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Add circuit breaker variable #20129

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Add circuit breaker variable #20129

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aca1baf
add circuit breaker variable
rleungx Jan 23, 2025
58b886c
address the comment
rleungx Jun 10, 2025
b66f65d
address the comment
rleungx Jun 24, 2025
03f5e6e
Apply suggestions from code review
hfxsd Jun 30, 2025
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9 changes: 9 additions & 0 deletions system-variables.md
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Expand Up @@ -6052,6 +6052,15 @@ 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_ratio <span class="version-mark">New in v9.0.0</span>

- 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 controls when TiDB triggers the circuit breaker. A value of `0` (default) disables the circuit breaker. A value between `0.01` and `1` enables it, causing the circuit breaker to trigger when the error rate of specific requests 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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