Polar tracing shows logs of how a query is evaluated.

Enabling Tracing

Debug mode is enabled by setting an environment variable: POLAR_LOG=1.

It will print out [debug] messages during query evaluation that show how the query is executed. Notable things include:

  • Queries and sub-query evaluations.

  • Showing values that are bound to variables for each expression.

  • Showing which rules a Polar predicate call will evaluate.

  • Showing values returned from calls into the application.


query> f(12);
[debug]   QUERY: f(12), BINDINGS: {}
[debug]     APPLICABLE_RULES: [
[debug]       f(x) if new (Foo{x: x}, _instance_2) and .(_instance_2, foo(), _value_1) and _value_1 = x;
[debug]       f(x) if x = 1;
[debug]       f(x) if x + 1 and _op_3 == 2;
[debug]     ]
[debug]     RULE:
[debug]     f(x) if
[debug]       new Foo(x: x).foo() = x
[debug]       QUERY: new (Foo{x: _x_10}, _instance_2_11) and .(_instance_2_11, foo(), _value_1_12) and _value_1_12 = _x_10, BINDINGS: {"_x_10": "12"}
[debug]         QUERY: new (Foo{x: _x_10}, _instance_2_11), BINDINGS: {"_x_10": "12"}
[debug]         QUERY: .(_instance_2_11, foo(), _value_1_12) and _value_1_12 = _x_10, BINDINGS: {"_instance_2_11": "Foo{x: 12}", "_x_10": "12"}
[debug]           QUERY: .(_instance_2_11, foo(), _value_1_12), BINDINGS: {"_instance_2_11": "Foo{x: 12}"}
[debug]             LOOKUP: Foo{x: 12}.foo()
[debug]             => 13
[debug]           QUERY: _value_1_12 = _x_10, BINDINGS: {"_x_10": "12", "_value_1_12": "13"}
[debug]             BACKTRACK
[debug]             LOOKUP: Foo{x: 12}.foo()
[debug]             => No more results.
[debug]             BACKTRACK
[debug]     RULE:
[debug]     f(x) if
[debug]       x = 1
[debug]       QUERY: _x_13 = 1, BINDINGS: {"_x_13": "12"}
[debug]         BACKTRACK
[debug]     RULE:
[debug]     f(x) if
[debug]       x + 1 == 2
[debug]       QUERY: _x_14 + 1 and _op_3_15 == 2, BINDINGS: {"_x_14": "12"}
[debug]         QUERY: _x_14 + 1, BINDINGS: {"_x_14": "12"}
[debug]           MATH: 12 + 1 = _op_3_15, BINDINGS: {}
[debug]         QUERY: _op_3_15 == 2, BINDINGS: {"_op_3_15": "13"}
[debug]           CMP: 13 == 2, BINDINGS: {}
[debug]           BACKTRACK
[debug]           HALT

Debug mode can be disabled by setting POLAR_LOG=0 or POLAR_LOG=off.

Set up a 1x1 with an Oso Engineer

Our team is happy to help you get started with Oso. If you'd like to learn more about using Oso in your app or have any questions about this guide, schedule a 1x1 with an Oso engineer.

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