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. The more buckets there are, the smaller the deviation is. The deviation range is as follows: [-1.04/2^log2m*1⁄2^,+1.04/2^log2m*1⁄2^]

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 10 to 16

Default value: 14

hll_default_log2explicit

Parameter description: Specifies the default threshold for switching from the explicit mode to the sparse mode.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 0 to 12 The value 0 indicates that the explicit mode is skipped. The value 1 to 12 indicates that the mode is switched when the number of distinct values reaches 2^hll_default_log2explicit^.

Default value: 10

hll_default_log2sparse

Parameter description: Specifies the default threshold for switching from the sparse mode to the full mode.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 0 to 14 The value 0 indicates that the explicit mode is skipped. The value 1 to 14 indicates that the mode is switched when the number of distinct values reaches 2^hll_default_log2sparse^.

Default value: 12

hll_duplicate_check

Parameter description: Specifies whether duplicatecheck is enabled by default.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: 0 or 1 0: disabled; 1: enabled

Default value: 0

hll_default_regwidth (Discarded)

Parameter description: Specifies the number of bits in each bucket for HLL data. A larger value indicates more memory occupied by HLL. hll_default_regwidth and hll_default_log2m determine the maximum number of distinct values that can be calculated by HLL. Currently, regwidth is set to a fixed value and is no longer used.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from 1 to 5

Default value: 5

hll_default_expthresh (Discarded)

Parameter description: Specifies the default threshold for switching from the explicit mode to the sparse mode. Currently, the hll_default_log2explicit parameter is used to replace the similar function.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from -1 to 7 -1 indicates the auto mode; 0 indicates that the explicit mode is skipped; a value from 1 to 7 indicates that the mode is switched when the number of distinct values reaches 2hll_default_expthresh.

Default value: -1

hll_default_sparseon (Discarded)

Parameter description: Specifies whether to enable the sparse mode by default. Currently, the hll_default_log2sparse parameter is used to replace the similar function. When hll_default_log2sparse is set to 0, the sparse mode is disabled.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: 0 or 1 0 indicates that the sparse mode is disabled by default. 1 indicates that the sparse mode is enabled by default.

Default value: 1

hll_max_sparse (Discarded)

Parameter description: Specifies the size of max_sparse. Currently, the hll_default_log2sparse parameter is used to replace the similar function.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: an integer ranging from -1 to 2147483647

Default value: -1

enable_compress_hll (Discarded)

Parameter description: Specifies whether to enable memory optimization for HLL. Currently, the HLL memory has been optimized, and this parameter is no longer used.

This parameter is a USERSET parameter. Set it based on instructions provided in Table 1 GUC parameters.

Value range: Boolean

• on or true indicates that memory optimization is enabled.
• off or false indicates that memory optimization is disabled.

Default value: off