feat: schedule due processing from next dueAt instead of polling

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

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]);
     }