feat: migrate Ordo schema with a dedicated Flyway history table

Stop rewriting spring.flyway.locations so host migrations stay independent and Boot 4 no longer needs starter-flyway for Ordo tables.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -1,6 +1,6 @@
 # Ordo
 
-轻量审批流程引擎。宿主通过 `OrdoEngine` 注册流程定义、发起实例、审批/驳回/转派/撤回/取消，并查询任务、实例与审计历史。引擎不绑定业务表单、用户体系或设计器 UI，当前也不自带 REST；业务数据放在 `ProcessContext` 里。
+轻量审批流程引擎。宿主通过 `OrdoEngine` 注册流程定义、发起实例、审批/驳回/转派/撤回/取消，并查询任务、实例与审计历史。引擎不绑定业务表单、用户体系或设计器 UI。可选 REST（`ordo.rest.enabled`）。业务数据放在 `ProcessContext` 里。
 
 要求 **Java 17+**。当前版本 `0.0.1-SNAPSHOT`。
 
@@ -14,7 +14,7 @@
 | `ordo-spring-boot-starter` | Spring Boot 自动装配（JDBC + Flyway） |
 | `ordo-example` | 内存引擎示例 |
 
-存储实现通过 dialect 层支持 **PostgreSQL** 与 **MySQL**（测试可用 H2 PostgreSQL 兼容模式）。Starter **不携带** JDBC 驱动，宿主自行加入 `postgresql`、`mysql-connector-j` 或 `h2`。Spring Boot 4 还需额外引入 `spring-boot-starter-flyway`，否则迁移不会跑。
+存储实现通过 dialect 层支持 **PostgreSQL** 与 **MySQL**（测试可用 H2 PostgreSQL 兼容模式）。Starter **不携带** JDBC 驱动，宿主自行加入 `postgresql`、`mysql-connector-j` 或 `h2`。表结构由 Ordo 自己的 Flyway 迁移（`ordo_schema_history`），与宿主 `spring.flyway` 无关。
 
 ## 能力
 
@@ -30,7 +30,7 @@
 - 审计时间线：`ProcessEvent` + `queryHistory`
 - 扩展点：`AssigneeResolver`、`RoutingCondition`、`ActionHandler`、`NamedCondition`、`NamedAction`、`OrdoEventListener`
 
-开发计划：可选 REST + 目录 SPI。设计器为独立产品（不进本仓库），待 REST 与目录之后。多租户 **暂不在计划中**。见 [docs/roadmap.md](docs/roadmap.md)。
+开发计划：独立设计器（不进本仓库）。多租户 **暂不在计划中**。见 [docs/roadmap.md](docs/roadmap.md)。
 
 详细用法（定义 JSON、扩展点、异常、查询、ACTION/审计语义）见 **[docs/usage.md](docs/usage.md)**。对外行为变更时同步更新该文档。
 
@@ -45,6 +45,12 @@
 ```
 
 ```java
+import com.jetlumen.ordo.api.OrdoEngine;
+import com.jetlumen.ordo.api.definition.ApprovalStep;
+import com.jetlumen.ordo.api.definition.ProcessDefinition;
+import com.jetlumen.ordo.api.runtime.ProcessContext;
+import com.jetlumen.ordo.core.InMemoryOrdoEngine;
+
 OrdoEngine ordo = new InMemoryOrdoEngine();
 ordo.publish(ProcessDefinition.linear("leave-request", "Leave request", List.of(
         ApprovalStep.single("manager", "Manager approval", "maria"),
@@ -83,8 +89,7 @@ ordo.approve(manager.id(), "maria", "ok");
 
 - `kind` 默认 `APPROVAL`；ACTION 用 `"action"` 作为 handler 查找键；`PARALLEL` 用 `branches`（结构化并行块，见 [docs/usage.md](docs/usage.md)）。
 - 带 `when` 的边先按 `priority` 匹配，都未命中再走无条件边；`to: null` 表示结束。
-- 代码侧可用 `ProcessDefinitionParser.fromJson(...)`。
-- `replace` 会整体替换同 id 定义；存在 `RUNNING` 实例时拒绝替换。
+- 代码侧可用 `ProcessDefinitionParser.fromJson(...)`（`com.jetlumen.ordo.api.definition`）。
 
 ## Spring Boot
 
@@ -96,7 +101,7 @@ ordo.approve(manager.id(), "maria", "ok");
 </dependency>
 ```
 
-需要 `DataSource`。存在 `DataSource` 且 `ordo.enabled` 不为 `false` 时装配 JDBC 引擎。
+需要 `DataSource`。存在 `DataSource` 且 `ordo.enabled` 不为 `false` 时装配 JDBC 引擎。REST 另需宿主的 Web starter，且 `ordo.rest.enabled=true`。
 
