See www.zabbix.com for the official Zabbix site.
This table contains a surrogate to DBMS sequences for many (but not all) tables and probably was introduced to support the historic "nodes" feature.
|Column||Detail||Default||NULL?||Type||Ref from||Ref to|
|table_name||Name of the affected table.||EMPTY||NOT NULL||varchar(64)|
|field_name||Name of the id field in the affected table.||EMPTY||NOT NULL||varchar(64)|
|nextid||The current maximum id for field_name in table_name - note the discrepancy between the name of this field and what it actually holds.||NONE||NOT NULL||id|
|PRIMARY KEY||YES||table_name, field_name|