当我们第二次运行相同 query 就会发现 physical reads 0. 因为之前的数据已经被缓存了 (除非我们跑上面的 clear cache command) 总结 physical reads 太多肯定就慢, 至于如何优化...我不知道, 看着办呗. Join and Loop Pattern 除了read row data, 连表也很讲究性能. SQL Server 有 3 种连表方式. 这3 种...
DBCC FREESYSTEMCACHE:清除系统缓存(请谨慎使用)。 类图 为了更好地理解 SQL Server 中的查询缓存及其结构,以下是对应的类图,使用mermaid语法构建的。 SQLServer+User+Database+QueryCache+ExecutionPlanUser+login()+executeQuery()Database+createTable()+insertData()QueryCache+addPlan()+removePlan()+clearCache()E...
SQLServer:Plan Cache < 70% 表示计划重用率低。 Buffer Cache Hit Ratio SQLServer:Buffer Manager < 97% 内存不足的潜在因素。 当CPU 的利用率很高时,还需要监视 SQL Server Lazy Writer(在 SQL Server 2000 中)或 Resource Monitor(在 SQL Server 2005 中)。通过称为 Resource Monitor 的资源线程刷新缓冲区...
Cache Hit Ratio:SQL Plans SQLServer:Plan Cache < 70% 表示计划重用率低。 Buffer Cache Hit Ratio SQLServer:Buffer Manager < 97% 内存不足的潜在因素。 当CPU 的利用率很高时,还需要监视 SQL Server Lazy Writer(在 SQL Server 2000 中)或 Resource Monitor(在 SQL Server 2005 中)。通过称为 Resource ...
使用SQL Server Management Studio 內建查詢存放區報表。 使用Azure 入口網站的 Azure SQL Database 查詢效能深入解析。 使用此sys.sp_query_store_set_hints及您想要套用至查詢的查詢提示字串來執行query_id。 此字串可包含一或多個查詢提示。 如需完整資訊, 請參閱sys.sp_query_store_set_hints。
The SQL Server Query Optimizer doesn't choose only the execution plan with the lowest resource cost; it chooses the plan that returns results to the user with a reasonable cost in resources and that returns the results the fastest. For example, processing a query in parallel typically uses ...
If a plan reuse for a batch happens, its compilation costs are avoided. Note that in the SQL Server literature, the word "procedure cache" has been used to describe what is called "plan cache" in this paper. "Plan cache" is more accurate because the plan cache stores query plans of ...
The query execution time is a summation of the query Executing CPU Time (Running) + Query Wait Time (Suspended) + Query Signal Wait Time (Runnable). It may be possible that a query goes to all these stats multiple times. In SQL Server the dynamic management view (DMV) “sys.dm_os_wai...
Clear the plan cache for all batches and stored procedures that access the table to refresh parameters encryption information. SQLCopy ALTERDATABASESCOPED CONFIGURATIONCLEARPROCEDURE_CACHE; Note If you don't remove the plan for the affected query from the cache, the first execution of the query af...
LATCH_*和内部cache的保护,这种等待过高会发生大量的问题。可以通过 sys.dm_os_latch_stats 查看详细内容。 ASYNC_NETWORK_IO 这个等待不完全表明网络的瓶颈。事实上多数情况下是客户端程序一行一行的处理sql server 的结果集导致。发生这种问题那么就修改客户端代码。