Backing up my Db provokes an error

Howdee all,
I’m using Piwik for a month and needed to create an usual backup of my DB and this morning I had an issue.
This is the error message I had:
Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to allocate 35 bytes) in /myscript/path on line 2650

Oh! Is there a way to fix that and be able to manage my backups as usual?

Thanks in advance for your replies.

Uh oh: forgot to tell the host is provided by 1and1 and memory_limit = 128M in the php.ini file did nothing (except there is no error, but no backup)