Mongodb version 3+ filestructure is different to previous versions

[LynnyK]

Hi,

I have Mongodb 2.6 version installed on server and the physical file for each database consists of

databasename.0

databasename.1

databasename.2 ...

and 1 .ns file

databasename.ns

I've now got another database server with 3.2 installed and noticed the filestructure is completely different.

The files i can see are a bunch of collection-nn-nnnnnnnnnnnnnnnn.wt and index-nn-nnnnnnnnnnnnnnnnnnnnnn.wt files.

In the earlier versions, if I wanted to copy the a database from one server to the other, I can just copy the files named with the same name, not so with version 3.

Is there a configuration or parameter to set so that the filestructure contained by database??

Does anyone understand the underlying file structure who can help me?

Thanks

Lyn

[Kevin Adistambha]

Hi Lyn,

I have Mongodb 2.6 version installed on server and the physical file for each database consists of
databasename.0
databasename.1

databasename.2 …

and 1 .ns file
databasename.ns

These are MMAPv1 physical files. The MMAPv1 storage engine was the default (and only) storage engine for MongoDB version 2.6.x.

I’ve now got another database server with 3.2 installed and noticed the filestructure is completely different.
The files i can see are a bunch of collection-nn-nnnnnnnnnnnnnnnn.wt and index-nn-nnnnnnnnnnnnnnnnnnnnnn.wt files.

These are WiredTiger physical files, which is currently (as per MongoDB version 3.2.x) the default storage engine employed by MongoDB.

Is there a configuration or parameter to set so that the filestructure contained by database??

No. The file structure is determined by the selected database storage engine and cannot be changed. I would also strongly discourage copying individual files between dbpath (especially on a running mongod instance) as this will likely introduce data corruption.

If you need to copy one database to another server, you might want to take a look at the db.copyDatabase() command instead.

Also, there are many advantages of using WiredTiger compared to MMAPv1, such as:

• Document level concurrency
• Better multithreaded performance
• Compression
• MultiVersion Concurrency Control to ensure data consistency

Unless you have a very specific need for MMAPv1 features, I would recommend you to use the WiredTiger storage engine instead due to WiredTiger’s generally better performance, concurrency abilities, and compression capabilities. Also, MMAPv1 files may be larger compared to the actual data size, due to storage padding and fragmentation.

Best regards,
Kevin

​

[Lyn Ko]

Thanks Kevin for taking time to reply

I also found the Config setting storage.directoryPerDB...was able to group all the files per db using this which was good

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