The Case

Securing MySQL is always a challenge. There are general best practices that can be followed for securing your installation, but the more complex setup you have the more likely you are to face some issues which can be difficult to troubleshoot.

We’ve recently been working on a case (thanks Alok Pathak and Janos Ruszo for their major contribution to this case) where MySQL started becoming unavailable when threads activity was high, going beyond a threshold, but not always the same one.

During that time there were many logs like the following, and mysqld was becoming unresponsive for a few seconds.

2019-11-27T10:26:03.476282Z 7736563 [Note] Got an error writing communication packets
2019-11-27T10:26:03.476305Z 7736564 [Note] Got an error writing …

Very often MySQL is much less stable than we realize. In this video I explain how to detect and dianose these MySQL stalls that last for 5-10 seconds or more.

The reason nobody knows about these issues is that they’re:
a) rare
b) intermittent
c) monitoring software can’t catch them

You can use pt-stalk to detect and diagnose such issues. All of the tools I have mentioned in this video are part of Percona Toolkit (no wonder they all start with PT), you can find the toolkit here:

Percona Toolkit

Here’s the main commands I have discussed in this video:

Starting pt-stalk in foreground

# pt-stalk

Starting pt-stalk in background with email notification:

# pt-stalk …