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

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 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 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 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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