 ```yaml
 ordo:
@@ -105,6 +110,12 @@ ordo:
     dialect:     # 可选 postgresql / mysql；空则按 DataSource 探测
   definitions:
     location: classpath*:ordo/*.json   # 默认值；启动时 publish 加载
+  due:
+    poll-ms: 0   # >0 启用调度；值为最长空闲，按下次 dueAt 唤醒，满批续拉
+    batch-size: 100
+  rest:
+    enabled: false
+    base-path: /ordo
 ```
 
 宿主提供 Bean 即可覆盖默认值：
@@ -115,6 +126,7 @@ ordo:
 | `NamedCondition` / `NamedAction` | 可多个；无对应门面时按 key 分发 |
 | `RoutingCondition` | 无具名 condition 时始终匹配；有则未知 `ref` 为 false |
 | `ActionHandler` | 无具名 action 时空操作；有则未知 key 抛错 |
+| `OrdoCatalog` | REST 打开时从 Named* 投影；`assignees` 空 |
 | `OrdoEventListener` | 可注册多个，提交后按顺序调用 |
 
 ## 运行时约定

docs/ordo-rest.openapi.yaml

@@ -471,6 +471,7 @@ components:
               label:
                 type: string
     ProcessDefinitionDocument:
+      description: Closed document shape is docs/process-definition.schema.json. Graph rules are enforced by ProcessDefinitionParser.
       type: object
       required: [id, name, steps, transitions]
       properties:

docs/process-definition.schema.json

@@ -0,0 +1,297 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://jetlumen.com/ordo/schema/process-definition.json",
+  "title": "Ordo process definition document",
+  "$comment": "Document shape for ProcessDefinitionParser.fromJson. Graph connectivity, unique ids, PARALLEL membership, due.goto branch rules, and predicate depth/leaf limits are enforced only by the parser.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["id", "name", "steps", "transitions"],
+  "properties": {
+    "id": { "$ref": "#/$defs/nonEmptyString" },
+    "name": { "$ref": "#/$defs/nonEmptyString" },
+    "version": {
+      "type": "integer",
+      "minimum": 0,
+      "$comment": "Ignored by fromJson; written by toJson after publish."
+    },
+    "startStep": { "$ref": "#/$defs/nonEmptyString" },
+    "steps": {
+      "type": "array",
+      "minItems": 1,
+      "items": { "$ref": "#/$defs/topStep" }
+    },
+    "transitions": {
+      "type": "array",
+      "minItems": 1,
+      "items": { "$ref": "#/$defs/transition" }
+    }
+  },
+  "$defs": {
+    "nonEmptyString": {
+      "type": "string",
+      "pattern": ".*\\S.*"
+    },
+    "literal": {
+      "type": ["string", "number", "boolean"]
+    },
+    "topStep": {
+      "oneOf": [
+        { "$ref": "#/$defs/approvalStep" },
+        { "$ref": "#/$defs/actionStep" },
+        { "$ref": "#/$defs/parallelStep" }
+      ]
+    },
+    "leafStep": {
+      "oneOf": [
+        { "$ref": "#/$defs/approvalStep" },
+        { "$ref": "#/$defs/actionStep" }
+      ]
+    },
+    "approvalStep": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["id", "name", "candidates"],
+      "properties": {
+        "id": { "$ref": "#/$defs/nonEmptyString" },
+        "name": { "$ref": "#/$defs/nonEmptyString" },
+        "kind": { "const": "APPROVAL" },
+        "candidates": {
+          "type": "array",
+          "minItems": 1,
+          "uniqueItems": true,
+          "items": { "$ref": "#/$defs/nonEmptyString" }
+        },
+        "policy": { "type": "string", "enum": ["ANY", "ALL"] },
+        "due": { "$ref": "#/$defs/due" }
+      }
+    },
+    "actionStep": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["id", "name", "kind", "action"],
+      "properties": {
+        "id": { "$ref": "#/$defs/nonEmptyString" },
+        "name": { "$ref": "#/$defs/nonEmptyString" },
+        "kind": { "const": "ACTION" },
+        "action": { "$ref": "#/$defs/nonEmptyString" },
+        "policy": { "type": "string", "enum": ["ANY", "ALL"] }
+      }
+    },
+    "parallelStep": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["id", "name", "kind", "branches"],
+      "properties": {
+        "id": { "$ref": "#/$defs/nonEmptyString" },
+        "name": { "$ref": "#/$defs/nonEmptyString" },
+        "kind": { "const": "PARALLEL" },
+        "policy": { "type": "string", "enum": ["ANY", "ALL"] },
+        "branches": {
+          "type": "array",
+          "minItems": 2,
+          "items": { "$ref": "#/$defs/branch" }
+        }
+      }
+    },
+    "branch": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["id", "steps", "transitions"],
+      "properties": {
+        "id": { "$ref": "#/$defs/nonEmptyString" },
+        "steps": {
+          "type": "array",
+          "minItems": 1,
+          "items": { "$ref": "#/$defs/leafStep" }
+        },
+        "transitions": {
+          "type": "array",
+          "minItems": 1,
+          "items": { "$ref": "#/$defs/transition" }
+        }
+      }
+    },
+    "due": {
+      "oneOf": [
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["after", "then", "to"],
+          "properties": {
+            "after": { "$ref": "#/$defs/isoDuration" },
+            "then": { "const": "reassign" },
+            "to": { "$ref": "#/$defs/nonEmptyString" }
+          }
+        },
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["after", "then"],
+          "properties": {
+            "after": { "$ref": "#/$defs/isoDuration" },
+            "then": { "const": "notify" },
+            "action": { "$ref": "#/$defs/nonEmptyString" }
+          }
+        },
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "required": ["after", "then", "to"],
+          "properties": {
+            "after": { "$ref": "#/$defs/isoDuration" },
+            "then": { "const": "goto" },
+            "to": { "$ref": "#/$defs/nonEmptyString" }
+          }
+        }
+      ]
+    },
+    "isoDuration": {
+      "type": "string",
+      "minLength": 2,
+      "$comment": "java.time.Duration.parse; must be positive after parse."
+    },
+    "transition": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["from"],
+      "properties": {
+        "from": { "$ref": "#/$defs/nonEmptyString" },
+        "to": {
+          "type": ["string", "null"],
+          "minLength": 1
+        },
+        "when": { "$ref": "#/$defs/when" },
+        "priority": { "type": "integer" }
+      }
+    },
+    "when": {
+      "oneOf": [
