PAGELATCH_SH
Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Shared mode.
Detailed Description​
Latches are lightweight, fast methods of managing concurrency on a specific resource.
The PAGELATCH_* group of latches are seen in management of data pages that have already been read into memory.
PAGELATCH_SH is waiting for a latch to be allocated in shared (SH) mode so that a page can be read.
How to reduce this wait​
Waits on the PAGELATCH_* series of latches can be caused by hot pages in tables or indexes where the update or concurrency rate is very high, or due to pressure on TempDB.
Tempdb issues can be investigated using this article Breaking Down TempDB Contention
Using the the Microsoft white paper on Diagnosing and Resolving Latch Contention will help you find out what is going on and point your in the right direction to resolve your issue.
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