writing_throttling_trigger_percentage

Description

writing_throttling_trigger_percentage specifies the threshold for write speed.

Privilege requirements

• Query the parameter

  sys tenant and all user tenants can use the SHOW PARAMETERS statement or the GV$OB_PARAMETERS view to query this parameter.

• Modify the parameter

  sys tenant and user tenants can modify this parameter.

Attributes

Considerations

• OceanBase Database stores recently written data in MemStore. To prevent memory overflow, the system provides two important protection mechanisms:

  • Freezing mechanism: Data in memory is persisted to disk to release memory space.

  • Throttling mechanism: When memory pressure is high, the write speed is reduced to gain time for memory release.

  These two mechanisms are controlled by two tenant-level parameters: freeze_trigger_percentage (freezing threshold) and writing_throttling_trigger_percentage (throttling threshold).

  To avoid performance degradation caused by premature throttling, the value of writing_throttling_trigger_percentage must be greater than that of freeze_trigger_percentage.

• For V4.0.0, the default value of this parameter is changed to 60. This is because the throttling feature is very stable and is rarely triggered except for sudden import traffic in most business scenarios. In import scenarios, throttling is better than stopping writes. To achieve smooth throttling, the trigger point is set to 60 instead of 80. If the trigger point is set to 80, the remaining 20% buffer will be consumed to relieve the 80% MEMStore memory usage, resulting in a very abrupt throttling effect and a significant increase in response time on the business side.

• When the memory used by MemStore reaches this threshold, write throttling is triggered. If the value of this parameter is 100, write throttling is disabled.

Examples

Set the write speed threshold to 60.

obclient> ALTER SYSTEM SET writing_throttling_trigger_percentage = 60;

References

Tenant memory full