You can also log into mongo and repeat the two commands below (you need to execute both to update the output) to watch your memory usage spike as your server goes downhill. When MongoDB can no longer do that these warnings start showing up in /var/log/mongodb/mongod.log: T03:44:18.738+0000 I COMMAND serverStatus was very slow: That is the system function you call when you need to reserve memory for your machine. If you have even done C or C++ programming you will be familiar with malloc. You can also get memory usage statistics from MongoDB in the shell: db.serverStatus().mem At that point the system became unresponsive. Below you see that mongod is using 91% of the system’s memory in this example. VIRT and RES are virtual and resident memory. Of course you can use top -p (mongod pid) to monitor memory too. Total used free shared buff/cache available Divide the number shown by 1024*1024 to convert this number to gigabytes. Below is what my server looked like over 5 minute intervals when I ran the machine out of memory. To check your file system cache run free -k to show available virtual memory in kilobytes. That was used by the previous memory management module called MMAPv1. mapped-MongoDB since version 3.2 does not do memory mapping of files anymore.virtual-RAM plus memory that has extended to the file system cache, i.e.resident-amount of actual physical memory (RAM) used by a process.That’s a persistent URL as they assign a unique ID to your installation. You can see that on this 8GB machine it’s out of memory.This will cause MongoDB to send usage stats to their website where they will track those status and host it in a web page for you. Part of their web page looks likes like this. To use that, open the mongo shell and then paste in this command: db.enableFreeMonitoring() That’s hosted on their web site, but that does not mean you need to use their cloud service (Atlas). You should take advantage of the free monitoring service offered by MongoDB. So limiting it in one place will cut make it consume more in the other. But MongoDB uses both its internal cache and the system’s file system cache. You can limit the MongoDB cache size by adding the cacheSizeGB argument to the /etc/nf configuration file, as shown below. MongoDB, in its default configuration, will use will use the larger of either 256 MB or ½ of (ram – 1 GB) for its cache size. So people have reasoned that if your computer is running out of memory then you should limit the memory made available to MongoDB. In sum, the mongod process will consume more and more memory as it fills up its cache. There is much bad information on StackOverflow about what to do when your server runs out of memory. But it makes liberal use of cache, meaning data records kept memory for fast retrieval, as opposed to on disk. Although it can be configured to run that way. Use the right-hand menu to navigate.) When MongoDB Runs Out of Memory, Add Another Node (This article is part of our MongoDB Guide. Then we added 3.5 GB of data at which point it locked up when it reached 92% memory usage. Then we show what the logs looks like and what tools you can use to monitor this situation.Īt 215 MB of data this server consistently used 11% of memory when hitting it with multiple searches. We illustrate what a server looks when it runs out of memory by purposely adding more data to an 8 GB machine than it can support and then running queries against that. The solution to this is add another node to your cluster. It can do that quickly too, so quick that you will not even be able to shutdown the mongo db process as the bash shell will no longer respond. If you put too much data in your MongoDB database, it will run your server out of memory.
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