Hash

Hash

The cbstats hash command provides information on vBucket hash tables.

Description

Requesting these stats does affect performance, so don’t do it too regularly, but it’s useful for debugging certain types of performance issues. For example, if your hash table is tuned to have too few buckets for the data load within it, the max_depth will be too large and performance will suffers.

It is also possible to get more detailed hash tables stats by using ‘hash detail’. This prints per-vbucket stats. Each stat is prefixed with vb_ followed by a number, a colon, then the individual stat name. For example, the stat representing the size of the hash table for vbucket 0 is vb_0:size=.

Syntax

Request syntax:

cbstats [hostname]:11210 hash
cbstats [hostname]:11210 hash detail
		

Example: hash

Request example:

cbstats 10.5.2.54:11210 hash

Example: hash detail

Request example:

cbstats 10.5.2.54:11210 hash detail

Response: hash

Example response:


 avg_count:    0
 avg_max:      0
 avg_min:      0
 largest_max:  0
 largest_min:  0
 max_count:    0
 min_count:    0
 total_counts: 0
			
Stat Description
avg_count The average number of items per vbucket
avg_max The average max depth of a vbucket hash table
avg_min The average min depth of a vbucket hash table
largest_max The largest hash table depth of in all vbuckets
largest_min The largest minimum hash table depth of all vbuckets
max_count The largest number of items in a vbucket
min_count The smallest number of items in a vbucket
total_counts The total number of items in all vbuckets

Response: hash detail

Example response:


 avg_count:                0
 avg_max:                  0
 avg_min:                  0
 largest_max:              0
 largest_min:              0
 max_count:                0
 min_count:                0
 total_counts:             0
 vb_0:counted:             0
 vb_0:locks:               5
 vb_0:max_depth:           0
 vb_0:mem_size:            0
 vb_0:mem_size_counted:    0
 vb_0:min_depth:           0
 vb_0:reported:            0
 vb_0:resized:             0
 vb_0:size:                3079
 vb_0:state:               replica
 ...
			
Stat Description
state The current state of this vbucket
size Number of hash buckets
locks Number of locks covering hash table operations
min_depth Minimum number of items found in a bucket
max_depth Maximum number of items found in a bucket
reported Number of items this hash table reports having
counted Number of items found while walking the table
resized Number of times the hash table resized
mem_size Running sum of memory used by each item
mem_size_counted Counted sum of current memory used by each item