MemoryInspector.jl

MemoryInspector.@inspect x

An interactive tool for exploring the sizes of julia objects:

julia> d = Dict(1=>(1,2), 2=>3)
Dict{Int64,Any} with 2 entries:
  2 => 3
  1 => (1, 2)

julia> MemoryInspector.@inspect d
—————————————————————————————————————————————————————————————————————————————————————————————————————————
Select a field to recurse into or ↩ to ascend. [q]uit.

Commands: [J]ump to field path.
Toggles: [v]alue of the current field.

(d)::Dict{Int64,Any} => 480.0 B
   64.0 B internal
3 Allocated Fields:
 → vals::Array{Any,1} => 192.0 B
   keys::Array{Int64,1} => 168.0 B
   slots::Array{UInt8,1} => 56.0 B
   ↩
—————————————————————————————————————————————————————————————————————————————————————————————————————————
Select a field to recurse into or ↩ to ascend. [q]uit.

Commands: [J]ump to field path.
Toggles: [v]alue of the current field.

(d.vals)::Array{Any,1} => 192.0 B
   168.0 B internal
2 Allocated Indexes:
 → 16::Tuple{Int64,Int64} => 16.0 B
   6::Int64 => 8.0 B
   ↩
—————————————————————————————————————————————————————————————————————————————————————————————————————————
Select a field to recurse into or ↩ to ascend. [q]uit.

Commands: [J]ump to field path.
Toggles: [v]alue of the current field.

(d.vals[16])::Tuple{Int64,Int64} => 16.0 B
0 Allocated Indexes:
 → ↩

—————————————————————————————————————————————————————————————————————————————————————————————————————————
Select a field to recurse into or ↩ to ascend. [q]uit.

Commands: [J]ump to field path.
Toggles: [v]alue of the current field.

(1, 2) => 16.0 B
0 Allocated Indexes:
 → ↩

Featuring True Size Accounting!

Importantly (like Base.summarysize(x)) @inspect x is able to account for self-references and shared references inside of objects, so that only the true sizes of fields are displayed! This allows you to correctly investigate the size of truly complex objects.

For example:

julia> mutable struct Obj{T1,T2}
           a::T1
           b::T2
           Obj{A,B}(a::A,b::B) where {A,B} = new{A,B}(a,b)
           Obj{A,B}(a::A) where {A,B} = new{A,B}(a) # Allow partial construction
           Obj{A,B}() where {A,B} = new{A,B}() # Allow partial construction
           Obj(a::A,b::B) where {A,B} = Obj{A,B}(a,b)
       end

julia> s = join(rand('a':'z', 1024*1024)); # 1 MiB string

julia> multistring = Obj(s,s);   # Shared references to large object

julia> selfie = Obj{Obj,Obj}(multistring);

julia> selfie.b = selfie;    # Self-reference

julia> MemoryInspector.@inspect selfie
———————————————————————————————————————————————————
(selfie)::Obj{Obj,Obj} => 1.0 MiB
2 Fields:
   a::Obj{String,String} => 1.0 MiB
 → b::Obj{Obj,Obj} => <self-reference>
   ↩
———————————————————————————————————————————————————
(selfie.b)::Obj{Obj,Obj} => <self-reference>
0 Fields:
 → ↩

———————————————————————————————————————————————————
(selfie)::Obj{Obj,Obj} => 1.0 MiB
2 Fields:
 → a::Obj{String,String} => 1.0 MiB
   b::Obj{Obj,Obj} => <self-reference>
   ↩
———————————————————————————————————————————————————
(selfie.a)::Obj{String,String} => 1.0 MiB
2 Fields:
 → a::String => 1.0 MiB
   b::String => <self-reference>
   ↩
———————————————————————————————————————————————————
(selfie.a.a)::String => 1.0 MiB
0 Fields:
 → ↩

Note that this does mean that sometimes the bytes may be accounted for in a sub-reference that may not match your expectations. This tradeoff between breadth-first and depth-first searching is something we should investigate tuning in the future!

Inspecting Memory via graph and flamegraph layouts:

We support exporting to a PProf profile, via MemoryInspector.@mem_pprof:

julia> d = Dict(1=>2, 2=>"hello", 3=>"hi", ("hi",2)=>3)
Dict{Any,Any} with 4 entries:
  2         => "hello"
  3         => "hi"
  ("hi", 2) => 3
  1         => 2

julia> MemoryInspector.@mem_pprof web=true webport=23222 d
"mem-inspect-profile.pb.gz"

Serving web UI on http://localhost:23222

Graph:

Flamegraph:

Desired Features

See this GitHub Issue for some desired features: #1