TOPK.RESERVE

TOPK.RESERVE creates an empty Top-K structure at key. It keeps the topk items seen most often, with estimated counts, in a fixed amount of memory, so you can find heavy hitters (popular products, noisy clients, trending terms) without storing a counter per item.

The Top-K must exist before you add to it.

Arguments

Argument	Effect
topk	How many items to keep, 1 to 4294967295.
width	Counters per row used to estimate counts (default 8). More counters give more accurate counts and take more memory.
depth	Number of counter rows (default 7). More rows make large errors less likely and take more memory.
decay	A value above 0 and at most 1 (default 0.9) that sets how readily rare items give way to frequent ones.

width, depth and decay are given together or not at all.

Return value

Case	RESP2	RESP3
Created	Simple string OK	Simple string OK

Error replies:

• TopK: key already exists if the key exists (with any type).
• TopK: invalid k, TopK: invalid width, TopK: invalid depth
• TopK: invalid decay value. must be '<= 1' & '> 0'
• TopK: Insufficient memory to create the key
• ERR wrong number of arguments for 'topk.reserve' command when only some of width, depth, decay are given.

Examples

127.0.0.1:6379> TOPK.RESERVE trending 3
OK
127.0.0.1:6379> TOPK.INFO trending
1) k
2) (integer) 3
3) width
4) (integer) 8
5) depth
6) (integer) 7
7) decay
8) "0.9"
127.0.0.1:6379> TOPK.RESERVE trending 5
(error) TopK: key already exists
127.0.0.1:6379> TOPK.RESERVE wide 10 100 5 0.9
OK

Compatibility

Same arguments and defaults as TOPK.RESERVE in RedisBloom.

See also

TOPK.ADD, TOPK.INCRBY, TOPK.LIST, TOPK.INFO