include "varatt.h"
#endif
#include "catalog/pg_type.h"
#include "utils/uuid.h"
#include "provsql_shmem.h"
#include "provsql_utils.h"
 
PG_FUNCTION_INFO_V1(tree_decomposition_dot);
}
 
#include "c_cpp_compatibility.h"
#include "BooleanCircuit.h"
#include "CircuitFromMMap.h"
#include "TreeDecomposition.h"
#include "provsql_utils_cpp.h"
 
#include <string>
 
using namespace std;
 
/**
 * @brief PostgreSQL-callable entry point.
 *
 * Arguments: @c token (uuid).
 * Returns: DOT text whose first line is @c "// treewidth=<n>".
 */
Datum tree_decomposition_dot(PG_FUNCTION_ARGS)
{
  try {
    if(PG_ARGISNULL(0))
      PG_RETURN_NULL();
    pg_uuid_t *token = DatumGetUUIDP(PG_GETARG_DATUM(0));
 
    gate_t root;
    BooleanCircuit c = getBooleanCircuit(*token, root);
    c.rewriteMultivaluedGates();
 
    try {
      TreeDecomposition td(c);
      // Two preamble lines before the digraph body:
      //
      //   // treewidth=<n>
      //   // inputs: <idx>=<uuid> <idx>=<uuid> ...
      //
      // The second line maps BooleanCircuit gate indices (the same
      // indices that appear inside each bag's `{...}` label) back to
      // the original provenance UUID, when the gate is a tracked input
      // leaf.  Bag indices not present in the map are post-Tseytin
      // auxiliary gates with no source row.  The Studio reads this map
      // to enrich the bag inspector: input variables get a clickable
      // chip pointing at /api/leaf/<uuid>, auxiliaries stay opaque.
      string inputs_line = "// inputs:";
      for (gate_t in : c.getInputs()) {
        const string &uuid = c.getUUID(in);
        if (uuid.empty()) continue;
        inputs_line += " " + to_string(in) + "=" + uuid;
      }
      inputs_line += "\n";
 
      string dot = "// treewidth=" + to_string(td.getTreewidth()) + "\n"
                   + inputs_line
                   + td.toDot();
      text *result = (text *) palloc(VARHDRSZ + dot.size());
      SET_VARSIZE(result, VARHDRSZ + dot.size());
      memcpy((void *) VARDATA(result), dot.c_str(), dot.size());
      PG_RETURN_TEXT_P(result);
    } catch(TreeDecompositionException &) {
      provsql_error(
        "circuit treewidth exceeds the supported limit (MAX_TREEWIDTH)");
    }
  } catch(const std::exception &e) {
    provsql_error("%s", e.what());
  } catch(...) {
    provsql_error("Unknown exception");
  }
  PG_RETURN_NULL();
}