Mongod config - WTCheck.tThread writes on disk into WiredTiger.wt every minute

Martin_Beran · 2021-01-26T19:54:59.599Z

I’ve installed mongodb 4.4.3 on my Raspberry Pi and I’ve noticed there are some IO operations even though no client is connected and no queries from my side.
First I’ve noticed FTDC writing every ~8seconds, so I set diagnosticDataCollectionEnabled: false . But there still remain writes into WiredTiger.wt (.turtle and index) every minute.
What does it do, is it some journal? Can I disable it?
It is my personal dev webserver, there won’t be much writing/reading from my side, so I dont see the point in mongo doing some unnecessary writing, since it will be just slowly killing my SSD.
(Btw. I’m a nub, never really worked with mongo)

My mongod.conf:

storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true

systemLog:
  destination: file
  logAppend: true
  path: /mnt/web/log/mongodb/mongod.log

net:
  port: 27017
  bindIp: 127.0.0.1

processManagement:
  timeZoneInfo: /usr/share/zoneinfo

security:
      authorization: "enabled"

setParameter:
  diagnosticDataCollectionEnabled: false

Martin_Beran · 2021-01-26T23:48:23.781Z

ok, after some digging I found out the one minute is storage.syncPeriodSecs, but I still have no idea why it is saving anything if there were no changes :-/ because I don’t think changing the syncPeriodSecs is the right way to fix it

Martin_Beran · 2021-01-27T19:40:58.513Z

seriously nobody knows? I have set storage.journal.enabled:false, the data are on binded external ssd, so I also set noatime and nodiratime… I checked iotop and it writes 40kB every minute, that would be 20.5GB a year for absolutely no reason

830 ?sys mongodb       0.00 B     40.00 K  0.00 %  0.00 % mongod --config /etc/mongod.conf [WTCheck.tThread]

I dont call any updates or inserts, the content of the WiredTiger.wt is still the same, why does it flush every minute then?
I’ve spent last 3 days googling and reading and I still have no clue why does it do that and nobody nowhere can tell me
I’m desperate and also really angry already

Marcus_Wang · 2024-02-10T13:31:12.877Z

Was this solved? I’m running mongod on a synology NAS/server and only write to the database, about, once per day. In the background, mongodb/WTCheck.tThread seems to write information out to disk every 60 seconds and I see the following getting logged to stdout at the same time.

“ctx”:“WTCheckpointThread”, “msg”:“WiredTiger message”

As a result my NAS never goes to sleep and is constantly writing or backing up those writes.

Marcus_Wang · 2024-02-10T16:03:10.074Z

In addition to diagnosticDataCollectionEnabled=false I’ve also added -nojournal and --quiet but still, every 60 seconds WTCheck insists on writing.