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Description:
Exactly as the Books Online description describes. This wait type was added so you can see how long a synchronous statistics update takes. Note that this is a preemptive wait, so the thread continues executing on the processor until the statistics update is complete.
(Books Online description: “Occurs when waiting for synchronous statistics update to complete before query compilation and execution can resume.”)
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Added in SQL Server version:
2019
Removed in SQL Server version:
N/A
Extended Events wait_type value:
The map_key value in sys.dm_xe_map_values is 1329 in 2019 RTM. You must check the DMV to get the latest value as some map_key values have changed in later builds.
Other information:
How long a query will have to wait for a synchronous statistics update to complete before it can compile and execute, depends on things like:
- How many tables in the query have statistics that need to be refreshed
- How many statistics have to be refreshed on each table
- The number of rows in each table
- The options specified when creating the statistic (e.g. FULLSCAN)
This delay is likely to be more problematic for queries involving very large, volatile tables.
Ways to eliminate or reduce this delay:
- Enable asynchronous statistics updates
- Disable any automatic statistics updates and perform your own regular statistics maintenance
- Avoid using the FULLSCAN option on statistics on large tables
Known occurrences in SQL Server (list number matches call stack list):
- 1-3 – various examples of this wait occurring while the actual statistics update occurs.
And many other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PopWait+0xf7
SOS_ExternalAutoWait::~SOS_ExternalAutoWait+0x5f
CTableMetadata::UpdateStatistics+0x501
CTableMetadata::StatsRefresh+0x40f
CTableMetadata::PStatManUpdateAndLoad+0x3e
CTableMetadata::PdstrhstLoadHistogram+0xd2
CGlobalHistogramCache::PdstrhstLoad+0x28e
CStCollBaseTable::PdstrhstGetHistogramInternal+0x4b3
CStCollAbstractLeaf::FCardDistinctSingleColumn+0x18f
CStCollAbstractLeaf::CardDistinctImpl+0x587
IStatsCollection::CardDistinct+0xbd
CStCollFilter::CardDistinctImpl+0x101
IStatsCollection::CardDistinct+0xbd
CStCollJoin::CardDistinct_OneSided+0x1f9
CStCollOuterJoin::CardDistinctImpl+0x1ea
IStatsCollection::CardDistinct+0xbd
CSelCalcSimpleJoinWithDistinctCounts::FCalculate+0x1b3
CCardUtilSQL12::ProbCalculateJoin+0x2bf
CLogOp_BaseJoin::PstcollDeriveCardinality+0x5ce
CCardFrameworkSQL12::DeriveCardinalityProperties+0x41d
CLogOpArg::DeriveGroupProperties+0xd93
COpArg::DeriveNormalizedGroupProperties+0x24e - SOS_Task::PopWait+0xf7
SOS_ExternalAutoWait::~SOS_ExternalAutoWait+0x5f
CTableMetadata::UpdateStatistics+0x501
CTableMetadata::StatsRefresh+0x40f
CTableMetadata::PStatManUpdateAndLoad+0x3e
CTableMetadata::PdstrhstLoadHistogram+0xd2
CGlobalHistogramCache::PdstrhstLoad+0x28e
CStCollBaseTable::PdstrhstGetHistogramInternal+0x4b3
CStCollAbstractLeaf::PdstrhstGetHistogram+0x1b
CSelCalcColumnInInterval::PdstrhstLoad+0x33a
CSelCalcColumnInInterval::FCalculate+0xb1
CSelCalcCombineFilters::FCalculate+0x9d
CCardUtilSQL12::ProbCalculateFilter+0x193
CLogOp_Select::PstcollDeriveCardinality+0x27c
CCardFrameworkSQL12::DeriveCardinalityProperties+0x41d
CLogOpArg::DeriveGroupProperties+0xd93
COpArg::DeriveNormalizedGroupProperties+0x24e
COptExpr::DeriveGroupProperties+0x15b - SOS_Task::PopWait+0xf7
SOS_ExternalAutoWait::~SOS_ExternalAutoWait+0x5f
CTableMetadata::UpdateStatistics+0x501
CTableMetadata::StatsRefresh+0x40f
CTableMetadata::PStatManUpdateAndLoad+0x3e
CTableMetadata::PdstrhstLoadHistogram+0xd2
CGlobalHistogramCache::PdstrhstLoad+0x28e
CStCollBaseTable::PdstrhstGetHistogramInternal+0x4b3
CStCollAbstractLeaf::PdstrhstGetHistogram+0x1b
CStCollFilter::PdstrhstGetHistogram+0x16b
CScalarStatsInfo::PdstrhstGetInputHistogramByPvr+0x9b
CScalarStatsInfo::PdstrhstCreateHistogram+0x63
CCardUtilSQL12::FGetHistogramsForFunctionComparisonJoin+0x1fd
CSelCalcExpressionComparedToExpression::FCalculate+0x189
CCardUtilSQL12::ProbCalculateJoin+0x2bf
CLogOp_BaseJoin::PstcollDeriveCardinality+0x5ce
CCardFrameworkSQL12::DeriveCardinalityProperties+0x41d
CLogOpArg::DeriveGroupProperties+0xd93
COpArg::DeriveNormalizedGroupProperties+0x24e
COptExpr::DeriveGroupProperties+0x15b