What level of CPU usage should be considered high for SQL Server? ie 80% 90% 100%?
if under normal loads the CPU averages above 40% I start to get nervous. However, that's because I know the nature of our traffic and the spikes we get. Your mileage may vary.
We actually aim even lower, for about a 7-10% average, but we do sometimes get processing that will spike us to 60%.
We measure total CPU every 30 seconds and email a report daily, and if we see a move of 2% away from that average we expect for that day we investigate.
It takes time but it's helps me sleep better at night :)
Generally, you don't want a machine to sustain a constant CPU of over 40 or 50%, because it won't be able to handle spikes in activity.
It really depends on your machine. The best thing is to monitor the server using perfmon and see when things start to run slowly. It is normal for SQL to use a lot of CPU under load.
Related
From the beginning of our Flink project.
My cluster have suffered from low back-pressure because of heavy parsing code.
So I put monitoring script on the system which keep asking back-pressure status from the task manager. ( Which run every 20 seconds for getting the highest value and average )
By the way when I turn off the script running, I found increment of back pressure ratio become much less slower than when I using the script.
So is there any efficient way to get the back pressure status without losing performance ?
I don't believe requesting back-pressure every 20 seconds would have a major impact on your workflow's performance.
Separately, if you've got available CPU cycles, then increasing the parallelism of the function(s) doing the parsing would be the next thing to try, to improve throughput.
I have an application that I'd like to make more efficient - it isn't taxing any one resource enough that I can identify it as a bottleneck, so perhaps the app is doing something that is preventing full efficiency.
The application pulls data from a database on one SQL Server instance, does some manipulation on it, then writes it to a database on another SQL Server instance - all on one machine. It doesn't do anything in parallel.
While the app is running (it can take several hours), none of the 4 CPU cores are maxed out (they hover around 40-60% utilization each), the disks are almost idle and very little RAM is used.
Reported values:
Target SQL Server instance: ~10% CPU utilization, 1.3GB RAM
Source SQL Server instance: ~10% CPU utilization, 300MB RAM
Application: ~6% CPU utilization, 45MB RAM
All the work is happening on one disk, which writes around 100KB/s during the operation, on average. 'Active time' according to task manager is usually 0%, occasionally flickering up to between 1 and 5% for a second or so. Average response time, again according to task manager, moves betweeen 0ms and 20ms, mainly showing between 0.5 and 2ms.
Databases are notorious for IO limitations. Now, seriously, as you say:
The application pulls data from a database on one SQL Server instance,
does some manipulation on it, then writes it to a database on another
SQL Server instance - all on one machine.
I somehow get the idea this is a end user level mashine, maybe a workstation. Your linear code (a bad idea to get full utilization btw, as you never run all 3 parts - read, process, write - in parallel) will be seriously limited by whatever IO subsystem you have.
But that will not come into play as long as you can state:
It doesn't do anything in parallel.
What it must do is do things in parallel:
One task is reading the next data
One task does the data processing
One task does the data writing
You can definitely max out a lot more than your 4 cores. Last time I did something like that (read / manipulate / write) we were maxing out 48 cores with around 96 or so processing threads running in parallel (and a smaller amount doing the writes). But a core of that is that your application msut start actually using multiple CPU's.
If you do not parallelize:
You only will max out one core max,
YOu basically waste time waiting for databases on both ends. The latency while you wait for data to be read or committed is latency you are not processing anything.
;) And once you fix that you will get IO problems. Promised.
I recommend reading How to analyse SQL Server performance. You need to capture and analyze the wait stats. These will tell you what is the execution doing that prevents it from going max out on CPU. You already have a feeling that the workload is causing the SQL engine to wait rather than run, but only after you understand the wait stats you'll be able to get a feel what is waiting for. Follow the article linked for specific analysis techniques.
Is there some way to monitor the CPU usage of a MS-SQL process and if it rises above a certain treshold, log the queries which get executed while the CPU usage is above the treshold?
Basically, the problem that I am having is that one of my databases becomes really slow regularly - several times a day. During the periods when the database is slow, the CPU usage of the SQL process is around the 90%- 100% and all the queries are timing out.
I am currently looking into ways to develop a small application to do that monitoring for me using .NET, but I thought that there might already be something existing for that.
