SQLServer Error: 802, There is insufficient memory available in the buffer pool. [SQLSTATE 42000]

SQL Server Error 802 – Insufficient Memory Available in the Buffer Pool

The main reason behind getting SQL Server error 802 is your SQL Server instance is under memory pressure and there is not enough memory available to allocate further to buffer pool or buffer pool is restricted to not use memory beyond a certain limit. This might be because of various reasons as i have stated in below section. One of the very easy and straight forward approach to fix this error is to increase more memory to SQL Server system and modify max server memory in SQL Server accordingly.

Analysis & Solution

I would suggest to go deeper in this issue before taking any decision to allocate more memory to the system where SQL Server is running. There could be multiple temporary reasons as well which can cause SQL Server to generate below error log:

SQL Server Error: 802, There is insufficient memory available in the buffer pool. [SQLSTATE 42000]

Let’s discuss this issue further and ensure to not forget below points before taking any decisions.

Please comment us about your issue experience and let me know how you have fixed your issue.

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• Fix SQL Server Error 701: There is Insufficient System Memory to Run this Query

We can use Windows PerfMon utility to gather current values of all given performance counters. Just type perfmon in run prompt to launch perfmon tool to gather memory related performance counters. Although, Microsoft has also given a DMV related to performance counters that is very useful in collecting data and detecting CPU, IO or memory bottleneck in SQL Server. You can run below command to get all performance counters and their respective values using DMV sys.dm_os_performance_counters. You can also use this DMV to get performance counter values to identify memory pressure in SQL Server.

Select * from sys.dm_os_performance_counters

By default, SQL Server changes its memory requirements dynamically, on the basis of available system resources. I have explained SQL Server Memory Management and how SQL Server allocated memory to their transactions in below attached article.

• SQL Server Memory Allocation & Role of MIN/MAX Server Memory Configuration

Performance Counters to Identify SQL Server Memory Pressure

Let’s discuss top perfmon counters for memory usages to identify its bottleneck. Below is the list of top 10 performance counters to identify SQL Server Memory pressure. If you want to read CPU and Disk IO related perfmon counters then i would suggest you to read below attached articles.

• Top Perfmon Counters to Identify SQL Server CPU Bottleneck
• Identify Disk Bottleneck in SQL Server using Perfmon Disk Counters

Memory: Available Bytes

First thing you should look at in case of memory bottleneck in SQL Server is the available memory that can be used by processes. You can get this value by looking at the counter Available Bytes under object Memory. Low value of this counter shows the memory shortage on this server.  Now, you should focus behind the reason of this memory shortage. There might be possibility that some of your applications running on your server are not releasing memory or your system has not enough memory to perform current workload that leads to the memory bottleneck in SQL Server.

Memory: Pages/sec

This counter indicates the total number of pages that are either read from disk or written to the disk due to page fault. When a process requests a data page that is not in memory then it will be retrieved from disk to memory. This process is known is page fault. High value of this counter could indicate the excessive paging. We should further monitor Memory: Page Faults/sec counter to go indepth information. The average Pages/sec value should be below 50. A high value of Pages/sec indicates intensive memory activities like read from and write to disk. It means transactions are getting enough memory that is why they are using disk to process their requests.

Memory: Page Faults/sec

High value of counter Memory: Pages/sec could indicate the excessive paging. Next, we should monitor the Memory: Page Faults/sec counter to make sure that the disk activity is not caused by paging. If you want to determine whether SQL Server or another process is causing excessive paging then we should monitor the Process: Page Faults/sec counter for the SQL Server process instance. This will give an exact picture whether SQL Server is causing this paging issue or not.

Process: Working Set

This counter shows the amount of memory a process can use. This counter value shows whether you have set optimum value in min server memory and max server memory configuration or not. If this value shows constantly below min server memory and max server memory then you have configured too much memory for your SQL Server.

SQL Server: Buffer Manager: Buffer Cache Hit Ratio

This is very important counter and this counter shows the number of percentage that has been satisfied using data cache. Suppose the value of buffer cache hit ratio for your server is 94 it means 94% of total requests for data have been processed using data cache.

The ideal value for this counter is more than 90. Higher the value better the memory health.

SQL Server: Buffer Manager: Page Life Expectancy

Page Life Expectancy is very important counter to measure memory pressure for your system. THis counter indicates the average number of seconds a data page to remain in cache. Ideally, we have read multiple blogs to consider 300 or more as acceptable value but this value varies depending on your system configuration.

