Max JSON column length in MySQL

Question

What's the max number of characters I can store in a JSON column in MySQL? I don't see this mentioned in the MySQL manual.

Answer 1

Here's a demo of what @JorgeLondoño is talking about.

Set the server's max allowed packet size:

mysql> set global max_allowed_packet=1024*1024*1024; 

Exit and open the mysql client again, this time setting the client max packet size to match:

$ mysql --max-allowed-packet=$((1024*1024*1024)) 

Create a test table with a JSON column and fill it with the longest JSON document you can:

mysql> create table test.jtest ( j json );  mysql> insert into test.jtest    set j = concat('[', repeat('"word",', 100000000), '"word"]'); Query OK, 1 row affected (1 min 49.67 sec)  mysql> select length(j) from test.jtest; +-----------+ | length(j) | +-----------+ | 800000008 | +-----------+ 

This shows that I was able to create a single JSON document with 100 million elements, and MySQL stores this in approximately 800MB.

I didn't try a longer document. I assume it maxes out at 1 GB, which is the largest value you can set for max_allowed_packet.