+        { "$ref": "#/$defs/refWhen" },
+        { "$ref": "#/$defs/predicate" }
+      ]
+    },
+    "refWhen": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["ref"],
+      "properties": {
+        "ref": { "$ref": "#/$defs/nonEmptyString" },
+        "args": {
+          "type": "object",
+          "additionalProperties": true
+        }
+      }
+    },
+    "predicate": {
+      "oneOf": [
+        { "$ref": "#/$defs/compareEq" },
+        { "$ref": "#/$defs/compareNe" },
+        { "$ref": "#/$defs/compareGt" },
+        { "$ref": "#/$defs/compareGte" },
+        { "$ref": "#/$defs/compareLt" },
+        { "$ref": "#/$defs/compareLte" },
+        { "$ref": "#/$defs/inPredicate" },
+        { "$ref": "#/$defs/andPredicate" },
+        { "$ref": "#/$defs/orPredicate" },
+        { "$ref": "#/$defs/notPredicate" }
+      ]
+    },
+    "comparePair": {
+      "type": "array",
+      "minItems": 2,
+      "maxItems": 2,
+      "prefixItems": [
+        { "$ref": "#/$defs/nonEmptyString" },
+        { "$ref": "#/$defs/literal" }
+      ]
+    },
+    "compareEq": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["eq"],
+      "properties": { "eq": { "$ref": "#/$defs/comparePair" } }
+    },
+    "compareNe": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["ne"],
+      "properties": { "ne": { "$ref": "#/$defs/comparePair" } }
+    },
+    "compareGt": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["gt"],
+      "properties": { "gt": { "$ref": "#/$defs/comparePair" } }
+    },
+    "compareGte": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["gte"],
+      "properties": { "gte": { "$ref": "#/$defs/comparePair" } }
+    },
+    "compareLt": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["lt"],
+      "properties": { "lt": { "$ref": "#/$defs/comparePair" } }
+    },
+    "compareLte": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["lte"],
+      "properties": { "lte": { "$ref": "#/$defs/comparePair" } }
+    },
+    "inPredicate": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["in"],
+      "properties": {
+        "in": {
+          "type": "array",
+          "minItems": 2,
+          "maxItems": 2,
+          "prefixItems": [
+            { "$ref": "#/$defs/nonEmptyString" },
+            {
+              "type": "array",
+              "minItems": 1,
+              "items": { "$ref": "#/$defs/literal" }
+            }
+          ]
+        }
+      }
+    },
+    "andPredicate": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["and"],
+      "properties": {
+        "and": {
+          "type": "array",
+          "minItems": 1,
+          "items": { "$ref": "#/$defs/predicate" }
+        }
+      }
+    },
+    "orPredicate": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["or"],
+      "properties": {
+        "or": {
+          "type": "array",
+          "minItems": 1,
+          "items": { "$ref": "#/$defs/predicate" }
+        }
+      }
+    },
+    "notPredicate": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["not"],
+      "properties": {
+        "not": { "$ref": "#/$defs/predicate" }
+      }
+    }
+  }
+}

docs/roadmap.md

@@ -20,6 +20,7 @@
 - 管理员/系统取消 `cancel` / `CANCELLED`
 - 可选 REST（autoconfigure 条件装配）+ 目录 SPI `OrdoCatalog`
 - `NamedAction` / `NamedCondition` 注册与官方 key 分发；默认 Catalog 从具名 Bean 投影
+- API 分包：`api.definition` / `runtime` / `spi` / `util`
 
 ## 开发计划（确定要做）
 

docs/usage.md

@@ -22,7 +22,19 @@ Ordo 是嵌入宿主进程的审批引擎，入口是 `OrdoEngine`。
 | `ordo-spring-boot-starter` | Spring Boot 自动装配 |
 | `ordo-example` | `LeaveRequestExample` 内存演示 |
 
-Starter **不携带** JDBC 驱动。生产按库添加 `org.postgresql:postgresql` 或 `com.mysql:mysql-connector-j`。Spring Boot 4 还需 `spring-boot-starter-flyway`，否则 Flyway 迁移不会执行。
+Java 包（模块未变）：
+
+| 包 | 内容 |
+|---|---|
+| `com.jetlumen.ordo.api` | `OrdoEngine`、`TransactionExecutor` |
+| `com.jetlumen.ordo.api.definition` | 图：定义、步骤、边、`when`、PARALLEL |
+| `com.jetlumen.ordo.api.runtime` | 实例、任务、事件、ACTION 执行、token、`ProcessRuntime` |
+| `com.jetlumen.ordo.api.spi` | `ActionHandler`、`NamedAction`、`RoutingCondition`、`NamedCondition`、`AssigneeResolver`、`OrdoCatalog`、`OrdoEventListener` |
+| `com.jetlumen.ordo.api.util` | `Texts`、`Jsons` |
+| `com.jetlumen.ordo.api.exception` / `query` / `repository` | 异常、分页查询、存储端口 |
+| `com.jetlumen.ordo.core.spi` | `DispatchingActionHandler`、`DispatchingRoutingCondition`、`RegistryOrdoCatalog` |
+
+Starter **不携带** JDBC 驱动。生产按库添加 `org.postgresql:postgresql` 或 `com.mysql:mysql-connector-j`。Ordo 用独立 Flyway 建表，不依赖宿主 `spring.flyway`。
 
 先 `mvn install` 本仓库，宿主再依赖 `0.0.1-SNAPSHOT`。
 
@@ -60,10 +72,13 @@ ordo:
   enabled: true
   jdbc:
     dialect:     # 可选 postgresql / mysql；空则按 DataSource 探测
+    migrate: true
+    history-table: ordo_schema_history
   definitions:
     location: classpath*:ordo/*.json   # 启动时对每个 JSON 调用 publish
   due:
-    poll-ms: 0   # >0 时轮询 processDue；默认不调度
+    poll-ms: 0   # >0 启用调度；值为最长空闲，按下次 dueAt 唤醒，满批续拉
+    batch-size: 100
   rest:
     enabled: false
     base-path: /ordo
@@ -85,7 +100,7 @@ ordo:
 
 未提供 `NamedAction` 且未覆盖 `ActionHandler` 时，ACTION 步骤仍会推进流程，但 handler 什么都不做。不要同时提供门面 Bean 与对应 `Named*`（门面优先，具名 Bean 不参与运行时）。
 
-内存引擎把 `DispatchingRoutingCondition.of(...)` / `DispatchingActionHandler.of(...)` 传入 `InMemoryOrdoEngine` 即可。
+内存引擎把 `com.jetlumen.ordo.core.spi.DispatchingRoutingCondition.of(...)` / `DispatchingActionHandler.of(...)` 传入 `InMemoryOrdoEngine` 即可。
 
 ### 2.3 可选 REST
 
@@ -161,7 +176,7 @@ new ProcessDefinition("leave-request-routed", "Leave request",
 
 ### 3.2 JSON
 
-`ProcessDefinitionParser.fromJson(String|InputStream)` / `toJson(ProcessDefinition)`。Spring 默认扫 `classpath*:ordo/*.json`。`toJson` 写出 `version` 与 `startStep`（当前步骤列表首位）；`fromJson` 仍忽略 JSON 里的 `version`。
+`ProcessDefinitionParser.fromJson(String|InputStream)` / `toJson(ProcessDefinition)`。Spring 默认扫 `classpath*:ordo/*.json`。`toJson` 写出 `version` 与 `startStep`（当前步骤列表首位）；`fromJson` 仍忽略 JSON 里的 `version`。文档外形：[process-definition.schema.json](process-definition.schema.json)；图连通、PARALLEL 约束、谓词深度/叶子上限仍以解析器为准。
 
