SQL Server wait event pageiolatch_ EX

Time:2020-10-6

What is?PAGEIOLATCH_EXWaiting for events? Now we’re going toPAGEIOLATCH_EXWait for the relevant information of the event to do a simple summary, collation. aboutPAGEIOLATCH_EXThe official documents are as follows:

 

PAGEIOLATCH_EX

 

Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.

 

  Waiting on task I/O Occurs when a latch is requested for the buffer in the. Latch request inmonopolypattern. A long wait may indicate a problem with the disk subsystem.

 

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

Buffer latches including the PAGEIOLATCH_EX wait type 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 wait types are used for disk-to-memory transfers.

 

 

staySQL ServerIn, a latch is a transient lightweight synchronization object.

Buffer latch (includesPAGEIOLATCH_EXThe wait type is used for synchronous accessSQL Server In the database BUF Structure and associated pages. The most common buffer latch condition is when a serialization operation is required on a buffer page. These buffer latches do not remain unchanged for the entire duration of the transaction.PAGEIOA latch is a buffer and associated data page or index page in the IO Used in the middle of the operation BUFA subset of the latch.PAGEIOLATCH The wait type is 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_EX request on the buffer on behalf of the user. After the write to cache is complete, the PAGEIOLATCH_EX latch is released.

 

 

WhenSQL ServerWhen users need related pages that are not in the buffer cache, the database must first allocate a buffer page, and then place an exclusive on the buffer when the page is transferred from disk to cachePAGEIOLATCH_EXLatch. During this operation,SQL Server Issued on behalf of the user on the bufferPAGEIOLATCH_EXRequest. When the write cache is complete, it is releasedPAGEIOLATCH_EXLatch.

 

 

Problem indication

 

Excessive PAGEIOLATCH_EX waits occur when data is transfered from disk to memory for update operations and these transfers take time to complete.

This may be an indication of disk contention or other disk subsystem bottlenecks.

 

When data is transferred from disk to memory for update operation, a large number ofPAGEIOLATCH_EXWait, and these transfers (disksIOOperation) takes time to complete. This may indicate disk contention or other disk subsystem bottlenecks

 

PS: in fact, when a large number of data deletion operations occur in a large table, a large number ofPAGEIOLATCH_EXWait for the event.

 

 

 

Description:

 

This wait type is when a thread is waiting for the read of a data file page from disk to complete, and the thread is going to modify the page structure once it is in memory (EX = EXclusive mode). The Latches Whitepaper in the sidebar on the right has a description of all latch modes and their compatibility with other latch modes.

(Books Online description: “Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.”)

 

This type of waiting is that the thread is waiting for the completion of reading the relevant page of the data file from disk to memory, and once the thread will modify the page structure in memory(EX = EXclusiveMode). In the right sidebarLatch white paperDescribes all latch modes and their compatibility with other latch modes.

(online series Description:When the task is waitingI / OOccurs when the buffer in the request is latched. The latch request is in mutex mode. A long wait may indicate a problem with the disk subsystem.

 

 

 

 

PAGEIOLATCH_EX

 

A query is waiting for exclusive write access to a page in order to add data to the page, but the page is not currently in memory and has to be loaded from disk.

 

Page latches are lightweight, non-configurable locks used by internal processes within SQL Server to manage access to the page buffer in memory.  When SQL Server has to read pages from the disk into the memory buffer or from the buffer out to disk, it must place latches on the buffer pages while the processes take place.

It’s normal to see some PAGEIOLATCH_* waits, but if you’re frequently seeing them with wait times consistently above 10 milliseconds and you’re experiencing some type of latency, it suggests that the I/O subsystem is under pressure. Conversely, if you see many brief waits, you may be affected by increased I/O activity.

 

 

The query is waiting for exclusive write access to the page in order to add data to the page, but the page is not currently in memory and must be loaded from disk.

 

The latch isSQL Server Lightweight, non configurable locks used by internal processes to manage access to in memory page buffers. WhenSQL ServerWhen a page from the disk must be read to or from a memory buffer, it must place the latch on the buffer page while the process is in progress.

See somePAGEIOLATCH_ *It’s normal to wait, but if you see them often, the waiting time always exceeds10MS, and some type of delay is encounteredI/OThe subsystem is under pressure. On the contrary, if you see a lot of short waiting, you may be subject toI/OThe impact of increased activity.

 

 

 

 

reference material:

 

https://logicalread.com/2012/11/12/sql-server-pageiolatch_ex-wait-type/#.XkH2KCIzaHs

https://www.sqlskills.com/help/waits/pageiolatch_ex/

https://documentation.red-gate.com/sm4/working-with-overviews/using-performance-diagnostics/list-of-common-wait-types/pageiolatch_ex

https://docs.microsoft.com/zh-cn/sql/relational-databases/system-dynamic-management-views/sys-dm-os-wait-stats-transact-sql?redirectedfrom=MSDN&view=sql-server-ver15

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