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Metrics type: Supporting Metrics • Category: Replication

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At a glance

The live count of asynchronous replicas currently connected to and replicating from this MariaDB primary. It answers a simple availability question: how many standbys are actively following the primary right now, ready to absorb read traffic or be promoted in a failover? When this number drops below your expected topology, your redundancy has quietly degraded even though the primary itself looks healthy.

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What it tracks

This card surfaces the count of active asynchronous replicas for the selected period, read live from the primary’s view of its replication topology. A replica counts as active only when it holds a live connection to the primary and both replication threads are running: the I/O thread pulling binary-log events and the SQL (apply) thread executing them. A replica that has fallen off the network, stopped with a duplicate-key error, or been taken down for maintenance drops out of the count immediately, which is why this number is your at-a-glance redundancy gauge. Read it against your intended topology: if you run a primary with two read replicas and the card shows one, a standby has gone silent and your failover and read-scaling capacity is halved, even though the primary is serving writes normally. The metric is asynchronous-replica specific; Galera (synchronous, multi-primary) cluster membership is tracked separately by the Galera cards.

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Reconciling against the source

To verify the count directly, run SHOW REPLICA HOSTS; on the primary to list registered replicas, then SHOW REPLICA STATUS\G on each replica and confirm both Slave_IO_Running and Slave_SQL_Running (or the Replica_* equivalents) read Yes. On managed services the active-replica count appears in the provider’s replication view: Amazon RDS / Aurora for MariaDB shows read replicas and their state in the console and via the ReplicaLag / replication-state metrics, while SkySQL and Azure Database for MariaDB surface replica membership in their own consoles. A brief discrepancy between the card and a manual check is usually a timing artefact between poll intervals.

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Tracked live in Vortex IQ Nerve Centre

Active Async Replicas is one of hundreds of KPI pulses Vortex IQ tracks across MariaDB and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English. Start for free or book a demo to see this metric running on your own data.