 ```json
 {
@@ -250,7 +265,8 @@ ordo.cancel(instance.id(), "admin", "政策变更");
 
 - `approve` / `reject` / `reassign`：`actor` 必须等于该任务当前 `assignee`，否则 `UnauthorizedTaskOperationException`。
 - `reassign`：仅 `PENDING` 任务；同一任务 id，办理人改为 `newAssignee`，不推进步骤。`newAssignee` 不可空白、不可等于当前 `assignee`，且同一步不能已有该人的 `PENDING` 任务，否则 `IllegalArgumentException`。不经过 `AssigneeResolver`。人工转派不改 `dueAt`。
-- `processDue(limit)`：认领 `dueAt <= now` 的 PENDING 任务（`limit > 0`），按步上 `due.then` 执行：`reassign` 换办理人（`to` 走 `AssigneeResolver`）、`notify` 可选 `ActionHandler`、`goto` 跳过当前步 PENDING 并进入 `to` 步骤（`to` 必须是步骤 id）。每种策略对一张任务最多成功一次（清空 `dueAt`）。引擎无后台线程；Spring 下 `ordo.due.poll-ms > 0` 才轮询。
+- `processDue(limit)`：认领 `dueAt <= now` 的 PENDING 任务（`limit > 0`），按步上 `due.then` 执行：`reassign` 换办理人（`to` 走 `AssigneeResolver`）、`notify` 可选 `ActionHandler`、`goto` 跳过当前步 PENDING 并进入 `to` 步骤（`to` 必须是步骤 id）。每种策略对一张任务最多成功一次（清空 `dueAt`）。引擎无后台线程；Spring 下 `ordo.due.poll-ms > 0` 才调度：按下次 `dueAt` 唤醒，满批续拉，`poll-ms` 为最长空闲。
+- `nextDueAt()`：PENDING 且仍有 `dueAt` 的最早到期时刻；没有则 empty。
 - 任务非 `PENDING`：`TaskAlreadyCompletedException`。
 - `withdraw`：仅 `initiator`，否则 `UnauthorizedInstanceOperationException`；实例非 `RUNNING`：`InstanceAlreadyCompletedException`。
 - `cancel`：`actor` 非空即可，**不校验**是否发起人；实例须为 `RUNNING`，否则 `InstanceAlreadyCompletedException`。谁能调用由宿主决定。
@@ -314,6 +330,10 @@ v1：至少 2 条分支；禁止套娃 PARALLEL；join 固定 ALL；任一分支
 **失败不回滚已提交的审批，不阻塞后续步骤，引擎不做重试。** 宿主用 `queryActionExecutions` 或 listener 自行补发。分发器遇到未知 `actionKey` 会抛 `IllegalArgumentException`，记为该次 ACTION `FAILED`。
 
 ```java
+import com.jetlumen.ordo.api.runtime.ProcessRuntime;
+import com.jetlumen.ordo.api.spi.NamedAction;
+import org.springframework.stereotype.Component;
+
 @Component
 public class LeaveApprovedMail implements NamedAction {
     @Override
@@ -376,6 +396,7 @@ ACTION 成功事件发生在提交之后，因此排在同轮事务内写入的
 | `approve` / `reject` | 办理当前 PENDING 任务 |
 | `reassign` | 当前办理人把 PENDING 任务转给他人 |
 | `processDue` | 认领并处理已到期 PENDING 任务 |
+| `nextDueAt` | 下一笔 PENDING 任务的 `dueAt` |
 | `withdraw` | 发起人撤回 |
 | `cancel` | 管理员/系统取消（引擎不鉴权角色） |
 | `find*` | 按 id / 待办索引读取 |
@@ -401,7 +422,7 @@ ACTION 成功事件发生在提交之后，因此排在同轮事务内写入的
 
 ## 12. 存储
 
-Flyway 脚本按方言分目录：`db/postgresql/migration`、`db/mysql/migration`。未设置 `spring.flyway.locations` 时，starter 按探测到的方言指向对应目录。已有 `flyway_schema_history` 的开发库按版本追加迁移（PARALLEL 为 `V3__parallel_blocks.sql`）。表包括流程头 `ordo_process`、按 `(id, version)` 存储的定义/步骤（含 `parent_step_id` / `branch_id`）/候选人/转移、实例（含 `definition_version`）、任务、并行令牌 `ordo_instance_token`、`ordo_process_event`、`ordo_action_execution`。
+Flyway 脚本按方言分目录：`db/postgresql/migration`、`db/mysql/migration`。Starter 在启动时用独立 Flyway 执行这些脚本，历史表默认 `ordo_schema_history`，不修改 `spring.flyway.locations`。若宿主也启用了 Spring Boot Flyway，Ordo 会在宿主 `flywayInitializer` 之后再 migrate，避免非空 schema 导致宿主失败。已有 `ordo_*` 表但尚无该历史表时，会 baseline 到当前脚本最高版本后再 migrate。`ordo.jdbc.migrate=false` 时不执行。表包括流程头 `ordo_process`、按 `(id, version)` 存储的定义/步骤（含 `parent_step_id` / `branch_id`）/候选人/转移、实例（含 `definition_version`）、任务、并行令牌 `ordo_instance_token`、`ordo_process_event`、`ordo_action_execution`。
 
 自定义方言：实现 `SqlDialect` 并用 `META-INF/services` 注册，或提供 `SqlDialect` Bean。新增列时每个已支持方言目录各加一条迁移。
 

ordo-api/src/main/java/com/jetlumen/ordo/api/OrdoEngine.java

@@ -11,6 +11,7 @@ import com.jetlumen.ordo.api.runtime.ProcessContext;
 import com.jetlumen.ordo.api.runtime.ProcessEvent;
 import com.jetlumen.ordo.api.runtime.ProcessInstance;
 
+import java.time.Instant;
 import java.util.List;
 import java.util.Optional;
 
@@ -40,6 +41,9 @@ public interface OrdoEngine {
     /** Claims and processes up to {@code limit} overdue pending tasks. {@code limit} must be positive. */
     int processDue(int limit);
 
+    /** Earliest {@code dueAt} among pending tasks, or empty if none are scheduled. */
+    Optional<Instant> nextDueAt();
+
     default ProcessInstance withdraw(String instanceId, String actor) {
         return withdraw(instanceId, actor, null);
     }

ordo-api/src/main/java/com/jetlumen/ordo/api/repository/ApprovalTaskRepository.java

@@ -43,6 +43,9 @@ public interface ApprovalTaskRepository {
 
     List<ApprovalTask> findDuePending(Instant now, int limit);
 
+    /** Earliest {@code dueAt} among pending tasks, or empty if none are scheduled. */
+    Optional<Instant> findNextDueAt();
+
     boolean claimIfDue(String taskId, String expectedAssignee, Instant now);
 
     /** Paginated, filterable query; results are ordered newest-first (created_at desc). */

ordo-core/src/main/java/com/jetlumen/ordo/core/DefaultOrdoEngine.java

@@ -345,6 +345,11 @@ public final class DefaultOrdoEngine implements OrdoEngine {
         return processed;
     }
 
+    @Override
+    public synchronized Optional<Instant> nextDueAt() {
+        return taskRepository.findNextDueAt();
+    }
+
     private boolean escalateDueTask(ApprovalTask overdue, Instant now, List<PendingAction> queued,
                                     List<ProcessEvent> events) {
         if (!taskRepository.claimIfDue(overdue.id(), overdue.assignee(), now)) {

ordo-core/src/main/java/com/jetlumen/ordo/core/InMemoryOrdoEngine.java

@@ -23,6 +23,7 @@ import com.jetlumen.ordo.core.repository.InMemoryProcessHistoryRepository;
 import com.jetlumen.ordo.core.repository.InMemoryProcessInstanceRepository;
 
 import java.time.Clock;
+import java.time.Instant;
 import java.util.List;
 import java.util.Optional;
 
@@ -181,4 +182,9 @@ public final class InMemoryOrdoEngine implements OrdoEngine {
     public int processDue(int limit) {
         return delegate.processDue(limit);
     }
+
+    @Override
+    public Optional<Instant> nextDueAt() {
+        return delegate.nextDueAt();
+    }
 }

ordo-core/src/main/java/com/jetlumen/ordo/core/repository/InMemoryApprovalTaskRepository.java

@@ -113,6 +113,15 @@ public final class InMemoryApprovalTaskRepository implements ApprovalTaskReposit
                 .toList();
     }
 
+    @Override
+    public synchronized Optional<Instant> findNextDueAt() {
+        return tasks.values().stream()
+                .filter(task -> task.status() == TaskStatus.PENDING)
+                .map(ApprovalTask::dueAt)
+                .filter(Objects::nonNull)
+                .min(Comparator.naturalOrder());
+    }
+
