As with any database platform, MongoDB performance is of paramount importance to keeping your application running quickly. In this blog post, we’ll show you five configuration options that can impact the performance for your MongoDB Deployment and will help keep your database fast and performing at its peak.
MongoDB Performance Overview
MongoDB performance consists of several factors; there’s OS Settings, DB Configuration Settings, DB Internal Settings, Memory Settings, and Application Settings. This post is going to focus on the MongoDB database configuration options around performance and how to set them. These options are ones that are set in the database configuration itself that can impact your performance.
Configuration Options
So how do we ensure our performance configuration options are enabled or set up correctly? And which ones are the most important? We’ll now go through five configuration options that will help your MongoDB environment be performant!
MongoDB uses a configuration file in the YAML file format. The configuration file is usually found in the following locations, depending on your Operating System:
DEFAULT CONFIGURATION FILE
- On Linux, a default /etc/mongod.conf configuration file is included when using a package manager to install MongoDB.
- On Windows, a default <install directory>/bin/mongod.cfg configuration file is included during the installation.
- On macOS, a default /usr/local/etc/mongod.conf configuration file is included when installing from MongoDB’s official Homebrew tap.
storage.wiredTiger.engineConfig.cacheSizeGB
Our first configuration option to help with your MongoDB performance is storage.wiredTiger.engineConfig.cacheSizeGB.
|
1 2 3 4 |
storage: wiredTiger: engineConfig: cacheSizeGB: <value> |
Since MongoDB 3.0, MongoDB has used WiredTiger as its default Storage Engine, so we’ll be examining MongoDB Memory Performance from a WiredTiger perspective. By default, MongoDB will reserve 50% of the available memory – 1 GB for the WiredTiger cache or 256 MB, whichever is greater. For example, a system with 16 GB of RAM would have a WiredTiger cache size of 7.5 GB.
|
1 |
( 0.5 * (16-1) ) |
The size of this cache is important to ensure WiredTiger is performant. It’s worth taking a look to see if you should alter it from the default. A good rule of thumb is that the size of the cache should be large enough to hold the entire application working set.
Note that if you’re in a containerized environment, you may also need to set the configuration option to 50% – 1 GB of the memory that is available to the container. MongoDB may adhere to the container’s memory limits or it may get the host’s memory limit, depending on how the system call is returned when MongoDB asks. You can verify what MongoDB believes the memory limit is by running:
|
1 |
db.hostInfo() |
And checking the hostinfo.system.memLimitMB value. This is available from MongoDB 3.6.13+ and MongoDB 4.0.9+ forward.
How do we know whether to increase or decrease our cache size? Look at the cache usage statistics:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 |
db.serverStatus().wiredTiger.cache { "application threads page read from disk to cache count" : 9, "application threads page read from disk to cache time (usecs)" : 17555, "application threads page write from cache to disk count" : 1820, "application threads page write from cache to disk time (usecs)" : 1052322, "bytes allocated for updates" : 20043, "bytes belonging to page images in the cache" : 46742, "bytes belonging to the history store table in the cache" : 173, "bytes currently in the cache" : 73044, "bytes dirty in the cache cumulative" : 38638327, "bytes not belonging to page images in the cache" : 26302, "bytes read into cache" : 43280, "bytes written from cache" : 20517382, "cache overflow score" : 0, "checkpoint blocked page eviction" : 0, "eviction calls to get a page" : 5973, "eviction calls to get a page found queue empty" : 4973, "eviction calls to get a page found queue empty after locking" : 20, "eviction currently operating in aggressive mode" : 0, "eviction empty score" : 0, "eviction passes of a file" : 0, "eviction server candidate queue empty when topping up" : 0, "eviction server candidate queue not empty when topping up" : 0, "eviction server evicting pages" : 0, "eviction server slept, because we did not make progress with eviction" : 735, "eviction server unable to reach eviction goal" : 0, "eviction server