MongoDB Learning: Gridfs

Gridfs is a mechanism for storing a binary file in Mongodb. Gridfs is used to store and restore files that exceed the 16M(BSON file limit) ( e.g. pictures, audio, video, etc.) ).

There are several reasons for using Gridfs :

1 using Gridfs to simplify requirements

2 Gridfs will directly take advantage of the established replication or fragmentation mechanism, so it is easy to recover and extend for file storage

3 Gridfs can avoid some problems with the file system that is used to store user uploaded content. Gridfs will divide large file objects into smaller chunk ( file Fragments ), typically 256k/ , each chunk will be stored as a document of MongoDB chunks in the collection.

4 Gridfs does not produce disk fragmentation.

Here's how to use it:

Gridfs The most recent use of mongofiles command,mongofiles can be used to upload, download, display files in Gridfs.

(1) Create a new Test.txt Document

[Email protected]:/home/zhf# echo "Hello Mongod" > Test.txt

[Email protected]:/home/zhf# cat Test.txt

Hello Mongod

(2) through Mongofiles Upload

[Email protected]:/home/zhf# mongofiles put test.txt

2017-12-31t22:06:26.489+0800 Connected To:localhost

Added File:test.txt

(3) Show Files

[Email protected]:/home/zhf# mongofiles List

2017-12-31t22:06:41.308+0800 Connected To:localhost

Test.txt 13

(4) Delete the file on this side

[Email protected]:/home/zhf# rm test.txt

[Email protected]:/home/zhf# cat Test.txt

Cat:test.txt: no file or directory

(5) from Gridfs Download the file.

[Email protected]:/home/zhf# mongofiles Get test.txt

2017-12-31t22:07:43.762+0800 Connected To:localhost

Finished writing to Test.txt

[Email protected]:/home/zhf# cat Test,txt

Cat:test,txt: no file or directory

[Email protected]:/home/zhf# cat Test.txt

Hello Mongod

So Gridfs specifically how to store the file. The previous introduction to Gridfs is to solve the problem of single document cannot exceed 16M . Save the file by slicing it into a separate collection : Fs.chunks, and save a File index table:fs.files. In the previous example, we uploaded a test.txt file. We go into the database and see how it's stored.

The test Database is more in the database

> Show DBS

Admin 0.000GB

Local 0.000GB

Maple 0.000GB

Test 0.000GB

There are two sets of fs.chunks and fs.files under the test database .

> Use test

Switched to DB test

> Show Collections

Fs.chunks

Fs.files

The fields in the chunks are interpreted as follows:

_ID: Unique ID of the file

FILES_ID: The _id of the file document containing this block metadata

N: represents the block number. That is, the order number of the block in the original file. Here for 0 stands for only one block

Data: binary data that makes up a file block

> Db.fs.chunks.find ()

{"_id": ObjectId ("5a48eee22d33c14783a13d55"), "files_id": ObjectId ("5a48eee22d33c14783a13d54"), "n": 0, "Data": Binda TA (0, "agvsbg8gbw9uz29kcg==")}

The fields in files are explained as follows:

_ID: Unique ID in the file

Length: file Lengths

Chunksize: the size of each block. In bytes

Uploaddate: timestamp of file deposit Gridfs

MD5: MD5 checksum of the contents of the file . Generated by the server side.

> Db.fs.files.find ()

{"_id": ObjectId ("5a48eee22d33c14783a13d54"), "chunkSize": 261120, "uploaddate": Isodate ("2017-12-31t14:06:27.294z" ), "Length": +, "MD5": "40a1f080f26be5a4c8cef7d78f974659", "filename": "Test.txt"}

MongoDB Learning: Gridfs