Steps to reproduce:

1. Upgrade Zabbix to 5.0.2 version with PostgreSQL 11 and TimescaleDB extension with big history* tables
2. Check latest data

Result:

1. Getting heavy query and slow web response

Rootcause is SQL query

SELECT itemid FROM history WHERE itemid IN (itemid1,itemid2,itemid3,...) GROUP BY itemid HAVING MAX(clock)>$period

Query generated by getItemsHavingValuesFromSql function from CHistoryManager.php

Suggested alternative:

with cleaned as(select itemid from history where clock >$period) select distinct itemid from cleaned where itemid in((itemid1,itemid2,itemid3,...);

Rollback to 5.0.1 Frontend version have fixed the issue

Execution plan for

current SQL

and

Suggested SQL