How Memory is being used

最新推荐文章于 2024-01-12 17:30:50 发布

echonul

最新推荐文章于 2024-01-12 17:30:50 发布

阅读量147

点赞数

CC 4.0 BY-SA版权

分类专栏： SQL Server 文章标签： Sql Server Memory

本文链接：https://blog.youkuaiyun.com/echonul/article/details/84510650

SQL Server 专栏收录该内容

6 篇文章

订阅专栏

本文介绍如何使用SQL Server的动态管理视图(dmvs)来检查和优化缓存中的查询计划及数据库缓冲池。通过具体SQL查询示例，展示了如何确定哪些查询最常被使用，以及哪些数据库对象消耗最多内存。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

To determine what plans are in the cache and how often they're used we can use sys.dm_os_memory_cache_counters dm view .

SELECT  TOP 6
 LEFT([name], 20) as [name],
 LEFT([type], 20) as [type],
 [single_pages_kb] + [multi_pages_kb] AS cache_kb,
 [entries_count]
FROM sys.dm_os_memory_cache_counters 
order by single_pages_kb + multi_pages_kb DESC

here :

CACHESTORE_OBJCP are compiled plans for stored procedures, functions and triggers.
CACHESTORE_SQLCP are cached SQL statements or batches that aren't in stored procedures, functions and triggers. This includes any dynamic SQL or raw SELECT statements sent to the server.
CACHESTORE_PHDR These are algebrizer trees for views, constraints and defaults. An algebrizer tree is the parsed SQL text that resolves the table and column names.

(you will find these counters in DBCC Memorystatus as well.Infact DBCC Memory Status uses this dm)

Generally you will find that CACHESTORE_SQLCP > CACHESTORE_OBJCP , but if the ratio of one to another is very high then we can say that there are more adhoc plans being run then Stored procedures.
That is the reason the sal statements are going in to Plan cache.

You can also monitor the number of data pages in the plan cache using Performance Monitor (PerfMon) using SQLServer:Plan Cache object with the Cache Pages counter. There are instances for SQL Plans (CACHESTORE_SQLCP), Object Plans (CACHESTORE_OBJCP) and Bound Trees (CACHESTORE_PHDR). This will give you the same picture ..for e.g. under bound tree : multiply cache pages by 8. you will get the same output as in dbcc memorystatus and the dm we used above.

After this to know the querry we can use sys.dm_exec_cached_plans and sys.dm_exec_sql_text dm views to find the queries

select  TOP 100
 objtype,
    usecounts, 
 p.size_in_bytes/1024 'IN KB',
 LEFT([sql].[text], 100) as [text]
from sys.dm_exec_cached_plans p
outer apply sys.dm_exec_sql_text (p.plan_handle) sql
ORDER BY usecounts DESC

Now , SQL Server memory is primarily used to store data (buffer) and query plans (cache).

We will try to find what tables and indexes are in the buffer memory of your server you can use sys.dm_os_buffer_descriptors DMV.

Further , the query below can give us total currrent size of buffer pool .

select count(*) AS Buffered_Page_Count
 ,count(*) * 8192 / (1024 * 1024) as Buffer_Pool_MB
from sys.dm_os_buffer_descriptors

After we have found the Bufferpool size , we can see which database is using more memory by runnig the query below .

SELECT LEFT(CASE database_id 
   WHEN 32767 THEN 'ResourceDb' 
   ELSE db_name(database_id) 
        END, 20) AS Database_Name,
 count(*)AS Buffered_Page_Count, 
 count(*) * 8192 / (1024 * 1024) as Buffer_Pool_MB
FROM sys.dm_os_buffer_descriptors
GROUP BY db_name(database_id) ,database_id
ORDER BY Buffered_Page_Count DESC

And then we can go further at object level to see what all objects are consuming memory (and how much) .We can use the query below in each database we wish to :

SELECT TOP 25 
 obj.[name],
 i.[name],
 i.[type_desc],
 count(*)AS Buffered_Page_Count ,
 count(*) * 8192 / (1024 * 1024) as Buffer_MB
    -- ,obj.name ,obj.index_id, i.[name]
FROM sys.dm_os_buffer_descriptors AS bd 
    INNER JOIN 
    (
        SELECT object_name(object_id) AS name 
            ,index_id ,allocation_unit_id, object_id
        FROM sys.allocation_units AS au
            INNER JOIN sys.partitions AS p 
                ON au.container_id = p.hobt_id 
                    AND (au.type = 1 OR au.type = 3)
        UNION ALL
        SELECT object_name(object_id) AS name   
            ,index_id, allocation_unit_id, object_id
        FROM sys.allocation_units AS au
            INNER JOIN sys.partitions AS p 
                ON au.container_id = p.hobt_id 
                    AND au.type = 2
    ) AS obj 
        ON bd.allocation_unit_id = obj.allocation_unit_id
LEFT JOIN sys.indexes i on i.object_id = obj.object_id AND i.index_id = obj.index_id
WHERE database_id = db_id()
GROUP BY obj.name, obj.index_id , i.[name],i.[type_desc]
ORDER BY Buffered_Page_Count DESC