很迷惑为什么PostgreSQL这样优秀的一个项目总是不被接受，网上搜出的和MySQL的对比都在说PostgreSQL比MySQL慢得多，而证据都是三四年前的某个测试数据。昨晚找到了一个09年6月的帖子，测试方式还算比较严谨，数据在上面的链接里可以看到，作者得出了以下结论：

• MySQL 5.0.51a-24+lenny1 – Debian stable version is the worst performer (also the MySQL version is a little bit old).
• MySQL 5.1.30/InnoDB 1.0.3 with Google SMP patch – Compiled by SUN and InnoDB compiled by ORACLE outperform PostgreSQL in some cases.
• PostgreSQL 8.3.7-0lenny1 – Debian Stable version – It’s a top performer from the Debian standard distro and is out performed only by the latest InnoDB 1.0.3.
• Differences between PostgreSQL and MySQL 5.1.30/InnoDB 1.0.3 are very small
• PostgreSQL is outperforming any MySQL version on Creating, Loading, Created Indexes operations (this can be very usefull on a DB recovery).
• I don’t know why PostgreSQL is performing bad on bulk_delete() bulk_modify() querys … is possible to have a glitch in my configurations?

除了一个批量删除和批量修改的操作PostgreSQL慢的有点离谱（和MySQL相差6000多倍），应该能算是个Bug了，其他的性能大多还是比MySQL要好的。当然这里都是和InnoDB比较的，若是和MyISAM相比的话，慢点儿也是正常，因为MyISAM的功能太少，少了很多必要的操作和约束，对于任何一个业务系统，没有事务支持都是肯定不行的，不过这在MySQL的主要应用领域——网站上并不是个大问题。

数据库只有三个字段：

id     varchar(36)   Workflow Guid
state   blob              Workflow State Serialized
status    tinyint       Workflow  Status

代码如下：

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Workflow.ComponentModel;
using System.Workflow.Runtime;
using System.Workflow.Runtime.Hosting;
using Microsoft.Practices.EnterpriseLibrary.Data;

namespace Ganji.OA.Workflow
{
    public class MysqlWorkflowPersistenceService : WorkflowPersistenceService
    {
        public MysqlWorkflowPersistenceService()
            : base()
        {}

        public List GetAllWorkflows()
        {
            List result = new List();
            Database db = DatabaseFactory.CreateDatabase("OAData");
            DbCommand command = db.GetSqlStringCommand("SELECT id FROM workflow_state");
            DbDataReader reader = command.ExecuteReader();
            while (reader.Read())
            {
                result.Add(new Guid((string)reader["id"]));
            }
            reader.Close();
            return result;
        }

        protected override Activity LoadCompletedContextActivity(Guid scopeId, Activity outerActivity)
        {
            Guid instanceId = WorkflowEnvironment.WorkflowInstanceId;
            Activity activity = Deserialize(instanceId, scopeId, outerActivity);
            return activity;
        }

        protected override Activity LoadWorkflowInstanceState(Guid instanceId)
        {
            Activity activity = Deserialize(instanceId, Guid.Empty, null);
            return activity;
        }

        protected override void SaveCompletedContextActivity(Activity activity)
        {
            Guid instanceId = WorkflowEnvironment.WorkflowInstanceId;
            Guid contextId = (Guid)activity.GetValue(Activity.ActivityContextGuidProperty);
            Serialize(instanceId, contextId, activity);
        }

        protected override void SaveWorkflowInstanceState(Activity rootActivity, bool unlock)
        {
            WorkflowStatus status = GetWorkflowStatus(rootActivity);
            Guid instanceId = WorkflowEnvironment.WorkflowInstanceId;

            if (status == WorkflowStatus.Terminated || status == WorkflowStatus.Completed)
            {
                DeleteWorkflow(instanceId);
            }
            else
            {
                Serialize(instanceId, Guid.Empty, rootActivity);
            }
        }

        protected override bool UnloadOnIdle(Activity activity)
        {
            return true;
        }

        protected override void UnlockWorkflowInstanceState(Activity rootActivity)
        {
        }

        private void Serialize(Guid instanceId, Guid contextId, Activity activity)
        {
            byte[] state = WorkflowPersistenceService.GetDefaultSerializedForm(activity);
            Database db = DatabaseFactory.CreateDatabase("OAData");
            String sql_del = "DELETE FROM workflow_state WHERE id=@id";
            DbCommand command_del = db.GetSqlStringCommand(sql_del);
            db.AddInParameter(command_del, "@id", DbType.String, instanceId.ToString());

            String sql = "INSERT INTO workflow_state (`id`, `state`, `status`) VALUES (@id, @state, @status)";
            DbCommand command = db.GetSqlStringCommand(sql);
            db.AddInParameter(command, "@id", DbType.String, instanceId.ToString());
            db.AddInParameter(command, "@state", DbType.Binary, state);
            db.AddInParameter(command, "@status", DbType.Byte, 0);

            using (DbConnection conn = db.CreateConnection())
            {
                conn.Open();
                db.ExecuteNonQuery(command_del);
                db.ExecuteNonQuery(command);
                conn.Close();
            }
        }

        private Activity Deserialize(Guid instanceId, Guid contextId, Activity outerActivity)
        {
            Database db = DatabaseFactory.CreateDatabase("OAData");
            string sql = "SELECT * FROM workflow_state WHERE id='" + instanceId.ToString() + "'";
            Activity activity = null;
            using (DbDataReader reader = db.ExecuteReader(CommandType.Text, sql) as DbDataReader)
            {
                if (reader.HasRows)
                {
                    reader.Read();
                    byte[] state = (byte[])reader["state"];
                    reader.Close();
                    activity = WorkflowPersistenceService.RestoreFromDefaultSerializedForm(state, outerActivity);
                }
            }
            return activity;
        }

        private void DeleteWorkflow(Guid instanceId)
        {
            Database db = DatabaseFactory.CreateDatabase("OAData");
            string sql = "DELETE FROM workflow_state WHERE id=@id";
            DbCommand command = db.GetSqlStringCommand(sql);
            db.AddInParameter(command, "@id", DbType.String, instanceId.ToString());
            using (DbConnection conn = db.CreateConnection())
            {
                conn.Open();
                command.ExecuteNonQuery();
                conn.Close();
            }
        }
    }
}

重要更正: 在Pro WF书里说保存和恢复Activity的状态是用的Activity对象的Save和Load方法，这样保存的对象信息有六十多KB，还只是对于一个只有5个状态的小工作流，这个尺寸放在MySQL的blob里都放不下，造成了运行时一开始可以正常的存入工作流状态，但状态变更后，工作流序列化后的对象增大，保存进数据库的时候被截断了，造成了下次从数据库取得状态时报一个“在分析完成之前就遇到流结尾。”的错误，浪费了近一天的时间去解决这个问题。最终在MSDN的一篇文章的一小段例子里，看到它恢复Activity状态用的是WorkflowPersistenceService对象的这个方法

protected static Activity RestoreFromDefaultSerializedForm(
	byte[] activityBytes,
	Activity outerActivity
)

相应的保存Activity状态的方法是：
protected static byte[] GetDefaultSerializedForm(
	Activity activity
)
这一对方法对序列化的状态用GZIP进行了压缩，上面六十多KB的数据现在只有13K左右了。