[Haskell-cafe] Debugging ByteString and Data.Binary.Get memory usage
bob at redivi.com
Fri Aug 30 06:43:18 CEST 2013
foldl' is the right way to simulate the sequential IO action, foldr would
be doing it in reverse (and for large enough input will stack overflow).
On Thu, Aug 29, 2013 at 9:33 PM, Kyle Hanson <hanooter at gmail.com> wrote:
> Thanks Bob,
> I made it foldr because it was meant to simulate the sequential IO action
> that my server uses to populate the Map.
> I found the problem to be that I need to force the map to evaluate so
> adding a little $! fixed the problem
> Kyle Hanson
> On Thu, Aug 29, 2013 at 9:09 PM, Bob Ippolito <bob at redivi.com> wrote:
>> Building a map with foldr seems unwise, have you tried doing it with
>> fromListWith instead? Or foldl'? In either case, since you don't even put
>> the map into WHNF, none of the computation is done at all in either case
>> until the first lookup.
>> On Thu, Aug 29, 2013 at 3:35 PM, Kyle Hanson <hanooter at gmail.com> wrote:
>>> 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:
>>> And here is the lazy version:
>>> 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
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe at haskell.org
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