Try sqlmonitor from redgate.
Its quite good at answering questions like "Usually everything works nice, but at a certain point in time something goes wrong".
We have an SQL server with about 40 different (about 1-5GB each) databases. The server is an 8 core 2.3G CPU with 32Gigs of RAM. 27Gig is pinned to SQL Server. The CPU utliziation is mostly close to 100% always and memory consumption is about 95%. The problem here is the CPU which is constantly close to 100% and trying to understand the reason.
I have run an initial check to see which database contributes to high CPU by using - this script but I could not substantiate in detail on whats really consuming CPU. The top query (from all DBs) only takes about 4 seconds to complete. IO is also not a bottleneck.
Would Memory be the culprit here? I have checked the memory split and the OBJECT CACHE occupies about 80% of memory allocated (27G) to SQL Server. I hope that is normal provided there are lot of SPs involved. Running profiler, I do see lot of recompiles, but mostly are due to "temp table changed", "deferred compile" etc and am not clear if these recompiles are a result of plans getting thrown out of cache due to memory pressure
Appreciate any thoughts.
You can see some reports in SSMS:
Right-click the instance name / reports / standard / top sessions
You can see top CPU consuming sessions. This may shed some light on what SQL processes are using resources. There are a few other CPU related reports if you look around. I was going to point to some more DMVs but if you've looked into that already I'll skip it.
You can use sp_BlitzCache to find the top CPU consuming queries. You can also sort by IO and other things as well. This is using DMV info which accumulates between restarts.
This article looks promising.
Some stackoverflow goodness from Mr. Ozar.
edit:
A little more advice...
A query running for 'only' 5 seconds can be a problem. It could be using all your cores and really running 8 cores times 5 seconds - 40 seconds of 'virtual' time. I like to use some DMVs to see how many executions have happened for that code to see what that 5 seconds adds up to.
According to this article on sqlserverstudymaterial;
Remember that "%Privileged time" is not based on 100%.It is based on number of processors.If you see 200 for sqlserver.exe and the system has 8 CPU then CPU consumed by sqlserver.exe is 200 out of 800 (only 25%).
If "% Privileged Time" value is more than 30% then it's generally caused by faulty drivers or anti-virus software. In such situations make sure the BIOS and filter drives are up to date and then try disabling the anti-virus software temporarily to see the change.
If "% User Time" is high then there is something consuming of SQL Server.
There are several known patterns which can be caused high CPU for processes running in SQL Server including
I recently finished my app and have since began testing. One of my
main resources makes 14 RPCs, I have made every effort to decrease CPU
time, i.e., marking properties as unindexed, however I really cannot
reduce the number of GETs, PUTs and queries that occur in the request.
The average CPU times associated with the request today is:
ms=381 cpu_ms=1192 api_cpu_ms=1122 cpm_usd=0.033597
This does fluctuate and can be less, however it rarely falls low
enough to have the high CPU warnings removed.
I've noticed my app still scales fine, I have about 15 instances
running whilst testing.
So my question is, should I be concerned at the high CPU warnings or
is it something most people experience?
As long as your wallclock time (the first time in those timings) averages less than 1000ms, your app will continue to autoscale just fine, regardless of how many CPU ms your app uses. As systempuntoout explains, the high CPU warnings are a holdover from when we limited high CPU requests on a per-url basis, and no longer apply except as a guide for optimisation.
If your application can't be optimized but the CPU usage is fine for your daily budget, I think you could ignore this warning without any concern.
Years ago, the number of High CPU Requests in a specific time was limited and the warning was useful to monitor and correct the application to stay above that specific quota; that limit was then removed and the High CPU warning is now useful just to identify part of the program that should be checked for optimization (where possible).
In practice, I've never had an issue with not enough instances being spun up to handle user requests even if I am running many longer-running jobs in the background [e.g., an expensive mapreduce job]. Of course, your budget needs to cover your CPU expenses or your app won't be able to operate.
However, I remember reading in the docs that if the majority of your requests take a long time, then app engine might not spin up additional instances to handle requests. However, if the majority of your requests are served quickly, then a minority of long-running jobs shouldn't cause any problems. (Unfortunately, I can't find the article/docs with the specific guidance on longer running requests at the moment.)