     @Override
     public synchronized boolean claimIfDue(String taskId, String expectedAssignee, Instant now) {
         ApprovalTask current = tasks.get(taskId);

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/OrdoDuePoller.java

@@ -5,24 +5,35 @@ import org.springframework.context.SmartLifecycle;
 
 import java.lang.System.Logger;
 import java.lang.System.Logger.Level;
+import java.time.Clock;
+import java.time.Instant;
 import java.util.Objects;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 
-/** Optional poller that calls {@link OrdoEngine#processDue(int)} when {@code ordo.due.poll-ms} is positive. */
+/** Optional scheduler that drains {@link OrdoEngine#processDue(int)} when {@code ordo.due.poll-ms} is positive. */
 public final class OrdoDuePoller implements SmartLifecycle {
     private static final Logger LOG = System.getLogger("ordo");
-    private static final int BATCH_SIZE = 100;
 
     private final OrdoEngine ordoEngine;
+    private final Clock clock;
     private final long pollMs;
+    private final int batchSize;
     private ScheduledExecutorService executor;
+    private ScheduledFuture<?> scheduled;
     private volatile boolean running;
+    private volatile boolean ticking;
 
-    public OrdoDuePoller(OrdoEngine ordoEngine, long pollMs) {
+    public OrdoDuePoller(OrdoEngine ordoEngine, Clock clock, long pollMs, int batchSize) {
         this.ordoEngine = Objects.requireNonNull(ordoEngine, "ordoEngine must not be null");
+        this.clock = Objects.requireNonNull(clock, "clock must not be null");
         this.pollMs = pollMs;
+        if (batchSize <= 0) {
+            throw new IllegalArgumentException("batch size must be positive");
+        }
+        this.batchSize = batchSize;
     }
 
     @Override
@@ -40,18 +51,51 @@ public final class OrdoDuePoller implements SmartLifecycle {
             thread.setDaemon(true);
             return thread;
         });
-        executor.scheduleWithFixedDelay(this::tick, pollMs, pollMs, TimeUnit.MILLISECONDS);
         running = true;
+        schedule(0);
+    }
+
+    void wake() {
+        if (!running || ticking) {
+            return;
+        }
+        schedule(0);
     }
 
     private void tick() {
+        ticking = true;
         try {
-            ordoEngine.processDue(BATCH_SIZE);
+            int processed;
+            do {
+                processed = ordoEngine.processDue(batchSize);
+            } while (processed == batchSize);
         } catch (RuntimeException e) {
             LOG.log(Level.WARNING, "processDue failed", e);
+        } finally {
+            if (running) {
+                schedule(nextDelayMs());
+            }
+            ticking = false;
         }
     }
 
+    private long nextDelayMs() {
+        Instant now = clock.instant();
+        return ordoEngine.nextDueAt()
+                .map(dueAt -> Math.min(Math.max(0L, dueAt.toEpochMilli() - now.toEpochMilli()), pollMs))
+                .orElse(pollMs);
+    }
+
+    private synchronized void schedule(long delayMs) {
+        if (!running || executor == null) {
+            return;
+        }
+        if (scheduled != null) {
+            scheduled.cancel(false);
+        }
+        scheduled = executor.schedule(this::tick, delayMs, TimeUnit.MILLISECONDS);
+    }
+
     @Override
     public void stop() {
         running = false;
@@ -59,6 +103,7 @@ public final class OrdoDuePoller implements SmartLifecycle {
             executor.shutdownNow();
             executor = null;
         }
+        scheduled = null;
     }
 
     @Override

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/OrdoDueWakeBridge.java

@@ -0,0 +1,25 @@
+package com.jetlumen.ordo.spring;
+
+import com.jetlumen.ordo.api.runtime.ProcessEvent;
+import com.jetlumen.ordo.api.runtime.ProcessEventType;
+import com.jetlumen.ordo.api.spi.OrdoEventListener;
+
+/** Forwards {@code TASK_CREATED} to {@link OrdoDuePoller} after the engine listener snapshot is taken. */
+public final class OrdoDueWakeBridge implements OrdoEventListener {
+    private volatile OrdoDuePoller poller;
+
+    public void attach(OrdoDuePoller poller) {
+        this.poller = poller;
+    }
+
+    @Override
+    public void onEvent(ProcessEvent event) {
+        if (event.type() != ProcessEventType.TASK_CREATED) {
+            return;
+        }
+        OrdoDuePoller current = poller;
+        if (current != null) {
+            current.wake();
+        }
+    }
+}

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/OrdoProperties.java

@@ -51,9 +51,12 @@ public class OrdoProperties {
     }
 
     public static class Due {
-        /** Poll interval in milliseconds. {@code 0} disables scheduling. */
+        /** Enables scheduling when positive; also the maximum idle sleep in milliseconds. */
         private long pollMs;
 
+        /** Tasks claimed per {@code processDue} call while draining. */
+        private int batchSize = 100;
+
         public long getPollMs() {
             return pollMs;
         }
@@ -61,12 +64,26 @@ public class OrdoProperties {
         public void setPollMs(long pollMs) {
             this.pollMs = pollMs;
         }
+
+        public int getBatchSize() {
+            return batchSize;
+        }
+
+        public void setBatchSize(int batchSize) {
+            this.batchSize = batchSize;
+        }
     }
 
     public static class Jdbc {
         /** Explicit dialect id ({@code postgresql}, {@code mysql}). Empty means detect from the DataSource. */
         private String dialect;
 
+        /** When true, Ordo runs its own Flyway against dialect locations. */
+        private boolean migrate = true;
+
+        /** Flyway history table used only by Ordo (not {@code flyway_schema_history}). */
+        private String historyTable = "ordo_schema_history";
+
         public String getDialect() {
             return dialect;
         }
@@ -74,6 +91,23 @@ public class OrdoProperties {
         public void setDialect(String dialect) {
             this.dialect = dialect;
         }
+
+        public boolean isMigrate() {
+            return migrate;
+        }
+
+        public void setMigrate(boolean migrate) {
+            this.migrate = migrate;
