HyperLogLog

hll_default_log2m

Parameter description: Specifies the number of buckets for HLL data. The number of buckets affects the precision of distinct values calculated by HLL. More buckets indicate a smaller deviation. The deviation range is as follows: [–1.04/2^log2m*1/2, +1.04/2^log2m*1/2] This parameter can be set at the PDB level.

Parameter type: integer

Unit: none

Value range: 10 to 16

Default value: 14. In the PDB scenario, if this parameter is not set, the global setting is inherited.

Setting method: This is a USERSET parameter. Set it based on instructions provided in Table 1.

Setting suggestion: Retain the default value or adjust the value based on service requirements.

Risks and impacts of improper settings: If the value is too small, the required precision cannot be met. If the value is too large, resources may be wasted.

hll_default_log2explicit

Parameter description: Specifies the default threshold for switching from the explicit mode to the sparse mode. This parameter can be set at the PDB level.

Parameter type: integer

Unit: none

Value range: 0 to 12

• 0: The explicit mode is skipped.
• 1 to 12: The mode is switched when the base value reaches 2^{hll_default_log2explicit}.

Default value: 10. In the PDB scenario, if this parameter is not set, the global setting is inherited.

Setting method: This is a USERSET parameter. Set it based on instructions provided in Table 1.

Setting suggestion: Retain the default value or adjust the value based on service requirements.

Risks and impacts of improper settings: If the value is too small, the required precision cannot be met. If the value is too large, resources may be wasted.

hll_default_log2sparse

Parameter description: Specifies the default threshold for switching from the sparse mode to the full mode. This parameter can be set at the PDB level.

Parameter type: integer

Unit: none

Value range: 0 to 14

• 0: The explicit mode is skipped.
• 1 to 14: The mode is switched when the base value reaches 2^{hll_default_log2sparse}.

Default value: 12. In the PDB scenario, if this parameter is not set, the global setting is inherited.

Setting method: This is a USERSET parameter. Set it based on instructions provided in Table 1.

Setting suggestion: Retain the default value or adjust the value based on service requirements.

Risks and impacts of improper settings: If the value is too small, the required precision cannot be met. If the value is too large, resources may be wasted.

hll_duplicate_check

Parameter description: Specifies whether duplicatecheck is enabled by default.

Parameter type: integer

Unit: none

Value range: 0 to 1

• 0: The function is disabled by default.
• 1: The function is enabled by default.

Default value: 0

Setting method: This is a USERSET parameter. Set it based on instructions provided in Table 1.

Setting suggestion: Retain the default value or adjust the value based on service requirements.

Risks and impacts of improper settings: If this parameter is enabled, more resources may be consumed for duplicate check, but the accuracy of distinct value calculation is improved.