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Add circuit breaker variable (#20129) #22171

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3994624
add circuit breaker variable
rleungx Jan 23, 2025
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address the comment
rleungx Jun 10, 2025
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address the comment
rleungx Jun 24, 2025
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hfxsd Jun 30, 2025
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hfxsd Oct 9, 2025
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Update system-variables.md
hfxsd Dec 12, 2025
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9 changes: 9 additions & 0 deletions system-variables.md
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Expand Up @@ -6304,6 +6304,15 @@ 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 v8.5.5</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. Setting a value of `0` (default) disables the circuit breaker. Setting a value between `0.01` and `1` enables it, causing the circuit breaker to trigger when the error rate of specific requests sent to PD reaches or exceeds the threshold.

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

> **Note:**
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