The ideal value is more than 300 but always compare this value with your system configuration. Higher the better concept is also applying here.

SQL Server: Buffer Manager: Free List Stalls/sec

This counter also shows a sign of memory pressure or insufficient memory on your server. This displays the number of requests per second where data requests stall because there are no buffers available. Any value greater than two indicates that SQL Server needs more memory.

SQL Server: Buffer Manager: Lazy Writes/sec

This counter tells about total number of Lazy writer performed in a second.  It means total number of times Lazy Writer process moves dirty pages from the buffer to disk. A lower number is better than a higher number. If value of this counter shows higher value continuously more than 20, then we need to add more memory to the system or we should think about optimizing memory intensive operations.

SQL Server: Buffer Manager: Checkpoint Pages/sec

This counter monitors the number of dirty pages per second, which are flushed to disk when SQL Server invokes the checkpoint process. High values for this counter may indicate memory pressure or insufficient memory.

SQL Server: Memory Manager: Memory Grants Pending

This counter shows the number of processes waiting for memory grant per second. Any value higher than zero indicates a lack of memory. We can also get this information by using a DMV sys.dm_exec_query_memory_grants. Those processes who are waiting to be granted the required memory will show you waiting with RESOURCE_SEMAPHORE wait type. I have explained about resource semaphore wait type in below attached article.

• Fix RESOURCE_SEMAPHORE Wait Type in SQL Server

Here, I have described top 10 performance counters to identify SQL Server memory pressure on your database server. I hope you like this article. Please follow our Facebook page and Twitter handle to get latest updates.

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• Fix Error 833: SQL Server has encountered 32 occurrences of I/O requests taking longer than 15 seconds to complete.
• Disk and Performance Impact of running Online Index Rebuild Operation
• Understanding ASYNC_IO_COMPLETION Wait Type

The post Top 10 Performance Counters to Identify SQL Server Memory Pressure appeared first on Techyaz.com.

Error 701, Severity: 17, State: 193.
There is insufficient system memory to run this query.

Or

Error 802, Severity: 17, State: 20
There is insufficient memory available in the buffer pool.

Error 701 or Error 802: Root Cause

If SQL Server is running out of memory and has no more memory available to allocate to its transactions then it will generate SQL Server memory error 701 or error 802. SQL Server Memory pressure or insufficient memory issue can be raised due to huge data load or other memory intensive operations.

We should check DBCC MEMORYSTATUS output to get latest snapshot of current memory status of the SQL Server. This command is very useful in troubleshooting memory issues in SQL Server. You might even have failed to run this DBCC command because system does not have enough memory. You need to reduce some memory pressure by stopping or killing some processes and then try to run this command to gather in depth information about SQL Server memory state.

The transaction that failed due to memory pressure and generates error 701 or error 802 might be or might not be the cause of this error. We should analyze the trends to reach on any conclusion.

Solution

There are mainly two reasons behind getting SQL Server memory issues for most of the SQL Server systems. Either your server has less memory to handle the current day to day workload or you are running some of the adhoc transactions that will require more memory for their execution like huge bulk data load, complex reports etc. If your SQL Server is running with insufficient memory during day to day activities then you should seriously evaluate the total workload and propose optimum memory size that can handle your current workload.

If you are planning to run any heavy ad hoc transaction then you should temporary increase the memory that can handle the transaction smoothly or you should run such transactions on a server that are built to handle such loads. You should also consider to reduce the batch size that is optimum for your system.

SQL Server is memory intensive application. We need to plan memory sizing for a server after proper evaluation of server state and overall load that will run on that SQL Server instance. But if you are facing memory issue on one of your SQL Server then first we need to troubleshoot it and find the root cause of this memory pressure. Here I am giving you step by step method to find the actual culprit that are causing the memory issue and possible solutions that can reduce some memory overheads.

First Make sure your SQL Server instance is running on dedicated server and not with other applications. If other applications are also using your database server then make sure they are not eating most of the memory. And, If most of the system memory is taken by other applications then you need to seriously think about migrating those application from this database server.

If you cannot migrate these applications to another server then workaround for such issues are to allocate the maximum memory value to your SQL Server instance. You can do it either by using sp_configure or using GUI. Read attached article to change max memory value for your SQL Server instance.

