Redis blocked by slow query, cannot use SLOWLOG

[Lukas Rieder]

Hi,

first of all sorry if this post shows up twice. I used the Google Web interface and my post didn’t show up, so I decided to write one with my E-Mail client.

Today I was working on a live issue that involved an unresponsive Redis instance.

I went on the server and connected with Redis in order to investigate what query is blocking the process.

But using SLOWLOG Redis I only got "BUSY Redis is busy running a script. You can only call SCRIPT KILL or SHUTDOWN NOSAVE”

So the database was continued to be hit with those slow queries, since this was all live.

Eventually I could get a hold of the content of the slowlog by executing SCRIPT KILL and SLOWLOG GET 1 in quick succession.

I am posting this here, because I think it would be helpful to have SLOWLOG logged to somewhere else. I searched around for such a solution but I couldn’t find anything.

Cheers,

Lukas Rieder | Backend Developer

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[alex]

For this reasons when a script executes for more than the specified time the following happens:

• Redis logs that a script is running too long.
• It starts accepting commands again from other clients, but will reply with a BUSY error to all the clients sending normal commands. The only allowed commands in this status are SCRIPT KILL and SHUTDOWN NOSAVE.
• It is possible to terminate a script that executes only read-only commands using the SCRIPT KILL command. This does not violate the scripting semantic as no data was yet written to the dataset by the script.
• If the script already called write commands the only allowed command becomes SHUTDOWN NOSAVE that stops the server without saving the current data set on disk (basically the server is aborted).