Why gridfs's chunk max size is 3.5*1000*1000? Can I increase it to 15*1000*1000?

[gavinliu]

Why gridfs's chunk max size is 3.5*1000*1000?
 Can I increase it to 15*1000*1000?
I want use chunk size = 8MB, this can decrease query times when download large files.

[Bernie Hackett]

The GridFS max chunk size is 16MB, just like the max document size in MongoDB.

>>> import gridfs

>>> gfs = gridfs.GridFS(db)

>>> file = 'x' * (32 * 1024 * 1024)

>>> len(file)

33554432

>>> gfs.put(file, chunkSize=15 * 1000 * 1000)

ObjectId('51b204d2fa5bd803b4c21ebd')

>>> db.fs.files.count()

1

>>> db.fs.chunks.count()

3

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[Sam Millman]

As for increasing the chunk size....It all depends, you need to see how it effects your working set.

[Bernie Hackett]

Let me clarify a little more. The max size of a "chunk" document is 16MB, like any other MongoDB document. There is some overhead for other required fields (see http://docs.mongodb.org/manual/reference/gridfs/#gridfs-chunks-collection). So the max chunk size is a bit less than 16MB.

[gavinliu]

Thanks a lot.
I find 3.5*1000*1000 in Java driver 2.9.1, and I don't understand why its limit is more small than document's max size(16MB).

[gavinliu]

In GridFS.java:  
 /**
     * file's chunk size
     */
    public static final int DEFAULT_CHUNKSIZE = 256 * 1024;

    /**
     * file's max chunk size
     */
    public static final long MAX_CHUNKSIZE = (long)(3.5 * 1000 * 1000);

[Bernie Hackett]

I don't know why that number was picked. It's not specified in the GridFS spec. You may want to open a ticket about it:

https://jira.mongodb.org/browse/JAVA

--

[gavinliu]

Yes, I will have a try. Thanks.