• Understanding SQL Server Memory Allocation and Role of MIN/MAX Server Memory Configuration

Next thing you should check is the server memory configuration. Check below SQL Server memory configuration parameters:

• max server memory
• min server memory
• min memory per query

Notice any unusual settings and fix them as necessary. All above three options have been covered in detain in above attached article.

Now, check the workload in terms of number of concurrent sessions, currently executing queries along with their memory grants. You should also focus on SQL Server transactions that are seeking huge memory values. Look at the transactions and gather a report for high memory intensive operations. Evaluate them and if possible optimize them so that they can take minimum memory.

• Understanding Memory Wait type Resource_SEMAPHORE and how to fix it?

You can also run below DBCC commands to free several SQL Server memory caches. This will also help you and make some relief for your current running transactions but in longer run it will not help if your system will need more memory to proceed the transactions.

• DBCC FREESYSTEMCACHE
• DBCC FREESESSIONCACHE
• DBCC FREEPROCCACHE

Another effective way to look in to memory status is by getting the output of DBCC MEMORYSTATUS command. You would get a good starting point to look in to culprit memory consumers.

We can also start collecting performance monitor counters for memory. Perfmon counters like the value of SQL Server: Buffer Manager\Buffer Cache Hit Ratio, SQL Server: Memory Manager and Page Life Expectancy will be very helpful in identifying memory pressure on SQL Server system. Analyze the trend for these counters and then decide whether issue is coming during some specific operations or system is continuously facing memory pressure.

Based on these analyses you can choose to either increase the system memory, increase the SQL Server memory allocation or reschedule some of the memory specific transactions to the off hours when load is minimum on the system. You can also reduce the batch size of the transaction to reduce the memory pressure. This will be certainly helpful in troubleshooting memory issues.

It is not necessary that your transactions are poorly designed always that is why SQL Server is taking lot of memory to process it. Sometimes even our systems on which SQL Server runs might have problem that end up with memory pressure. So you should consider all these points while fixing any performance issue.
I hope you like this article. Please follow us on our Facebook page and Twitter handle to get latest updates.

Read More:

• 4 Usages of DBCC SQLPERF in SQL Server
• Manage Transaction Log File during Bulk Data Load
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• Overview of SQL Server Performance Tuning
• Identify Disk Bottleneck in SQL Server using Perfmon Disk Counters

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RESOURCE_SEMAPHORE waits occurs when a query memory request cannot be granted immediately due to other concurrent queries. High waits and wait times may indicate excessive number of concurrent queries, or excessive memory request amounts.

High waits on RESOURCE_SEMAPHORE usually result in poor response times for all database users, and need to be addressed.

It is also useful to correlate high waits on RESOURCE_SEMAPHORE with the Memory Grants Pending and Memory Grants Outstanding SQL Memory Manager performance counters. Higher values for these counters indicate a definite memory problem especially a non-zero value for Memory Grants Pending.

Resource Semaphore is a SQL Server internal mechanism that allows a query to reserve memory only if there is enough free memory available otherwise, a requesting query is forced to wait in queue. When resource semaphore receives new request, it first checks if any query is waiting or not. If any query is waiting in queue then the new request will also be added to the queue based on first come first serve allocation. All these requests in queue will show you waiting with RESOURCE_SEMAPHORE wait type. Once enough memory will be available then memory will be granted to the requests in an order they have been queued.

The root cause of this type of memory problem is when memory-intensive queries, such as those involving sorting and hashing, are queued and are unable to obtain the requested memory. The solution would be to tune the offending queries, or manage their workload so that they are executed at less busy times.

SQL Server has provided few DMVs to identify and fix such memory issues. You can have a look at DMV sys.dm_exec_query_resource_semaphore that will show the current status of resource semaphore . You can also see the output of DMV sys.dm_exec_query_memory_grants to display all queries that have memory granted and those who are waiting to be granted the required memory. All waiting queries would have null value in grant_time column in the output of DMV sys.dm_exec_query_memory_grants.

You can get the queries that are causing or eating most of the memory using above DMVs and from here you can look at the options of optimizing the memory intensive statements. You can also have a look at below article if your system is facing insufficient memory issue.

• SQL Server Error 701 and Error 802: There is Insufficient System Memory to Run this Query
• Understanding SQL Server Memory Allocation and Role of MIN/MAX Server Memory Configuration

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Related Articles:

• Understanding SQL Server Wait Types
• How to Deal with ASYNC_IO_COMPLETION wait type?
• Understanding BACKUPBUFFER Wait type

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