Memory usage of (port->lines ...) is extreamly high

[Hong Yang]

Hi Racketer

I'm trying to load a log file which size is 600MB, then I found the program exhausted 3 GB resident memory just for load all the content of it via (port->lines...). I do have enough RAM but it looks like some thing went wrong here, and I do need to load them all into RAM for my use case so (read-line ...) doesn't help me.

Any comment would be preciated.

Here is may programe:

#!/usr/bin/racket
#lang racket

; Load input as list of lines
(define (input-load-lines file-name)
  (if (file-exists? file-name)
      (let* ([input (open-input-file file-name)]
             [lines (port->lines input)])
        (close-input-port input)
        lines)
      empty))

; Racket 7.8, compile from source code, (none cs mode)
; 100M of log requires 0.5G runtime memory
; 300M of log requires 1.5G runtime memory
; 600M of log requires 3.0G runtime memory
;
; Reference
;   racket/collects/racket/port.rkt :106
;   racket/collects/racket/private/portlines.rkt :11

(define input (input-load-lines "main.log"))

; 214M(VIRT)/101M(RSS) without open any file
(let loop()
  (sleep 5) ; Waiting here so that I can check it via top/ps

  (set! input empty) ; event not help with this line

  (loop))

Thanks

Hong

[Hong Yang]

Update with memory dump log attached.

1. With out (set! input empty), call (collect-garbage) doesn't help

2. Call (set! input empty) and (collect-garbage), memory reduce dramaticly.

; 214M(VIRT)/101M(RSS) without open any file
(let loop()
  (sleep 5)          ; Waiting here so that I can check it via top/ps

  (dump-memory-stats)
  (collect-garbage)
  (set! input empty)  ; Even not help with this line, it works after called (collect-garbage) explicity.
  (loop))

[Laurent]

Quick comment: of you don't need to load the whole file but want to parse it line by line, use `in-lines` which is memory-efficient.

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[Hong Yang]

Thanks Laurent, I tried (in-lines...), and yes, it's memory-efficient, but I still curious and concern why (port->lines ...) takes so many memory.

Best regards

Hong

[Sam Tobin-Hochstadt]

port->lines produces a list with all the lines in it. That list is what uses all the memory. Using in-lines avoids producing the whole list at once. 

Sam

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[jackh...@gmail.com]

I'm also guessing the jump from 600MB to 3GB is related to encodings. The file is probably UTF8/ASCII, and racket strings are a different encoding. I think they're one of the 32-bit encodings? So for ASCII text that alone would be a factor of four increase in memory usage.