我有一个非常慢的sql事务,它在表中插入新行。来自其他连接的所有其他“选择”查询等待此转换以解锁表。
在第一个事务有效时,是否可以从表中获取旧行?
SqlExpress 2008 R2。 对于exapmle:
private void button1_Click(object sender, EventArgs e)
{
System.Threading.Thread t = new System.Threading.Thread(
delegate()
{
var conn = new SqlConnection(@"Data Source=ARTNB\SQLEXPRESS;Initial Catalog=test;User ID=**;Password=******");
conn.Open();
var cmd = conn.CreateCommand();
var tr = conn.BeginTransaction( IsolationLevel.RepeatableRead, "test");
cmd.Transaction = tr;
cmd.CommandText = @"INSERT INTO Cards (SerialNumber,OperationID,TariffID,RequestTime,State,AgentInfo) VALUES('1213','345',13, GETDATE(),1,'')";
cmd.ExecuteNonQuery();
//very slow transaction
System.Threading.Thread.Sleep(300000);
tr.Commit();
conn.Close();
});
t.Start();
}
private void button2_Click(object sender, EventArgs e)
{
var conn = new SqlConnection(@"Data Source=ARTNB\SQLEXPRESS;Initial Catalog=test;User ID=**;Password=******");
conn.Open();
var cmd = conn.CreateCommand();
var tr = conn.BeginTransaction(IsolationLevel.RepeatableRead, "test2");
cmd.Transaction = tr;
cmd.CommandText = @"SELECT COUNT(*) FROM Cards";
var r = cmd.ExecuteReader();
r.Read();
r.Close();
tr.Commit();
conn.Close();
}
button2_Click方法不会立即获取行,它等待提交我有一个非常慢的sql事务,它在表中插入新行。来自其他连接的所有其他“选择”查询等待此转换以解锁表。
在第一个事务有效时,是否可以从表中获取旧行?
SqlExpress 2008 R2。 对于exapmle:
private void button1_Click(object sender, EventArgs e)
{
System.Threading.Thread t = new System.Threading.Thread(
delegate()
{
var conn = new SqlConnection(@"Data Source=ARTNB\SQLEXPRESS;Initial Catalog=test;User ID=**;Password=******");
conn.Open();
var cmd = conn.CreateCommand();
var tr = conn.BeginTransaction( IsolationLevel.RepeatableRead, "test");
cmd.Transaction = tr;
cmd.CommandText = @"INSERT INTO Cards (SerialNumber,OperationID,TariffID,RequestTime,State,AgentInfo) VALUES('1213','345',13, GETDATE(),1,'')";
cmd.ExecuteNonQuery();
//very slow transaction
System.Threading.Thread.Sleep(300000);
tr.Commit();
conn.Close();
});
t.Start();
}
private void button2_Click(object sender, EventArgs e)
{
var conn = new SqlConnection(@"Data Source=ARTNB\SQLEXPRESS;Initial Catalog=test;User ID=**;Password=******");
conn.Open();
var cmd = conn.CreateCommand();
var tr = conn.BeginTransaction(IsolationLevel.RepeatableRead, "test2");
cmd.Transaction = tr;
cmd.CommandText = @"SELECT COUNT(*) FROM Cards";
var r = cmd.ExecuteReader();
r.Read();
r.Close();
tr.Commit();
conn.Close();
}
button2_Click方法不会立即获取行,它会在button1_Click线程中等待提交。
答案 0 :(得分:4)
快速“退出监狱”卡是在数据库上启用读取已提交的快照,请参阅Choosing Row Versioning-based Isolation Levels中提到的Deadlocked!。当在数据库上启用RCSI时,你的butonn2点击读取将完全符合你的要求:它将读取行的旧版本,无需等待button1提交。
要启用RCSI,只需运行一次:
ALTER DATABASE [test] SET READ_COMMITTED_SNAPSHOT ON;
当然没有免费午餐:启用行版本控制将在tempdb IO和大小中发生成本。见Row Versioning Resource Usage。对于Express实例,不会产生可衡量的影响。