waiting for a leaf page" : 2, "eviction state" : 64, "eviction walk target pages histogram - 0-9" : 0, "eviction walk target pages histogram - 10-31" : 0, "eviction walk target pages histogram - 128 and higher" : 0, "eviction walk target pages histogram - 32-63" : 0, "eviction walk target pages histogram - 64-128" : 0, "eviction walk target strategy both clean and dirty pages" : 0, "eviction walk target strategy only clean pages" : 0, "eviction walk target strategy only dirty pages" : 0, "eviction walks abandoned" : 0, "eviction walks gave up because they restarted their walk twice" : 0, "eviction walks gave up because they saw too many pages and found no candidates" : 0, "eviction walks gave up because they saw too many pages and found too few candidates" : 0, "eviction walks reached end of tree" : 0, "eviction walks started from root of tree" : 0, "eviction walks started from saved location in tree" : 0, "eviction worker thread active" : 4, "eviction worker thread created" : 0, "eviction worker thread evicting pages" : 902, "eviction worker thread removed" : 0, "eviction worker thread stable number" : 0, "files with active eviction walks" : 0, "files with new eviction walks started" : 0, "force re-tuning of eviction workers once in a while" : 0, "forced eviction - history store pages failed to evict while session has history store cursor open" : 0, "forced eviction - history store pages selected while session has history store cursor open" : 0, "forced eviction - history store pages successfully evicted while session has history store cursor open" : 0, "forced eviction - pages evicted that were clean count" : 0, "forced eviction - pages evicted that were clean time (usecs)" : 0, "forced eviction - pages evicted that were dirty count" : 0, "forced eviction - pages evicted that were dirty time (usecs)" : 0, "forced eviction - pages selected because of too many deleted items count" : 0, "forced eviction - pages selected count" : 0, "forced eviction - pages selected unable to be evicted count" : 0, "forced eviction - pages selected unable to be evicted time" : 0, "forced eviction - session returned rollback error while force evicting due to being oldest" : 0, "hazard pointer blocked page eviction" : 0, "hazard pointer check calls" : 902, "hazard pointer check entries walked" : 25, "hazard pointer maximum array length" : 1, "history store key truncation calls that returned restart" : 0, "history store key truncation due to mixed timestamps" : 0, "history store key truncation due to the key being removed from the data page" : 0, "history store score" : 0, "history store table insert calls" : 0, "history store table insert calls that returned restart" : 0, "history store table max on-disk size" : 0, "history store table on-disk size" : 0, "history store table out-of-order resolved updates that lose their durable timestamp" : 0, "history store table out-of-order updates that were fixed up by moving existing records" : 0, "history store table out-of-order updates that were fixed up during insertion" : 0, "history store table reads" : 0, "history store table reads missed" : 0, "history store table reads requiring squashed modifies" : 0, "history store table remove calls due to key truncation" : 0, "history store table writes requiring squashed modifies" : 0, "in-memory page passed criteria to be split" : 0, "in-memory page splits" : 0, "internal pages evicted" : 0, "internal pages queued for eviction" : 0, "internal pages seen by eviction walk" : 0, "internal pages seen by eviction walk that are already queued" : 0, "internal pages split during eviction" : 0, "leaf pages split during eviction" : 0, "maximum bytes configured" : 8053063680, "maximum page size at eviction" : 376, "modified pages evicted" : 902, "modified pages evicted by application threads" : 0, "operations timed out waiting for space in cache" : 0, "overflow pages read into cache" : 0, "page split during eviction deepened the tree" : 0, "page written requiring history store records" : 0, "pages currently held in the cache" : 24, "pages evicted by application threads" : 0, "pages queued for eviction" : 0, "pages queued for eviction post lru sorting" : 0, "pages queued for urgent eviction" : 902, "pages queued for urgent eviction during walk" : 0, "pages read into cache" : 20, "pages read into cache after truncate" : 902, "pages read into cache after truncate in prepare state" : 0, "pages requested from the cache" : 33134, |