MySQL flexible schema and JSON for Internet of Things

● Part 1: IoT demo
● Part 2: MySQL, JSON and Flexible storage

…
$ node particle_mysql_all.js
Starting...
INSERT INTO cloud_data_json (name, data) values ('particle',
'{"data":"null","ttl":60,"published_at":"2017-09-28T19:40:49.869Z","coreid":"1f0039000947343337373738
","name":"Server Error"}')
...

console.log("Starting...");
var Particle = require('particle-api-js');
var particle = new Particle();
fs = require('fs')
var token = fs.readFileSync('.token', 'ascii').replace(/n$/, '');
//Get your devices events
// MySQL Connection
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'photon',
password : 'photon',
database : 'particle'
});

...
particle.getEventStream({deviceId: 'mine', auth: token}).then(function(stream) {
stream.on('event', function(data) {
var query = connection.query(' INSERT INTO cloud_data (name, data) values
(?, ?)', [data.name, data.data], function(err, result) {
if (err) {
console.log('Error in ' + query.sql + err);
}
});
console.log(query.sql);
});
});

Storing data in MySQL …
$ mysql
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 19
Server version: 8.0.3-rc MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql>

CREATE TABLE `sensor_wide` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`light` int(11) DEFAULT NULL,
`temp` double DEFAULT NULL,
`humidity` double DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB
alter table sensor_wide
add water_level double ...;

CREATE TABLE `cloud_data` (
`name` varchar(255) DEFAULT NULL,
`data` text DEFAULT NULL,
`updated_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
PRIMARY KEY (`id`)
) ENGINE=InnoDB
+ More Flexible
- High overhead on storage

Everyone knows what JSON is, right?

CREATE TABLE `cloud_data_json` (
`name` varchar(255) DEFAULT NULL,
`data` JSON,
`updated_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
PRIMARY KEY (`id`)
) ENGINE=InnoDB;
+ Most Flexible + Indexes
- Overhead on storage

...
stream.on('event', function(data) {
var query = connection.query(
'INSERT INTO cloud_data_json (client_name, data)
VALUES (?, ?)',
['particle', JSON.stringify(data)]
)
...
(demo)

select data->>'$.name' as data_name,
data->>'$.data' as data,
data->>'$.published_at' as published
from cloud_data_json
order by data->'$.published_at' desc
limit 10;

EXPLAIN select data->>'$.name' as data_name …
order by data->>'$.published_at' desc limit 10
select_type: SIMPLE
table: cloud_data_json
partitions: NULL
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 101589
filtered: 100.00
Extra: Using filesort

mysql> ALTER TABLE cloud_data_json
-> ADD published_at DATETIME(6)
-> GENERATED ALWAYS AS
(STR_TO_DATE(data->>'$.published_at',"%Y-%m-%dT%T.%fZ")) VIRTUAL;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE cloud_data_json
-> ADD data_name VARCHAR(255)
-> GENERATED ALWAYS AS (data->>'$.name') VIRTUAL;

mysql> alter table cloud_data_json add key (published_at);
mysql> explain select data_name, published_at, data->>'$.data' as data from
cloud_data_json order by published_at desc limit 10G
partitions: NULL
type: index
possible_keys: NULL
key: published_at
key_len: 9
ref: NULL
rows: 10
filtered: 100.00
Extra: Backward index scan

cloud_data_json order by published_at desc, data_name asc limit 10G
select_type: SIMPLE
partitions: NULL
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 101589
filtered: 100.00
Extra: Using filesort

mysql> alter table cloud_data_json
add key published_at_data_name
(published_at desc, data_name asc);
New in MySQL 8.0

cloud_data_json order by published_at desc limit 10G
select_type: SIMPLE
partitions: NULL
type: index
possible_keys: NULL
key: published_at_data_name
key_len: 267
ref: NULL
rows: 10
filtered: 100.00
Extra: NULL

JSON field type was introduced in 5.7, improved in 8.0
● Partial updates
○ in-place update of a JSON column instead of removing the old
document and writing the new document in its entirety to the
column
○ Only functions are supported: JSON_SET(), JSON_REPLACE(),
or JSON_REMOVE()
Use JSON_STORAGE_FREE(json_val) to see how much storage space was
freed in its binary representation after it was updated in place

mysql> select json_pretty(data) from cloud_data_json
where data->>'$.data' like '%beer%' limit 1G
...
json_pretty(data): {
"ttl": 60,
"data": "FvGav,tagkey=beer-store spFridge=7.00,pvFridge=7.44",
"name": "LOG_DATA_DEBUG",
"coreid": "3600....",
"published_at": "2017-09-28T18:21:16.517Z"
}

mysql> alter table cloud_data_json_indexes add fulltext key (data);
ERROR 3152 (42000): JSON column 'data' supports indexing only via generated columns on
a specified JSON path.
mysql> ALTER TABLE cloud_data_json_indexes
-> ADD data_data VARCHAR(255)
-> GENERATED ALWAYS AS (data->>'$.data') VIRTUAL;
mysql> alter table cloud_data_json_indexes add fulltext key ft_json(data_name,
data_data);
ERROR 3106 (HY000): 'Fulltext index on virtual generated column' is not supported for
generated columns.

-> ADD data_name VARCHAR(255) CHARACTER SET UTF8MB4
-> GENERATED ALWAYS AS (data->>'$.name') STORED;
mysql> alter table cloud_data_json_indexes add fulltext key ft_json(data_name);
Query OK, 0 rows affected, 1 warning (3.78 sec)
mysql> show warnings;
+---------+------+--------------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------------+
| Warning | 124 | InnoDB rebuilding table to add column FTS_DOC_ID |
+---------+------+--------------------------------------------------+

-> ADD data_data TEXT CHARACTER SET UTF8MB4
-> GENERATED ALWAYS AS ( CONVERT(data->>'$.data' USING UTF8MB4) ) STORED;
mysql> alter table cloud_data_json_indexes drop key ft_json,
add fulltext key ft_json(data_name, data_data);

● JSON aggregation functions
○ JSON_ARRAYAGG()
○ JSON_OBJECTAGG()
mysql> SELECT JSON_ARRAYAGG(`key`) AS `keys` FROM t1;
+--------------------------+
| keys |
+--------------------------+
| [ "key1",
"key2",
"key3" ]
|
+--------------------------+
1 row in set (0,00 sec)

Other uses for JSON and flexible storage
● Custom fields (CMS)
● Complex structures
● Etc

MySQL flexible schema and JSON for Internet of Things

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