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docs: Document default change for legacy-replication-lag-algorithm flag #2030

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2 changes: 1 addition & 1 deletion content/en/docs/24.0/reference/programs/vtgate/_index.md
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Expand Up @@ -126,7 +126,7 @@ vtgate \
--keep-logs-by-mtime duration keep logs for this long (using mtime) (zero to keep forever)
--keyspaces-to-watch strings Specifies which keyspaces this vtgate should have access to while routing queries or accessing the vschema.
--lameduck-period duration keep running at least this long after SIGTERM before stopping (default 50ms)
--legacy-replication-lag-algorithm Use the legacy algorithm when selecting vttablets for serving. (default true)
--legacy-replication-lag-algorithm (DEPRECATED) Use the legacy algorithm when selecting vttablets for serving.
--lock-heartbeat-time duration If there is lock function used. This will keep the lock connection active by using this heartbeat (default 5s)
--lock-timeout duration Maximum time to wait when attempting to acquire a lock from the topo server (default 45s)
--log-err-stacks log stack traces for errors
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8 changes: 8 additions & 0 deletions content/en/docs/24.0/user-guides/configuration-advanced/query-load-balancing.md
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Expand Up @@ -5,6 +5,14 @@ weight: 12

For applications which scale out read queries using replicas, Vitess can safely avoid sending queries to replicas with replication lag beyond acceptable thresholds.

{{< info >}}
**Note:** Starting in Vitess v24, VTGate uses a simpler default algorithm for handling replication lag based on low lag thresholds, high lag thresholds, and minimum number of tablets. This algorithm is more stable in production environments.

The legacy algorithm is deprecated and will be removed in a future release.

For more details about the algorithm change, see the [v24.0 release notes](https://github.com/vitessio/vitess/blob/main/changelog/24.0/24.0.0/summary.md#vtgate-new-default-legacy-replication-lag-algorithm).
{{< /info >}}

## Flags

You can set the following flags on VTGate to control load-balancing of read queries for replicas:
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