In SQL Server, a latch is a short-term lightweight synchronization object.

Buffer latches including wait type Pageiolatch_EX are used to synchronize access to BUF structures and associated pages in the SQL Server database. The most frequently occurring buffer latching situation is when serialization is required on a buffer page. These buffer latches are not held for the complete period of the transaction. The PAGEIO latches are a subset of BUF latches 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.

PAGEIOLATCH_EX (Exclusive mode page IO latch request)

When a SQL Server user needs a page that is not in buffer cache, the database must first allocate a buffer page, and then puts an exclusive PageIOLatch_ex latch on the buffer while the page is transferred from disk to cache. During this operation SQL Server puts a PageIOLatch_sh request on the buffer on behalf of the user. After the write to cache is complete, the PageIOLatch_ex latch is released.

Problem Indication

Excessive PageIOLatch_EX wait is an indication of disk subsystem problems.



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