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EC

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Description:

This wait type went into disuse before SQL Server 2014, when it was re-purposed as the wait type that occurs when a page is being read from a buffer pool extension file.

(Books Online description: “Identified for informational purposes only. Not supported. Future compatibility is not guaranteed.”)

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Added in SQL Server version:

Pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 182 in 2008 and 2008 R2, and 186 in 2012 and 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

If this wait type is prevalent, that indicates that a large number of buffer pool extension reads are occurring. This may or may not be a performance issue, depending on the type of queries that are leading to BPE reads, as a BPE read is one page at a time. Single-threaded (or low degree of parallelism) scans will be most affected by having data in the BPE, and performance of these queries can be improved by using a higher degree of parallelism or removing the BPE.

Known occurrences in SQL Server (list number matches call stack list):

  1. Waiting for a page to be read from the buffer pool extension (in this case, while reading rows from a table)

And other similar call stacks.

Abbreviated call stacks (list number matches known occurrences list):

  1. SOS_Task::PostWait+0x9e
    EventInternal<SuspendQueueSLock>::Wait+0x2ca
    BPool::Map+0x47a
    BPool::LatchAndMap+0x98
    BPool::Get+0xd2
    IndexPageManager::GetNextPage+0x432
    IndexRowScanner::MoveKeyOrderToRowOnNextPage+0x16c
    IndexRowScanner::MoveToRowOnNextPage+0x23b
    IndexDataSetSession::GetNextRowValuesInternal+0x108b
    RowsetNewSS::GetNextRows+0xb7
    CQScanTableScanNew::GetRow+0x14d
    CQScanStreamAggregateNew::GetRowHelper+0x22c
    CQScanStreamAggregateNew::GetCalculatedRow+0x21
    CQScanNew::OpenHelper+0x41
    CQScanXProducerNew::Open+0xc8
    FnProducerOpen+0x44
    FnProducerThread+0x8c3
    SubprocEntrypoint+0xa7f
    SOS_Task::Param::Execute+0x21e
    SOS_Scheduler::RunTask+0xab