[Haskell-cafe] Debugging ByteString and Data.Binary.Get memory usage

Johan Tibell johan.tibell at gmail.com
Fri Aug 30 00:47:23 CEST 2013

A good starting point is to estimate how much space you think the data
should take using e.g.


If you do that, is the actual space usage close to what you expected?

On Thu, Aug 29, 2013 at 5:35 PM, Kyle Hanson <hanooter at gmail.com> wrote:

> OK
> I have a bunch of BSON documents that I convert to ByteStrings, put in a
> Map, and write to a socket based on the response. I noticed some high
> memory usage (in the GBs) so I decided to investigate. I simplified my
> problem into a small program that demonstrates clearer what is happening.
> I wrote two versions, one with a Lazy Map and Lazy ByteStrings and one
> with a Strict Map and Strict ByteStrings. Both share the same memory
> behavior (except the lazy BS one is faster)
> Here is the strict version:
> http://lpaste.net/92298
> And here is the lazy version:
> http://lpaste.net/92299
> I wrote this and compared the memory and speed behavior of ByteStrings
> generated by converting it from a BSON document and ByteStrings generated
> more purely.
> The length of the ByteString from a BSON document is 68k and the length of
> the "pure" BS is 70k.
> This is my weird memory behavior, both BSON and "pure" methods use the
> same amount of memory after inserting 10k of them (90mb)
> However when I go to lookup a value, the BSON Map explodes the memory to
> over 250mb. Even if I lookup just 1 value. Looking up any number of values
> in the "pure BS" keeps the memory usage stable (90mb).
> I am hoping someone can help me understand this. I have read some posts
> about Temporary ByteStrings causing memory issues but I don't know how to
> get started debugging.
> --
> Kyle Hanson
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