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JSON.DEBUG MEMORY

Syntax​

JSON.DEBUG MEMORY key [path]

Time complexity: O(N) when path is evaluated to a single value, where N is the size of the value, O(N) when path is evaluated to multiple values, where N is the size of the key

ACL categories: @json

Report the memory size in bytes of the JSON element.

Examples

Required arguments​

key

is key to analyze.

Optional arguments​

path

is JSONPath to specify. Default is root $ if not provided.

Return​

Integer reply: memory size in bytes of the JSON value when path is evaluated to a single value.

Array reply: a list that represents the memory size in bytes of JSON value at each path when path is evaluated to multiple values.

Note: Primitive JSON types (numbers, booleans, and null) return 0 because they are stored inline and do not allocate separate memory. Objects, arrays, and strings (that exceed the Small String Optimization buffer) return their actual heap-allocated memory size.

Examples​

Check memory usage of different JSON types

Primitive types (numbers, booleans, null) return 0 bytes as they are stored inline:

dragonfly> JSON.SET primitives $ '{"num":42, "bool":true, "null":null}'
OK

dragonfly> JSON.DEBUG MEMORY primitives $.num
1) (integer) 0

dragonfly> JSON.DEBUG MEMORY primitives $.bool
1) (integer) 0

dragonfly> JSON.DEBUG MEMORY primitives $.null
1) (integer) 0
Check memory usage of objects and arrays

Objects and arrays allocate memory and return their size in bytes:

dragonfly> JSON.SET obj_doc $ '{"a":1, "b":2, "c":{"k1":1,"k2":2}}'
OK

dragonfly> JSON.DEBUG MEMORY obj_doc $.c
1) (integer) 336

dragonfly> JSON.DEBUG MEMORY obj_doc $
1) (integer) 1104

dragonfly> JSON.SET arr_doc $ '[1, 2, 3, 4, 5]'
OK

dragonfly> JSON.DEBUG MEMORY arr_doc $
1) (integer) 80
Check memory usage of strings

Short strings may be optimized (SSO - Small String Optimization) and return 0, while longer strings allocate memory:

dragonfly> JSON.SET short_str $ '{"text":"Hi"}'
OK

dragonfly> JSON.DEBUG MEMORY short_str $.text
1) (integer) 0

dragonfly> JSON.SET long_str $ '{"text":"This is a longer string that should definitely exceed SSO buffer"}'
OK

dragonfly> JSON.DEBUG MEMORY long_str $.text
1) (integer) 112
Check memory usage of multiple paths

When using JSONPath expressions that match multiple values, returns an array of memory sizes:

dragonfly> JSON.SET doc $ '[1, 2.3, "foo", true, null, {}, [], {"a":1, "b":2}, [1,2,3]]'
OK

dragonfly> JSON.DEBUG MEMORY doc $[*]
1) (integer) 0   # 1
2) (integer) 0   # 2.3
3) (integer) 0   # "foo"
4) (integer) 0   # true
5) (integer) 0   # null
6) (integer) 0   # {}
7) (integer) 0   # []
8) (integer) 336  # {"a":1, "b":2}
9) (integer) 48  # [1,2,3]

See also​

JSON.DEBUG FIELDS | JSON.DEBUG HELP