Users with Large sessions (a_session)

I noticed high growth rate in my mysql binary log. (i.e. 500 MB every 1-2 minute!)
analyzing the binary log, I learned that more than 95% of the binary logs are updates for table sessions
later I realized that I have users which their sessions are considerably huge! even I had a user with 20Mb session (length(a_session)) and every time the user did something new, update for the session, caused a lot of binary log.
I started to delete those sessions so save my server.
but I have 2 questions:
1- what are the data get stored in the sessions? I found this: Need to decode session data or session id information which says map for searches. is there any other?
2- how it could grow up to 20MB? isn’t there any mechanism in the system which can manage size of a_session and remove unnecessary data from a_session?

The binary log is used to recreate the database state.
The session table is to store the users current state.
There is no need to record changes to the session table, since it only records temporary info like login cookies.
You can probably tell the log not to log that table.
As out RT is small, and I don’t use it much, I am not 100% certain of the above, but previous posts look like this is the case:


Jeff, thank you for your comment.
in MySQL to my knowledge, it is not possible to exclude a table from generation binarylog. it is only possible to ignore it on the slave servers to get imported.

for the other references you posted, I had seen them. I started to delete old sessions and big sessions. But still the questions are open

  • what does exactly get stored in the sessions? I read that some of the links to the pages in the searches. I’m looking for more details on the contents
  • what can cause a session to grow as large as 20MB? and how it is possible to limit that?


Perhaps the rt-session-viewer tool will help.

Just run it against a session on one of by instances and it contains
among other things:

Users Preferences
Current users configuration

Best Regards


Hi Martin
I had done it. but I didn’t get the concept. I was able to find the owner of session and bunch of other info. but still struggling to understand how a 20MB+ sessions could get formed!
anyone from BestPractical is highly appreciated if can shed a light on this matter.

I got closer to the root. The largest portion of a_sessions are data stored in "charts_cache"
the users who have this issue, has dashboards which updated frequently and the dashboards include charts
any known/reported bug/behaviour on this issue?