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Add circuit breaker variable #20129

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Add circuit breaker variable #20129

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ee77cde
add circuit breaker variable
rleungx Jan 23, 2025
1682aea
address the comment
rleungx Jun 10, 2025
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10 changes: 10 additions & 0 deletions system-variables.md
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Expand Up @@ -6052,6 +6052,16 @@ For details, see [Identify Slow Queries](/identify-slow-queries.md).
> - `PARALLEL` and `PARALLEL-FAST` modes are incompatible with [`tidb_tso_client_batch_max_wait_time`](#tidb_tso_client_batch_max_wait_time-new-in-v530) and [`tidb_enable_tso_follower_proxy`](#tidb_enable_tso_follower_proxy-new-in-v530). If either [`tidb_tso_client_batch_max_wait_time`](#tidb_tso_client_batch_max_wait_time-new-in-v530) is set to a non-zero value or [`tidb_enable_tso_follower_proxy`](#tidb_enable_tso_follower_proxy-new-in-v530) is enabled, configuring `tidb_tso_client_rpc_mode` does not take effect, and TiDB always works in `DEFAULT` mode.
> - `PARALLEL` and `PARALLEL-FAST` modes are designed to reduce the average time for retrieving TS in TiDB. In situations with significant latency fluctuations, such as long-tail latency or latency spikes, these two modes might not provide any remarkable performance improvements.


### tidb_cb_pd_metadata_error_rate_threshold_pct

- Scope: GLOBAL
- Persists to cluster: Yes
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
- Default value: `0`
- Range: `[0, 1]`
- This variable is used to control when TiDB triggers the circuit breaker. If set to 0 (the default) then the circuit breaker is disabled. If the variable is set to 0.01 to 1 then the circuit breaker is triggered if the error rate percentage, of the specific requests sent to PD, meets or exceeds the threshold.

### tidb_ttl_delete_rate_limit <span class="version-mark">New in v6.5.0</span>

> **Note:**
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