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Update throttler config docs for v17 #1489

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Jun 6, 2023
Merged

Update throttler config docs for v17 #1489

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1f8994a
Update throttler config docs for v17
shlomi-noach Jun 5, 2023
61bfb9f
fixed per reivew
shlomi-noach Jun 5, 2023
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30 changes: 20 additions & 10 deletions content/en/docs/17.0/reference/features/tablet-throttler.md
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Expand Up @@ -109,11 +109,20 @@ Configuration in v16 differs from v15 and earlier. Please note the different con

`v16` is backwards compliant with `v15` and still default to the `v15` configuration. We illustrate both configurations so that you understand how to transition from one to the other.

### v16 and forward
### v17 and forward

In `v16`, throttler configuration is found in the [local topology server](../../../concepts/topology-service/). There is one configuration per keyspace. All shards and all tablets in all cells have the same throttler configuration: they are all enabled or disabled, and all share the same threshold or custom query. Since configuration is stored outside the tablet, it survives tablet restarts.
In `v17`, throttler configuration is found in the [local topology server](../../../concepts/topology-service/). There is one configuration per keyspace. All shards and all tablets in all cells have the same throttler configuration: they are all enabled or disabled, and all share the same threshold or custom query. Since configuration is stored outside the tablet, it survives tablet restarts.

`v16` introduced a new opt-in `vttablet` flag, `--throttler-config-via-topo`. In `v16` this flag defaulted `false`. In `v17` this flag now defaults `true`. With `--throttler-config-via-topo` set, the tablet will look for configuration in the topology server, and will watch and apply any changes made there.

When the flag `--throttler-config-via-topo` is set (and it is set by default), the following flags are ignored even if specified. These flags are scheduled to be removed in `v18`and `v19`:

- `--enable_lag_throttler`
- `--throttle_threshold`
- `--throttle_metrics_query`
- `--throttle_metrics_threshold`
- `--throttle_check_as_check_self`

`v16` is backward compliant with `v15` and therefore to use the new configuration you must opt-in with the `vttablet` flag `--throttler-config-via-topo` (boolean, disabled by default). With `--throttler-config-via-topo` set, the tablet will look for configuration in the topology server, and will watch and apply any changes made there.

Updating the throttler config is done via `vtctlclient` or `vtctldclient`. For example:

Expand All @@ -124,13 +133,14 @@ $ vtctldclient UpdateThrottlerConfig --disable commerce

See [vtctl UpdateThrottlerConfig](../../programs/vtctl/throttler#updatethrottlerconfig).

To transition from a `v15` configuration to `v16`, first populate topo with a new throttler configuration. At the very least, set a `--threshold`. You likely also want to `--enable`. Then, reconfigure `vttablet`s with `--throttler-config-via-topo`, and restart them.
If you are still using the `v15` flags, we recommend that you transition to the new throttler configuration scheme: first populate topo with a new throttler configuration via `UpdateThrottlerConfig`. At the very least, set a `--threshold`. You likely also want to `--enable`. Then, reconfigure `vttablet`s with `--throttler-config-via-topo`, and restart them.


### v15 and before
### v16 and before

In `v15` and earlier versions, the throttler is configured per tablet. Each tablet can have throttler enabled/disabled independently, or have different thresholds.
In earlier versions, the throttler is configured per tablet. Each tablet can have throttler enabled/disabled independently, or have different thresholds.

`v16` supports the `v15` configuration, but this support may be removed in `v17`.
`v17` still supports the per-tablet configuration if you specify `--throttler-config-via-topo=false`, but this will be removed in `v18`.

- The throttler is **disabled** by default. Use the `vttablet` option `--enable-lag-throttler` to enable the throttler.
When the throttler is disabled, it still serves `/throttler/check` and `/throttler/check-self` API endpoints, and responds with `HTTP 200 OK` to all requests.
Expand All @@ -148,9 +158,9 @@ An example for custom query & threshold setup, using the MySQL metrics `Threads_

```shell
$ vttablet
-throttle_metrics_query "show global status like 'threads_running'"
-throttle_metrics_threshold 150
-throttle_check_as_check_self
--throttle_metrics_query "show global status like 'threads_running'"
--throttle_metrics_threshold 150
--throttle_check_as_check_self
```

## Heartbeat configuration
Expand Down