'How do I configure the cache size for Mongodb?

I need to handle cashing in Mongodb.Does It requires a lot of RAM for doing that? What are the specialties and advantages using storage engines in this case?

mongodbmmap


Solution 1:[1]

  1. Method (does not survive a restart):

    ./bin/mongo admin

    db.adminCommand( { "setParameter": 1, "wiredTigerEngineRuntimeConfig": "cache_size=10G"})

  2. start mongodb serve with

    ./bin/mongod --config server.conf --wiredTigerCacheSizeGB=10

--- server.conf (one key/value per line) ---

maxConns=200
logpath=logs/server.log
logappend=true
fork=true
dbpath=data
nohttpinterface=true
syncdelay=60
quiet = true
slowms = 2000
notablescan = false

Check size with this command:

> db.serverStatus().wiredTiger.cache
{
        "bytes currently in the cache" : 4606522365,
        "bytes read into cache" : 3291056,
        "bytes written from cache" : 5631783282,
        "checkpoint blocked page eviction" : 0,
        "eviction currently operating in aggressive mode" : 0,
        "eviction server candidate queue empty when topping up" : 448,
        "eviction server candidate queue not empty when topping up" : 0,
        "eviction server evicting pages" : 0,
        "eviction server populating queue, but not evicting pages" : 447,
        "eviction server unable to reach eviction goal" : 0,
        "eviction worker thread evicting pages" : 12,
        "failed eviction of pages that exceeded the in-memory maximum" : 0,
        "files with active eviction walks" : 0,
        "files with new eviction walks started" : 105,
        "hazard pointer blocked page eviction" : 0,
        "in-memory page passed criteria to be split" : 896,
        "in-memory page splits" : 448,
        "internal pages evicted" : 0,
        "internal pages split during eviction" : 0,
        "leaf pages split during eviction" : 13,
        "lookaside table insert calls" : 0,
        "lookaside table remove calls" : 0,
        "maximum bytes configured" : 10737418240,  <---- this is the configured size
        "maximum page size at eviction" : 8388576,
        "modified pages evicted" : 13,
        "modified pages evicted by application threads" : 0,
        "page split during eviction deepened the tree" : 0,
        "page written requiring lookaside records" : 0,
        "pages currently held in the cache" : 675,
        "pages evicted because they exceeded the in-memory maximum" : 1,
        "pages evicted because they had chains of deleted items" : 448,
        "pages evicted by application threads" : 0,
        "pages queued for eviction" : 12,
        "pages queued for urgent eviction" : 0,
        "pages read into cache" : 234,
        "pages read into cache requiring lookaside entries" : 0,
        "pages seen by eviction walk" : 25702,
        "pages selected for eviction unable to be evicted" : 0,
        "pages walked for eviction" : 127975,
        "pages written from cache" : 310352,
        "pages written requiring in-memory restoration" : 0,
        "percentage overhead" : 8,
        "tracked bytes belonging to internal pages in the cache" : 316858,
        "tracked bytes belonging to leaf pages in the cache" : 4606205507,
        "tracked bytes belonging to overflow pages in the cache" : 0,
        "tracked dirty bytes in the cache" : 809239633,
        "tracked dirty pages in the cache" : 190,
        "unmodified pages evicted" : 0
}

Solution 2:[2]

A more concise output of the WT cache size in GB would be :

db.serverStatus().wiredTiger.cache["maximum bytes configured"]/1024/1024/1024 64

Solution 3:[3]

Dba is the appropriate place. Caching is already defined if you are using WiredTiger, using all RAM available, with dynamic provisioning.

Solution 4:[4]

I had the same problem, and I got the answer. Take a look at this answer.

I hope your problem is solved too.

Summary answer :)

You need to add these configurations to docker-campus configurations:

.......
        deploy:
        resources:
            limits:
              memory: 3G
            reservations:
              memory: 1G
    command: --wiredTigerCacheSizeGB 0.25
    
.......

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Literadix
Solution 2 Alex Man
Solution 3 Ricardo Barros Lourenço
Solution 4 torham

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