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Ramesh Meyyappan’s SQL Server Performance Tuning Blog

Ramesh Meyyappan (www.sqlworkshops.com) is a SQL Server specialist with expertise in Performance Tuning. Ramesh worked at Microsoft Corporation from 1994 to 2004. Nearly half of that time he worked in Redmond in the development teams - specifically as Program Manager in the SQL Server Development Team responsible for optimizing SQL Server product for SAP. Ramesh now offers onsite and offsite consulting and workshops independently as well as by partnering with various Microsoft Subsidiaries. LinkedIn Profile: http://de.linkedin.com/in/rmeyyappan.

Tempdb Metadata Contention in SQL Server – Table Variable Vs Temporary Table

In SQL Server, the concurrent creation of temporary tables from many sessions can lead to tempdb metadata contention. Tempdb metadata contention does not affect the concurrent creation of table variables.

When SQL Server creates temporary tables, it has to update metadata information in the system based tables, like sys.sysschobjs (like… Read more

AlwaysOn Availability Groups Synchronous Replica Readable Secondary Data Access Latency

With SQL Server AlwaysOn Availability Groups, when you configure a secondary in synchronous-commit mode for read-only access, there can be data access latency.

If you make changes to your data like if you perform insert, update or delete in primary, those changes may not be visible in the secondary, synchronous… Read more

Seek or Scan – Cost Based Optimizer in SQL Server

When SQL Server has a choice of plans, it will compare the cost among a set of execution plans and will choose the cheapest one.

In some cases, even though the cost of seek is slightly higher than the cost of scan, SQL Server Optimize might still choose a seek… Read more

Optimize for Ad Hoc Workloads – SQL Server Configuration Parameter

SQL Server configuration parameter “optimized for ad hoc workloads” can be very useful when you execute lots of single use ad hoc statements or dynamic SQL statements by reducing memory usage of plan cache. If the majority of ad hoc statements or dynamic SQL statements execute more than once, then… Read more

Extended Event Locks Lock Waits in SQL Server

When it comes to lock waits, one of the important information we need to know is which statement waited for locks and how long. This is possible with extended events; it is not possible with SQL Server profiler.

locks_lock_waits event is very useful to find statements that waited for locks… Read more

Extended Event Query Post Execution Showplan in SQL Server

Query Post Execution Showplan event is a very useful event to find problematic queries and execution plans based on CPU usage or duration while analyzing performance issues.

It can increase the execution time of all queries by a fraction of a millisecond, irrespective of the total query cost, which means,… Read more

PAGELATCH Waits with Update Statements in SQL Server – PAGELATCH_EX and PAGELATCH_SH

In SQL Server, concurrent writes or read / write to the same page can lead to PAGELATCH (like PAGELATCH_EX and PAGELATCH_SH) waits or what is knowns as PAGELATCH contention.

One common use case is when invoice numbers are stored in a table. If the row is narrow, then many rows… Read more

Tempdb Allocation Contention in SQL Server

In SQL Server, the concurrent creation of temporary objects (temporary tables and table variables) from many sessions can lead to tempdb allocation contention. This contention occurs on PFS and SGAM pages in tempdb (like PAGELATCH_EX and PAGELATCH_SH waits). It is recommended to create additional data files for tempdb and implement… Read more

In-Memory OLTP Memory Optimized Table Variables Vs Disk Based Table Variable in SQL Server

Starting SQL Server 2014, it is possible to use memory optimized table variables. These are table variables declared using a table type which is memory optimized. Memory optimized table variables have no disk footprint and don’t have PAGELATCH (like PAGELATCH_EX and PAGELATCH_SH) or LOGBUFFER waits, hence they result in faster… Read more

Temp Table Caching in SQL Server

SQL Server caches temporary objects (temporary tables and table variables), that are created in a stored procedure. Temporary objects that are created either in dynamic SQL statement or by using sp_executesql are not cached. Temp table caching can lead to better performance by reducing Tempdb Allocation Contention. SQL Server… Read more

Filtered Statistics in SQL Server

In SQL Server, Filtered Statistics can improve cardinality estimation, i.e. when joining lookup table, or while joining fact table and dimension table. For this reason, SQL Server supports the creation of up to 30,000 statistics on non-indexed columns. Better estimation with filtered statistics can lead to faster query execution against… Read more

Parallel Insert Into – Table Variable Vs Temporary Table in SQL Server

In SQL Server, for insert into select statements, when the target for insert into is temporary table, the select statement can execute in parallel. When the target is table variable, SQL Server will not execute the select statement in parallel, which can lead to poor performance.

The below video demonstrates… Read more

Cardinality Estimation – Table Variable Vs Temporary Table in SQL Serve

SQL Server creates and maintains statistics for temporary tables, which lead to better cardinality estimation and optimal execution plan generation. Table variables have no statistics, which can result in poor cardinality estimation and non-optimal execution plan creation. When you add query hint option (recompile) when using table variable, SQL Server… Read more

Understanding ASYNC_NETWORK_IO Waits in SQL Server

In SQL Server, ASYNC_NETWORK_IO wait time can be high due to slow network, like when the database is in the cloud and the application is on premise. Furthermore, it can be slow when CPU utilization is high in the application server preventing timely fetching of all rows or, in most… Read more

Resource Governor in SQL Server – Workload Throttling

Resource Governor in SQL Server provides CPU, Memory and I/O throttling. In SQL Server 2014 and earlier, CPU throttling works only for similar kind of workloads and not for mixed workloads, where high importance workload group gets 9 slices of CPU, medium importance gets 3 slices and low 1 slice.… Read more

Data Compression in SQL Server – Pros and Cons

SQL Server supports row and page compression on tables, indexes and partitions. This can lead to reduced I/O and better performance. However, it can also result in additional CPU usage in some cases, outweighing the benefits of data compression. SQL Server query optimizer does not cost the overhead of expanding… Read more

SQL Server Command Timeout – Application Timeout – Attention

When you use ODBC or SqlClient to access data from SQL Server, by default the query will be cancelled if there is no response from the server within a certain period of time (30 seconds by default). ODBC or SqlClient will start a timer after sending the query to SQL… Read more

Slow performance due to SQL Server 2014 Buffer Pool Extension (BPE) and serial queries (MAXDOP 1)

The SQL Server 2014 Buffer Pool Extension feature can extend the buffer pool space on to Solid State Drive (SSD), where data and index pages can be cached. There is no possibility of data loss in the event of SSD failure as the cached data is clean (unmodified pages).

Buffer… Read more

NUMA remote (foreign) memory access overhead on Windows, SQL Server and In-Memory OLTP

In NUMA (Non-Uniform Memory Access), processors in the same physical location are grouped in a node which has its own local node memory. In a NUMA based system, there will be more than one such node and these nodes will use a shared interconnect mechanism to transfer data between them.… Read more

SQL Server 2012: Indirect Checkpoint (Target Recovery Time), get the real scoop

SQL Server 2012 brings a new feature called Indirect Checkpoint. You can read more about it here: http://msdn.microsoft.com/en-us/library/ms189573.aspx.

With Indirect Checkpoint, you get smaller and too many I/Os

Checkpoint normally writes large blocks of data to disk optimally in single write operation, up to 256KB, depending on the number… Read more

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