feat: v0.2.4 异步Compaction + 槽位压缩 + EXPLAIN + 慢查询日志

src/query/executor.ts

@@ -26,6 +26,7 @@ export class QueryExecutor {
   async execute(stmt: Statement): Promise<unknown> {
     switch (stmt.type) {
       case 'SELECT': return this.executeSelect(stmt);
+      case 'EXPLAIN': return this.executeExplain(stmt as any);
       case 'INSERT': return this.executeInsert(stmt);
       case 'UPDATE': return this.executeUpdate(stmt);
       case 'DELETE': return this.executeDelete(stmt);
@@ -35,6 +36,31 @@ export class QueryExecutor {
     }
   }
 
+  /** EXPLAIN: 输出查询计划 */
+  private async executeExplain(stmt: { query: Statement }): Promise<Record<string, unknown>> {
+    const plan = compileStatement(stmt.query.type === 'SELECT' ? stmt.query : stmt.query as any);
+    const startTime = Date.now();
+    let result: unknown = null;
+    try {
+      result = await this.execute(stmt.query);
+    } catch { /* explain 即使执行失败也返回计划 */ }
+    const elapsed = Date.now() - startTime;
+    const rows = Array.isArray(result) ? result.length : 0;
+
+    return {
+      type: stmt.query.type,
+      table: plan.table,
+      columns: plan.columns,
+      where: plan.where || {},
+      orderBy: plan.orderBy || [],
+      limit: plan.limit,
+      offset: plan.offset,
+      usingIndex: plan.table ? 'auto' : 'none',
+      estimatedRows: rows,
+      actualTimeMs: elapsed,
+    };
+  }
+
   // ===================================================================
   //  SELECT
   // ===================================================================