Netdata Community

Understand MySQL graphs

Greetings
I’ve activated the “MySQL Local” section of NetData and I see the graphs. However I think I don’t understand it. For example, on a very calm mysql (as seen by mytop), NetData show more than 350 requests per second and more than 1000 “read rnd next” handlers…
how can I learn how to read these graphs?
Thanks in advance
Regards

1 Like

Hey!

That’s a very good question indeed. We strive to provide as much information through our dashboard as possible.

A quick question, the MySQL charts do not have descriptions below the chart titles?

Now, let’s take a look at the charts:

According to the MySQL Documentation the `Handler_read_rnd_next is defined as :

The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

So, perhaps an increase in this chart means that your queries are not optimized enough.

According to this StackExchange answer, there is a way to see which queries are not using indexes.

Regarding the requests, some requests originate from Netdata itself, so that it can read the data. We have defined sane default alerts for mysql, so if no alert is activated, you should be good to go :v:

Pinging @vlvkobal and @ilyam8 in case they have more insights

Thanks a lot for taking the time to answer my question.
I’ve read the documentation before posting, but maybe I don’t understand the term “request”. The database receives about 1 SQL request every second, the slow log is empty, so I don’t understand the very high numbers of 350 requests per second and 1000 “read rnd next”…

@Hostmaster_Greg that is a question I would like to find the answer to myself

See the discussion mysql.handlers has 3000 "read rnd next" and 1600 "write" on an *empty* MySQL instance · Issue #10890 · netdata/netdata · GitHub

1 Like