> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vortexiq.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Active Async Replicas, MariaDB

> Active Async Replicas for MariaDB instances. Tracked live in Vortex IQ Nerve Centre. How to read it, why it matters, and how to act on it.

**Card class:** [Non-Hero](/nerve-centre/overview#card-classes-explained)  •  **Category:** [Replication](/nerve-centre/connectors#connectors-by-type)

## 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.

|                    |                                                                                                                                                                                                                                         |
| ------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **What it tracks** | Active Async Replicas: the number of replica hosts with a live replication connection to the primary, both I/O and SQL threads running. The detail line is *Active Async Replicas for the selected period.*                             |
| **Data source**    | MariaDB `SHOW REPLICA HOSTS` (formerly `SHOW SLAVE HOSTS`) on the primary, counting registered replicas, cross-checked against `Slave_running` / `Replica_running` status on each replica via `SHOW REPLICA STATUS`.                    |
| **Time window**    | `RT`: real-time, refreshed on each poll.                                                                                                                                                                                                |
| **Alert trigger**  | None on this card. Pair it with [Failover Readiness](/nerve-centre/kpi-cards/mariadb/failover-readiness) and [Async Replication Lag (seconds)](/nerve-centre/kpi-cards/mariadb/async-replication-lag-seconds) for the threshold alerts. |
| **Roles**          | DBA, platform, SRE                                                                                                                                                                                                                      |

## 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.

## 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.

***

### 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](https://app.vortexiq.ai/login) or [book a demo](https://www.vortexiq.ai/contact-us) to see this metric running on your own data.