Native JSON support in MYSQL 5.7 : what are the pros and cons of JSON data type in MYSQL?

Question

In MySQL 5.7 a new data type for storing JSON data in MySQL tables has been added. It will obviously be a great change in MySQL. They listed some benefits

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Answer 1

From my experience, JSON implementation at least in MySql 5.7 is not very useful due to its poor performance. Well, it is not so bad for reading data and validation. However, JSON modification is 10-20 times slower with MySql that with Python or PHP. Lets imagine very simple JSON:

{ "name": "value" }

Lets suppose we have to convert it to something like that:

{ "name": "value", "newName": "value" }

You can create simple script with Python or PHP that will select all rows and update them one by one. You are not forced to make one huge transaction for it, so other applications will can use the table in parallel. Of course, you can also make one huge transaction if you want, so you'll get guarantee that MySql will perform "all or nothing", but other applications will most probably not be able to use database during transaction execution.

I have 40 millions rows table, and Python script updates it in 3-4 hours.

Now we have MySql JSON, so we don't need Python or PHP anymore, we can do something like that:

UPDATE `JsonTable` SET `JsonColumn` = JSON_SET(`JsonColumn`, "newName", JSON_EXTRACT(`JsonColumn`, "name"))

It looks simple and excellent. However, its speed is 10-20 times slower than Python version, and it is single transaction, so other applications can not modify the table data in parallel.

So, if we want to just duplicate JSON key in 40 millions rows table, we need to not use table at all during 30-40 hours. It has no sence.

About reading data, from my experience direct access to JSON field via JSON_EXTRACT in WHERE is also extremelly slow (much slower that TEXT with LIKE on not indexed column). Virtual generated columns perform much faster, however, if we know our data structure beforehand, we don't need JSON, we can use traditional columns instead. When we use JSON where it is really useful, i. e. when data structure is unknown or changes often (for example, custom plugin settings), virtual column creation on regular basis for any possible new columns doesn't look like good idea.

Python and PHP make JSON validation like a charm, so it is questionable do we need JSON validation on MySql side at all. Why not also validate XML, Microsoft Office documents or check spelling? ;)