Flush Dirty bytes

[Prince_Das]

Hi Team ,

Thinking if we can manually flush “dirty bytes” from cache to disk .If yes , how can we do it ?
Help me in sharing documents link / commands.

Regards
Prince.

[Kobe_W]

There’s a lock side effect if you use fsync. Not sure if you want that.

This is the very first step before a disk snapshot based backup can be made.

[Kushagra_Kesav]

Hi @Prince_Das,

As @Kobe_W mentioned there is a way to do it using fsync but may I ask why you want to do that. Are you facing any issues related to it.

Best,
Kushagra

[Prince_Das]

@Kushagra_Kesav
No , i am not facing any issue , was thinking like in oracle if we want we can flush “dirty buffer” , without any issue ,… thought Mongodb might be having similar type of feature where we can flush those dirty bytes.

but not in regularly , Only if it reaches near to “bytes currently in the cache” . We can us those command …For temp. purpose.
@Kobe_W fsync would help but it can acquire locks .

Thanks both for the help.

Regards
Prince

[Kushagra_Kesav]

Hi @Prince_Das,

@Prince_Das

thought Mongodb might be having similar type of feature where we can flush those dirty bytes.

but not in regularly , Only if it reaches near to “bytes currently in the cache” . We can us those command …For temp. purpose.

In MongoDB, you don’t need to manually flush dirty bytes. The system takes care of automatically flushing them to disk once dirty contents in the WiredTiger cache reach 5%. It will flush them more aggressively once this number reaches 20% of the configured cache size. You can customize these numbers if you need more control, but unless you’re experiencing issues that can be conclusively traced to this setting, I would not recommend changing these values.

To read more, please refer to the WiredTiger: Cache and eviction tuning documentation.

Regards,
Kushagra