SQL Server detects this condition Responding to the external and, depending on the memory pressure configuration, it might reduce the (SQL Server sets lower commit target of the buffer pool memory usage caps). and start clearing internal caches. Changed memory settings (for example, max server memory). Changes in memory distribution of internal components. Virtual Running low on available memory Running low on VAS (direct commitment (the difference allocations, DLLs loaded in between Memory:Commit Limit SQL Server VAS, high number of and Memory:Committed Bytes) threads) or VAS fragmentation (a is low (could be due to lack of lot of VAS is available but in small space in the system page files). blocks). This can cause the system to fail memory allocations. This condition SQL Server detects this condition can result in the whole system and can release reserved regions of responding very slowly or even VAS, reduce buffer pool commit bring it to a halt. target, and start shrinking caches. Windows has a notification mechanism that reports if physical memory is running high or low. SQL Server uses this mechanism in its memory management decisions. For more information, see in the Win32 and COM Development documentation in the MSDN Library. General troubleshooting steps in each case are explained in Table 3. Table 3 Pressure External Internal Physical Find major system memory Identify major memory consumers. consumers inside SQL Server. Attempt to eliminate (if possible). Verify server configuration. for adequate system Further actions depend on RAM and consider adding the investigation: for more RAM (usually requires workload; possible design more careful investigation issues; other resource beyond the scope of this bottlenecks. paper). Virtual Increase swap file size. Follow steps of internal physical memory pressure. Check for major physical memory consumers and follow steps of external physical memory pressure.
SQL Server detects this condition and, depending on the configuration, it might reduce the commit target of the buffer pool and start clearing internal caches. Responding to the external memory pressure (SQL Server sets lower memory usage caps). Changed memory settings (for example, max server memory). Changes in memory distribution of internal components. Virtual Running low on available memory commitment (the difference between Memory:Commit Limit and Memory:Committed Bytes) is low (could be due to lack of space in the system page files). This can cause the system to fail memory allocations. This condition can result in the whole system responding very slowly or even bring it to a halt. Running low on VAS (direct allocations, DLLs loaded in SQL Server VAS, high number of threads) or VAS fragmentation (a lot of VAS is available but in small blocks). SQL Server detects this condition and can release reserved regions of VAS, reduce buffer pool commit target, and start shrinking caches. Windows has a notification mechanism that reports if physical memory is running high or low. SQL Server uses this mechanism in its memory management decisions. For more information, see in the Win32 and COM Development documentation in the MSDN Library. General troubleshooting steps in each case are explained in Table 3. Table 3 Pressure External Internal Physical Find major system memory consumers. Attempt to eliminate (if possible). for adequate system RAM and consider adding more RAM (usually requires more careful investigation beyond the scope of this paper). Identify major memory consumers inside SQL Server. Verify server configuration. Further actions depend on the investigation: for workload; possible design issues; other resource bottlenecks. Virtual Increase swap file size. Check for major physical memory consumers and follow steps of external physical memory pressure. Follow steps of internal physical memory pressure.
TShootPerfProbs2008.docx