[ColinLeeo]

Motivation

IterativeOptimizer logs every rule application at DEBUG level, but the before/after plan slots were filled with empty strings:

LOG.debug(DataNodeQueryMessages.RULE_S_BEFORE_S_AFTER_S, rule.getClass().getName(), "", "");

The message template is "Rule: {}\nBefore:\n{}\nAfter:\n{}", so enabling DEBUG for this logger produced a rule name followed by two blank sections — the log existed but carried no diagnostic value. This is a leftover from the initial table-model port; the placeholders were never filled in (verified via git log: they were already empty before the i18n conversion of this literal).

Changes

• IterativeOptimizer: render the node being rewritten and the transformed plan with the existing PlanGraphJsonPrinter, and pass them into the log.
• PlanGraphJsonPrinter: treat GroupReference as a leaf. Optimizer-internal nodes have GroupReference children, and GroupReference.getChildren() throws UnsupportedOperationException, which made both plan printers fail on such plans. This is a no-op for EXPLAIN, where group references never appear.
• Rule timing is now taken before logging, so enabling DEBUG no longer inflates the recorded rule execution time.

Rendering is best-effort and debug-gated: if rendering throws, the log falls back to the node's toString, so a debug log can never fail a query.

Example output

With DEBUG enabled for org.apache.iotdb.db.queryengine.plan.relational.planner.iterative.IterativeOptimizer:

Rule: ...rule.InlineProjections
Before:
{
  "name": "ProjectNode-8",
  "id": "8",
  "properties": {
    "OutputSymbols": ["device_id$gid", "count"],
    "Expressions": ["\"device_id$gid\"", "\"count\""]
  },
  "children": [{ "name": "GroupReference-19", "id": "19" }]
}
After:
{
  "name": "ProjectNode-8",
  ...
  "children": [{ "name": "GroupReference-20", "id": "20" }]
}

Test plan

• PlanGraphJsonPrinterTest — added testGroupReferenceIsRenderedAsLeaf, which renders a plan whose child is a GroupReference and asserts it is emitted as a leaf and that rendering does not throw.
• Ran PlanGraphJsonPrinterTest, PlanGraphPrinterTest and TableModelPlannerTest: 21 tests, 0 failures.
• End-to-end: built the distribution, enabled the DEBUG logger, ran a table-model query with a subquery; all 13 rule applications rendered real plans, with no fallback and no exception in the server log.

🤖 Generated with Claude Code