It usually means your MySQL server has run out of heap space.

Alert entries (and entries for port stats and some other things) are held in MySQL memory tables, which need heap space.

You can change the heap size in your my.cnf : 

[mysqld]
tmp_table_size=2G
max_heap_table_size=2G
2GB might be OTT, depends how big your deployment is :)

adam.

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