+        }
+
+        public String getHistoryTable() {
+            return historyTable;
+        }
+
+        public void setHistoryTable(String historyTable) {
+            this.historyTable = historyTable == null || historyTable.isBlank()
+                    ? "ordo_schema_history" : historyTable.trim();
+        }
     }
 
     public static class Rest {

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/jdbc/OrdoDatabaseInitializerDetector.java

@@ -0,0 +1,14 @@
+package com.jetlumen.ordo.spring.jdbc;
+
+import org.springframework.boot.sql.init.dependency.AbstractBeansOfTypeDatabaseInitializerDetector;
+
+import java.util.Set;
+
+/** Treats {@link OrdoSchemaMigrator} as database initialization for {@code @DependsOnDatabaseInitialization}. */
+public class OrdoDatabaseInitializerDetector extends AbstractBeansOfTypeDatabaseInitializerDetector {
+
+    @Override
+    protected Set<Class<?>> getDatabaseInitializerBeanTypes() {
+        return Set.of(OrdoSchemaMigrator.class);
+    }
+}

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/jdbc/OrdoFlywayAutoConfiguration.java

@@ -1,34 +1,22 @@
 package com.jetlumen.ordo.spring.jdbc;
 
 import com.jetlumen.ordo.spring.OrdoProperties;
-import com.jetlumen.ordo.storage.jdbc.dialect.SqlDialect;
-import com.jetlumen.ordo.storage.jdbc.dialect.SqlDialects;
 import org.flywaydb.core.Flyway;
-import org.flywaydb.core.api.configuration.FluentConfiguration;
-import org.springframework.beans.factory.FactoryBean;
+import org.springframework.beans.factory.BeanFactory;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
-import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
-import org.springframework.core.env.Environment;
 
 import javax.sql.DataSource;
-import java.lang.reflect.Proxy;
 
 /**
- * Points Flyway at the dialect migration directory before Flyway runs.
- * Host {@code spring.flyway.locations} is left unchanged when set.
- *
- * <p>Does not inject {@link DataSource} or {@link SqlDialect} at bean-creation time
- * (that would cycle with DataSource → Flyway → customizer). Dialect is resolved inside
- * {@code customize} from the FluentConfiguration DataSource / {@code ordo.jdbc.dialect}.
- *
- * <p>FlywayConfigurationCustomizer moved between Boot 3 and Boot 4; a reflective
- * {@link FactoryBean} supplies a proxy for whichever type is on the classpath.
+ * Migrates Ordo tables with a dedicated Flyway history table, independent of
+ * {@code spring.flyway}. Runs after the host {@code flywayInitializer} when present so a
+ * non-empty schema does not break host migrate.
  */
 @AutoConfiguration
 @ConditionalOnProperty(prefix = "ordo", name = "enabled", havingValue = "true", matchIfMissing = true)
@@ -36,89 +24,19 @@ import java.lang.reflect.Proxy;
 @ConditionalOnBean(DataSource.class)
 @AutoConfigureAfter(name = {
         "org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration",
-        "org.springframework.boot.jdbc.autoconfigure.DataSourceAutoConfiguration"
-})
-@AutoConfigureBefore(name = {
+        "org.springframework.boot.jdbc.autoconfigure.DataSourceAutoConfiguration",
         "org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration",
         "org.springframework.boot.flyway.autoconfigure.FlywayAutoConfiguration"
 })
 @EnableConfigurationProperties(OrdoProperties.class)
 public class OrdoFlywayAutoConfiguration {
 
-    private static final String[] FLYWAY_CUSTOMIZER_TYPES = {
-            "org.springframework.boot.flyway.autoconfigure.FlywayConfigurationCustomizer",
-            "org.springframework.boot.autoconfigure.flyway.FlywayConfigurationCustomizer"
-    };
-
     @Bean
-    @ConditionalOnClass(name = "org.flywaydb.core.api.configuration.FluentConfiguration")
-    public FactoryBean<Object> ordoFlywayConfigurationCustomizer(
-            OrdoProperties ordoProperties, Environment environment) {
-        Class<?> customizerType = resolveFlywayCustomizerType();
-        if (customizerType == null) {
-            return null;
-        }
-        return new FlywayLocationsCustomizerFactoryBean(customizerType, ordoProperties, environment);
-    }
-
-    static Class<?> resolveFlywayCustomizerType() {
-        ClassLoader classLoader = OrdoFlywayAutoConfiguration.class.getClassLoader();
-        for (String name : FLYWAY_CUSTOMIZER_TYPES) {
-            try {
-                return Class.forName(name, false, classLoader);
-            } catch (ClassNotFoundException ignored) {
-                // Boot 3 vs Boot 4
-            }
-        }
-        return null;
-    }
-
-    private static final class FlywayLocationsCustomizerFactoryBean implements FactoryBean<Object> {
-        private final Class<?> customizerType;
-        private final OrdoProperties ordoProperties;
-        private final Environment environment;
-
-        private FlywayLocationsCustomizerFactoryBean(Class<?> customizerType, OrdoProperties ordoProperties,
-                                                     Environment environment) {
-            this.customizerType = customizerType;
-            this.ordoProperties = ordoProperties;
-            this.environment = environment;
-        }
-
-        @Override
-        public Object getObject() {
-            return Proxy.newProxyInstance(customizerType.getClassLoader(), new Class<?>[] {customizerType},
-                    (proxy, method, args) -> {
-                        String name = method.getName();
-                        if ("customize".equals(name) && args != null && args.length == 1) {
-                            applyLocations((FluentConfiguration) args[0]);
-                            return null;
-                        }
-                        if ("equals".equals(name)) {
-                            return proxy == args[0];
-                        }
-                        if ("hashCode".equals(name)) {
-                            return System.identityHashCode(proxy);
-                        }
-                        if ("toString".equals(name)) {
-                            return "OrdoFlywayLocationsCustomizer";
-                        }
-                        throw new UnsupportedOperationException(method.toString());
