Occurs when a task is waiting on a latch for a buffer that is in an
I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.
In practice, this almost always happens due to large scans over big tables. It almost never happens in queries that use indexes efficiently.
If your query is like this:
Select * from <table> where <col1> = <value> order by <PrimaryKey>
, check that you have a composite index on
If you don't have one, then you'll need either a full
INDEX SCAN if the
PRIMARY KEY is chosen, or a
SORT if an index on
col1 is chosen.
Both of them are very disk
I/O consuming operations on large tables.