[转]LATCH waittypes

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LATCH waittypes

A latch is a short-term lightweight synchronization object. The   following list describes the different types of latches:

• Non-buffer (Non-BUF) latch: The non-buffer latches provide synchronization services to in-memory data structures or provide re-entrancy protection for concurrency-sensitive code lines. These latches can be used for a variety of things, but they are not used to synchronize access to buffer pages.
• Buffer (BUF) latch: The buffer latches are used to synchronize access to BUF structures and their associated database pages. The typical buffer latching occurs during operations that require serialization on a buffer page, (during a page split or during the allocation of a new page, for example). These latches are not held for the duration of a transaction. These are indicated in the master.dbo.sysprocesses table by the PAGELATCH waittypes.
• IO latch: The IO latches are a subset of BUF latches that are used when the buffer and associated data page or the index page is in the middle of an IO operation. PAGEIOLATCH waittypes are used for disk-to-memory transfers and a significant waittime for these waittypes suggests disk I/O subsystem issues.

Latch_X用于内部资源的同步

PageIOLatch_X用于将disk中的数据页同步到内存

PageLatch_X 用于内存中数据页的访问同步。

The following table lists the different latch waittypes that   you may notice in the master.dbo.sysprocesses system table in SQL Server 2000 and SQL Server 2005.

[转]LATCH waittypes

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原文地址：http://www.cnblogs.com/ljhdo/p/4916862.html