Trends and history storage time
Let's cover another important point that is, at times, forgotten by Zabbix administrators. Differently from other monitoring tools, Zabbix allows each item to have its own time for data holding configured individually. There are two ways for this to occur.
History tables
Zabbix works with five history tables, two of which are used to store numerical data (history and history_unit).
Each item can have its own retention time defined in the History storage period field (in days). This period defines the maximum amount of time (in days) that the collected values from the particular item will remain in the database.
After this period, an internal process called housekeeping will remove the old data from the database. This function creates concurrency competition for reading and writing. At this point, the housekeeping tool needs to select the data that will be erased and also issue DELETE SQL statements that will be generated to eliminate this data.