-                    });
-        }
-
-        private void applyLocations(FluentConfiguration configuration) {
-            if (environment.containsProperty("spring.flyway.locations")) {
-                return;
-            }
-            SqlDialect dialect = SqlDialects.resolve(configuration.getDataSource(),
-                    ordoProperties.getJdbc().getDialect());
-            configuration.locations(dialect.flywayLocations());
-        }
-
-        @Override
-        public Class<?> getObjectType() {
-            return customizerType;
+    public OrdoSchemaMigrator ordoSchemaMigrator(DataSource dataSource, OrdoProperties ordoProperties,
+                                                 BeanFactory beanFactory) {
+        if (beanFactory.containsBean("flywayInitializer")) {
+            beanFactory.getBean("flywayInitializer");
         }
+        return new OrdoSchemaMigrator(dataSource, ordoProperties);
     }
 }

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/jdbc/OrdoJdbcAutoConfiguration.java

@@ -19,6 +19,7 @@ import com.jetlumen.ordo.core.spi.DispatchingActionHandler;
 import com.jetlumen.ordo.core.spi.DispatchingRoutingCondition;
 import com.jetlumen.ordo.spring.OrdoDefinitionLoader;
 import com.jetlumen.ordo.spring.OrdoDuePoller;
+import com.jetlumen.ordo.spring.OrdoDueWakeBridge;
 import com.jetlumen.ordo.spring.OrdoProperties;
 import com.jetlumen.ordo.storage.jdbc.JdbcActionExecutionRepository;
 import com.jetlumen.ordo.storage.jdbc.JdbcApprovalTaskRepository;
@@ -152,6 +153,12 @@ public class OrdoJdbcAutoConfiguration {
         return new JdbcInstanceTokenRepository(connectionProvider, ordoSqlDialect);
     }
 
+    @Bean
+    @ConditionalOnMissingBean
+    public OrdoDueWakeBridge ordoDueWakeBridge() {
+        return new OrdoDueWakeBridge();
+    }
+
     @Bean
     @ConditionalOnMissingBean
     public OrdoEngine ordoEngine(Clock ordoClock,
@@ -181,7 +188,11 @@ public class OrdoJdbcAutoConfiguration {
 
     @Bean
     @ConditionalOnMissingBean
-    public OrdoDuePoller ordoDuePoller(OrdoEngine ordoEngine, OrdoProperties ordoProperties) {
-        return new OrdoDuePoller(ordoEngine, ordoProperties.getDue().getPollMs());
+    public OrdoDuePoller ordoDuePoller(OrdoEngine ordoEngine, Clock ordoClock, OrdoProperties ordoProperties,
+                                      OrdoDueWakeBridge ordoDueWakeBridge) {
+        OrdoDuePoller poller = new OrdoDuePoller(ordoEngine, ordoClock, ordoProperties.getDue().getPollMs(),
+                ordoProperties.getDue().getBatchSize());
+        ordoDueWakeBridge.attach(poller);
+        return poller;
     }
 }

ordo-spring-boot-autoconfigure/src/main/java/com/jetlumen/ordo/spring/jdbc/OrdoSchemaMigrator.java

@@ -0,0 +1,86 @@
+package com.jetlumen.ordo.spring.jdbc;
+
+import com.jetlumen.ordo.spring.OrdoProperties;
+import com.jetlumen.ordo.storage.jdbc.dialect.SqlDialects;
+import org.flywaydb.core.Flyway;
+import org.flywaydb.core.api.MigrationInfo;
+import org.flywaydb.core.api.MigrationVersion;
+import org.flywaydb.core.api.configuration.FluentConfiguration;
+
+import javax.sql.DataSource;
+import java.sql.Connection;
+import java.sql.DatabaseMetaData;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.Locale;
+
+/**
+ * Runs Ordo Flyway scripts independently of the host {@code spring.flyway} instance.
+ * Presence of this bean marks Ordo schema initialization for
+ * {@code @DependsOnDatabaseInitialization}.
+ */
+public final class OrdoSchemaMigrator {
+
+    private static final String PROCESS_TABLE = "ordo_process";
+
+    public OrdoSchemaMigrator(DataSource dataSource, OrdoProperties properties) {
+        OrdoProperties.Jdbc jdbc = properties.getJdbc();
+        if (!jdbc.isMigrate()) {
+            return;
+        }
+        String[] locations = SqlDialects.resolve(dataSource, jdbc.getDialect()).flywayLocations();
+        String historyTable = jdbc.getHistoryTable();
+        FluentConfiguration configuration = new FluentConfiguration(OrdoSchemaMigrator.class.getClassLoader())
+                .dataSource(dataSource)
+                .locations(locations)
+                .table(historyTable);
+        applyBaselineIfNeeded(configuration, dataSource, historyTable);
+        configuration.load().migrate();
+    }
+
+    private static void applyBaselineIfNeeded(FluentConfiguration configuration, DataSource dataSource,
+                                              String historyTable) {
+        try (Connection connection = dataSource.getConnection()) {
+            DatabaseMetaData metaData = connection.getMetaData();
+            if (tableExists(metaData, connection, historyTable)) {
+                return;
+            }
+            // Host tables / flyway_schema_history make the schema non-empty; Flyway then requires
+            // baseline before migrate. Existing Ordo tables baseline to latest (skip scripts);
+            // otherwise baseline at 0 so V1+ still run.
+            if (tableExists(metaData, connection, PROCESS_TABLE)) {
+                MigrationVersion latest = latestVersion(configuration.load());
+                configuration.baselineOnMigrate(true).baselineVersion(latest);
+            } else {
+                configuration.baselineOnMigrate(true).baselineVersion(MigrationVersion.fromVersion("0"));
+            }
+        } catch (SQLException e) {
+            throw new IllegalStateException("failed to inspect schema before Ordo Flyway migrate", e);
+        }
+    }
+
+    private static boolean tableExists(DatabaseMetaData metaData, Connection connection, String table)
+            throws SQLException {
+        String catalog = connection.getCatalog();
+        String schema = connection.getSchema();
+        String[] names = {table, table.toLowerCase(Locale.ROOT), table.toUpperCase(Locale.ROOT)};
+        for (String name : names) {
+            try (ResultSet tables = metaData.getTables(catalog, schema, name, new String[] {"TABLE"})) {
+                if (tables.next()) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    private static MigrationVersion latestVersion(Flyway flyway) {
+        MigrationVersion latest = MigrationVersion.fromVersion("0");
