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Add some docs on VTGate buffering for MoveTables and Reshard traffic …
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Signed-off-by: Matt Lord <mattalord@gmail.com>
mattlord committed Apr 25, 2024
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2 changes: 1 addition & 1 deletion content/en/docs/20.0/concepts/move-tables.md
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title: MoveTables
---

MoveTables is a new workflow based on VReplication. It enables you to relocate tables between keyspaces, and therefore physical MySQL instances, without downtime.
MoveTables is a workflow based on VReplication. It enables you to relocate tables between keyspaces, and therefore physical MySQL instances, without downtime.

## Identifying Candidate Tables

13 changes: 13 additions & 0 deletions content/en/docs/20.0/reference/features/vtgate-buffering.md
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outages/fail overs, etc.)
{{< /warning >}}

## What happens during a MoveTables or Reshard SwitchTraffic or ReverseTraffic with Buffering

Fundamentally Vitess will:

* Hold up and buffer any queries sent to the tables (MoveTables) or shards (Reshard) for which traffic is being switched.
* Perform the traffic switching work so that application traffic against the tables (MoveTables) or shards (Reshard) are transparently switched to the new keyspace (MoveTables) or shards (Reshard).
* Drain the buffered queries to the new keyspace or shards — or if the switch failed then back to the original keyspace or shards.

{{< warning >}}
This process is not guaranteed to eliminate errors to the application, but
rather reduce them or make them less frequent. The application should still
endeavor to handle errors appropriately if/when they occur.
{{< /warning >}}

## How does it work?

8 changes: 8 additions & 0 deletions content/en/docs/20.0/reference/vreplication/movetables.md
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[`switchtraffic`](../../programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_switchtraffic/) switches traffic forward for the `tablet-types` specified. You can switch all traffic with just one command, and this is the default behavior. Note that you can now switch replica, rdonly, and primary traffic in any order.

{{< info >}}
Note that VTGate can [buffer queries](../../features/vtgate-buffering/) when switching traffic which can virtually eliminate any visible impact on application users.
{{</ info >}}

</div>

#### ReverseTraffic
<div class="cmd">

[`reversetraffic`](../../programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_reversetraffic/) switches traffic in the reverse direction for the `tablet-types` specified. The traffic should have been previously switched forward using `SwitchTraffic` for the `cells` and `tablet-types` specified.

{{< info >}}
Note that VTGate can [buffer queries](../../features/vtgate-buffering/) when switching traffic which can virtually eliminate any visible impact on application users.
{{</ info >}}

</div>

#### Cancel
8 changes: 8 additions & 0 deletions content/en/docs/20.0/reference/vreplication/reshard.md
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[`SwitchTraffic`](../../programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_switchtraffic) switches traffic forward for the `tablet-types` specified. This replaces the previous `SwitchReads` and `SwitchWrites` commands with a single one. It is now possible to switch all traffic with just one command, and this is the default behavior. Also, you can now switch replica, rdonly and primary traffic in any order: earlier you needed to first `SwitchReads` (for replicas and rdonly tablets) first before `SwitchWrites`.

{{< info >}}
Note that VTGate can [buffer queries](../../features/vtgate-buffering/) when switching traffic which can virtually eliminate any visible impact on application users.
{{</ info >}}

</div>

#### ReverseTraffic
<div class="cmd">

[`ReverseTraffic`](../../programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_reversetraffic/) switches traffic in the reverse direction for the `tablet-types` specified. The traffic should have been previously switched forward using `SwitchTraffic` for the `cells` and `tablet_types` specified.

{{< info >}}
Note that VTGate can [buffer queries](../../features/vtgate-buffering/) when switching traffic which can virtually eliminate any visible impact on application users.
{{</ info >}}

</div>

#### Cancel

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