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QDS_LOADDB Wait: Slow Startup and Query Store Load

June 10, 2020
Pinal Dave
SQL Performance
Query Store, SQL Server, SQL Wait Stats

A QDS_LOADDB wait means a database waits for Query Store to load its data at startup. This post reads the wait, checks the size of a store, explains the trace flag that loads Query Store asynchronously, and shows the settings that keep a store small.

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Metadata Contention in TempDB: When Memory-Optimized Metadata Helps

May 14, 2020
Pinal Dave
SQL Performance
In-Memory OLTP, SQL Memory, SQL TempDB, SQL Wait Stats

Metadata contention in TempDB happens when many sessions create and drop temporary tables at the same moment. This post reads the waits that point to it, explains why RESOURCE_SEMAPHORE is a different problem, and shows how SQL Server 2019 and later can keep that metadata in memory.

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Nonclustered Primary Key Test: Last Page Insert Waits

May 11, 2020
Pinal Dave
SQL Performance
Primary Key, SQL Constraint and Keys, SQL Identity, SQL Wait Stats, Testing

A nonclustered primary key test shows whether a heap fixes last page insert waits. On SQL Server 2025 it doesn’t, because the key index still rises. A lane layout that spreads the inserts removes the latch wait, and the post shows the cost of that layout.

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OPTIMIZE_FOR_SEQUENTIAL_KEY: Test the Last Page Insert Fix

May 6, 2020
Pinal Dave
SQL Performance
Primary Key, SQL Identity, SQL Server 2019, SQL Wait Stats, Testing

OPTIMIZE_FOR_SEQUENTIAL_KEY is an index option that targets last page insert contention. This post tests it with 32 connections that insert into a clustered identity key, with the option off and on. The option changes the kind of waiting, and the post shows how to decide whether it helps your table.

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SQL SERVER – Last Page Insert PAGELATCH_EX Contention Due to Identity Column

May 5, 2020
Pinal Dave
SQL Performance
Primary Key, SQL Constraint and Keys, SQL Identity, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Wait Stats, Testing

Today’s goal is to understand what is the Last Page Insert PAGELATCH_EX Contention Due to Primary Key. Let us start understanding it together.

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Recovery Model Insert Test: FULL vs SIMPLE Under Load

May 4, 2020
Pinal Dave
SQL Performance
Best Practices, SQL Backup and Restore, SQL Log, SQL Wait Stats, Testing

A recovery model insert test compares FULL and SIMPLE under a load of 16 connections. The log written is almost the same in both, and the elapsed time depends more on the server than on the model. The real difference is when the log can be reused, and this post shows that step by step.

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Insert Workload Waits: WRITELOG and PAGELATCH_EX

May 2, 2020
Pinal Dave
SQL Performance
Best Practices, SQL Log, SQL Scripts, SQL Wait Stats, Testing

Insert workload waits come down to two names, WRITELOG and PAGELATCH_EX. This post runs 16 connections that insert one row at a time and reads their waits with a tested script. It explains what each wait means and where to look for a fix.

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