+        for (MigrationInfo info : flyway.info().all()) {
+            if (info.getVersion() != null && info.getVersion().compareTo(latest) > 0) {
+                latest = info.getVersion();
+            }
+        }
+        return latest;
+    }
+}

ordo-spring-boot-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.sql.init.dependency.DatabaseInitializerDetector.imports

@@ -0,0 +1 @@
+com.jetlumen.ordo.spring.jdbc.OrdoDatabaseInitializerDetector

ordo-spring-boot-autoconfigure/src/test/java/com/jetlumen/ordo/spring/jdbc/OrdoJdbcAutoConfigurationTest.java

@@ -73,7 +73,7 @@ class OrdoJdbcAutoConfigurationTest {
 
     @Test
     void honoursExplicitMysqlDialect() {
-        withDataSourceRunner.withPropertyValues("ordo.jdbc.dialect=mysql", "spring.flyway.enabled=false")
+        withDataSourceRunner.withPropertyValues("ordo.jdbc.dialect=mysql", "ordo.jdbc.migrate=false")
                 .run(context -> assertThat(context.getBean(SqlDialect.class).id()).isEqualTo("mysql"));
     }
 

ordo-storage-jdbc/src/main/java/com/jetlumen/ordo/storage/jdbc/JdbcApprovalTaskRepository.java

@@ -11,6 +11,7 @@ import com.jetlumen.ordo.storage.jdbc.dialect.SqlDialects;
 import com.jetlumen.ordo.storage.jdbc.mapper.ApprovalTaskMapper;
 
 import java.sql.Connection;
+import java.sql.DatabaseMetaData;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
@@ -18,6 +19,7 @@ import java.sql.Timestamp;
 import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 
@@ -52,6 +54,8 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
     private static final String SELECT_DUE_PENDING_BASE =
             "SELECT " + TASK_COLUMNS + " FROM ordo_approval_task WHERE status = 'PENDING' AND due_at IS NOT NULL"
                     + " AND due_at <= ? ORDER BY due_at, id";
+    private static final String SELECT_NEXT_DUE_AT =
+            "SELECT MIN(due_at) FROM ordo_approval_task WHERE status = 'PENDING' AND due_at IS NOT NULL";
     private static final String TASK_COLUMNS_QUALIFIED =
             "t.id, t.instance_id, t.step_id, t.task_name, t.assignee, t.status, t.created_at, t.completed_at,"
                     + " t.action_actor, t.action_comment, t.action_at, t.due_at";
@@ -67,7 +71,7 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
     public JdbcApprovalTaskRepository(JdbcConnectionProvider connectionProvider, SqlDialect dialect) {
         this.connectionProvider = Objects.requireNonNull(connectionProvider, "connectionProvider must not be null");
         this.dialect = Objects.requireNonNull(dialect, "dialect must not be null");
-        this.selectDuePending = dialect.limit(SELECT_DUE_PENDING_BASE, false);
+        this.selectDuePending = duePendingSql(this.connectionProvider, this.dialect);
     }
 
     @Override
@@ -180,6 +184,23 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
         }
     }
 
+    @Override
+    public Optional<Instant> findNextDueAt() {
+        Connection connection = connectionProvider.getConnection();
+        try (PreparedStatement select = connection.prepareStatement(SELECT_NEXT_DUE_AT);
+             ResultSet resultSet = select.executeQuery()) {
+            if (!resultSet.next()) {
+                return Optional.empty();
+            }
+            Timestamp timestamp = resultSet.getTimestamp(1);
+            return timestamp == null ? Optional.empty() : Optional.of(timestamp.toInstant());
+        } catch (SQLException e) {
+            throw new JdbcStorageException("failed to query next due at", e);
+        } finally {
+            connectionProvider.close(connection);
+        }
+    }
+
     @Override
     public boolean claimIfDue(String taskId, String expectedAssignee, Instant now) {
         Objects.requireNonNull(taskId, "taskId must not be null");
@@ -275,6 +296,24 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
         }
     }
 
+    private static String duePendingSql(JdbcConnectionProvider connectionProvider, SqlDialect dialect) {
+        String limited = dialect.limit(SELECT_DUE_PENDING_BASE, false);
+        return supportsSkipLocked(connectionProvider) ? dialect.forUpdateSkipLocked(limited) : limited;
+    }
+
+    private static boolean supportsSkipLocked(JdbcConnectionProvider connectionProvider) {
+        Connection connection = connectionProvider.getConnection();
+        try {
+            DatabaseMetaData metaData = connection.getMetaData();
+            String product = metaData.getDatabaseProductName();
+            return product != null && !product.toLowerCase(Locale.ROOT).contains("h2");
+        } catch (SQLException e) {
+            return false;
+        } finally {
+            connectionProvider.close(connection);
+        }
+    }
+
     private List<ApprovalTask> findAll(String sql, String parameter) {
         Connection connection = connectionProvider.getConnection();
         try (PreparedStatement select = connection.prepareStatement(sql)) {

ordo-storage-jdbc/src/main/java/com/jetlumen/ordo/storage/jdbc/dialect/LimitOffsetSqlDialect.java

@@ -16,4 +16,9 @@ abstract class LimitOffsetSqlDialect implements SqlDialect {
     public final String forUpdate(String sql) {
         return sql + " FOR UPDATE";
     }
+
+    @Override
+    public final String forUpdateSkipLocked(String sql) {
+        return sql + " FOR UPDATE SKIP LOCKED";
+    }
 }

ordo-storage-jdbc/src/main/java/com/jetlumen/ordo/storage/jdbc/dialect/SqlDialect.java

@@ -25,5 +25,8 @@ public interface SqlDialect {
 
     String forUpdate(String sql);
 
+    /** Appends {@code FOR UPDATE SKIP LOCKED}. */
+    String forUpdateSkipLocked(String sql);
+
     String[] flywayLocations();
 }

ordo-storage-jdbc/src/test/java/com/jetlumen/ordo/storage/jdbc/dialect/SqlDialectsTest.java

@@ -54,6 +54,7 @@ class SqlDialectsTest {
         assertEquals("SELECT 1 LIMIT ? OFFSET ?", dialect.limit("SELECT 1"));
         assertEquals("SELECT 1 LIMIT ?", dialect.limit("SELECT 1", false));
         assertEquals("SELECT 1 FOR UPDATE", dialect.forUpdate("SELECT 1"));
+        assertEquals("SELECT 1 FOR UPDATE SKIP LOCKED", dialect.forUpdateSkipLocked("SELECT 1"));
         assertEquals("classpath:db/postgresql/migration", dialect.flywayLocations()[0]);
     }