导读:1建站知识当日志文件在手动增长，自动增长和创建时都会进行填零初始化操作。但是请不要把这个过程和定期清除日志的过程高端网站建设网站seo优化培训。

误区 #14.清除日志后会将相关的LSN填零初始化

错误

当日志文件在手动增长，自动增长和创建时都会进行填零初始化操作。但是请不要把这个过程和定期清除日志的过程搞混。日志截断仅仅意味着将一个或多个VLF标记为不活动以便被重复使用。在日志清除的过程中，并没有任何日志被清除或是填0。“清除日志”和”截断日志”意思是一样的，但都属于用词不当，因为在这个过程中网站seo优化诊断工具日志的大小不会有任何改变。

你可以在我的博客中看到有关日志文件填零初始化的博文：Search Engine Q&A #24: Why can't the transaction log use instant initialization?。以及我发布在TechNet杂志的文章:Understanding Logging and Recovery in SQL Server。

你可以通过跟踪标记3004来查看SQL Server对日志文件进行填零初始化的过程。将这个追踪标记打开当日志文件增长时，你就可以在SQL Server日志中看到相关信息，下面是测试代码:

复制代码 代码如下:

DBCC TRACEON (3004, 3605); GO -- Create database and put in seo网站优化软件SIMPLE recovery model so the log 百度seo网站优化will clear on checkpoint CREATE DATABASE LogClearTest ON PRIMARY ( NAME = 'LogClearTest_data', FILENAME = N'D:\SQLskills\LogClearTest_data.mdf') LOG ON ( NAME = 'LogClearTest_log', FILENAME = N'D:\SQLskills\LogClearTest_log.ldf', SIZE = 20MB); GO -- Error log mark 1 ALTER DATABASE LogClearTest SET RECOVERY SIMPLE; GO USE LogClearTest; GO -- Create table and fill with 10MB - so 10MB in the log CREATE TABLE t1 (c1 INT IDENTITY, c2 CHAR (8000) DEFAULT 'a'); GO INSERT INTO t1 DEFAULT VALUES; GO 1280 -- Clear the log CHECKPOINT; GO -- Error log mark 2 ALTER DATABASE LogClearTest SET RECOVERY SIMPLE; GO

复制代码 代码如下:

2010-04-13 13:20:27.55 spid53 DBCC TRACEON 3004, server process ID (SPID) 53. This is an informational message only; no user action is required. 2010-04-13 13:20:27.55 spid53 DBCC TRACEON 3605, server process ID (SPID) 53. This is an informational message only; no user action is required. 2010-04-13 13:20:27.63 spid53 Zeroing D:\SQLskills\LogClearTest_log.ldf from page 0 to 2560 (0x0 to 0x1400000) 2010-04-13 13:20:28.01 spid53 Zeroing completed on D:\SQLskills\LogClearTest_log.ldf 2010-04-13 13:20:28.11 spid53 Starting up database 'LogClearTest'. 2010-04-13 13:20:28.12 spid53 FixupLogTail() zeroing D:\SQLskills\LogClearTest_log.ldf from 0x5000 to 0x6000. 2010-04-13 13:20:28.12 spid53 Zeroing D:\SQLskills\LogClearTest_log.ldf from page 3 to 63 (0x6000 to 0x7e000) 2010-04-13 13:20:28.14 spid53 Zeroing completed on D:\SQLskills\LogClearTest_log.ldf 2010-04-13 13:20:28.16 spid53 Setting database option RECOVERY to SIMPLE for database LogClearTest. 2010-04-13 13:20:29.49 spid53 Setting database option RECOVERY to SIMPLE for database LogClearTest.

关键词标签: 误区 SQL 会将