| Items are delayed and the queue keeps growing | Which items are delayed and which poller type serves them, then process utilization against the 75 percent line in the Zabbix server health template. A few unreachable devices can hold pollers busy and delay everything behind them. | Poller counts and timeouts, unreachable-host handling, or a proxy closer to the devices |
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| History cache fills and values are written late | History cache usage against the template's 75 percent alert, then history syncer utilization and write latency on the database. A full history cache means the database cannot absorb writes as fast as the pollers produce them. | Database I/O and indexes, then HistoryCacheSize and syncer count |
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| The value cache is in low-memory mode | Value cache usage against its 95 percent alert and the items that read history: triggers with long time windows, calculated items and dashboards. The template raises a High severity alert when low-memory mode is on. | ValueCacheSize against what triggers actually read, or shorter trigger windows |
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| The database is busy and the housekeeper never finishes | Housekeeper utilization, retention for history and trends against table size, and whether per-item storage periods or the global override apply. With TimescaleDB, the housekeeper will not drop outdated partitions unless the override options are on. | Retention and override settings, partitioning, or TimescaleDB compression where the license allows it |
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| The server will not start, or the schema upgrade is still running after an upgrade | The server log for the database version it found, and whether the schema upgrade is still running. Zabbix warns that the upgrade may take a long time depending on database size. On MySQL and MariaDB with binary logging, a 6.0 upgrade needs superuser privileges or log_bin_trust_function_creators = 1. | Let the upgrade finish, fix the privilege or database version floor, or restore from backup on a planned window |
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| A proxy stopped sending data after the server was upgraded | The proxy version against the server's. Zabbix supports proxies of the same major version fully and proxies no older than the previous LTS with limited functionality; anything older or newer is ignored with a warning. SQLite proxies also lose stored history if their database file is older than the new version requires. | Upgrade the proxy to a supported version, and plan SQLite proxy history loss in advance |
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| After a failover the frontend shows the wrong node or HA nodes flap | HANodeName and NodeAddress on each node, the failover delay (one minute by default, 10 seconds to 15 minutes allowed) and database replication health. Standby nodes watch the active node's heartbeat and take over when it goes stale. | Node names and addresses, failover delay, or the replication problem behind the flapping |
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| Alerts storm, duplicate or arrive without context | The problem and event history for the trigger, trigger dependencies, action conditions and the media type log. A single failed switch pages for every host behind it when no dependency is set. | Trigger dependencies, action conditions and escalation, then maintenance periods |
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