Re: Filesystem performance overheads?

From: Information (info_at_mcobject.com)
Date: 06/14/05

  • Next message: Rick Jones: "Re: problem about CPU load testing on PPC750" 
    Date: Mon, 13 Jun 2005 15:46:03 -0700

    For another take on this topic, you might have a look at this article that
    compares a database in a ramdisk versus an in-memory database, both on Linux
    systems.

    In-Memory Database Systems

    Linux Journal, September 1, 2002

    http://www.linuxjournal.com/article.php?sid=6133

    Or the proprietary version:
    http://www.mcobject.com/downloads/memorybenchmark.pdf

    "Gene S. Berkowitz" <first.last@comcast.net> wrote in message
    news:MPG.1cf093d3c25a235e9897dc@news.comcast.giganews.com...
    > In article <4283b402$1@news.tulsaconnect.com>, johnnyb@eskimo.com
    > says...
    >> > Is anyone aware of studies that have been done to measure the
    >> > performance overheads that result from using a filesystem? We want to
    >> > know the performance loss that we would suffer using a filesystem like
    >> > FAT16 on a ramdisk versus using the memory as it is (raw reads and
    >> > writes to memory, without considering it as a ramdisk with a file
    >> > system).
    >>
    >> It may be "small" but not "miniscule". For every access you would have
    >> to do a context switch and the kernel would have to run just to read
    >> data, as opposed to just being able to read it with one instruction and
    >> no context switch.
    >
    > FAT16 (and variants) require walking the FAT chain whenever it is
    > necessary to append, truncate, or seek in a file. Depending on
    > cluster size and file size, that can be quite significant, and result in
    > quite noticeable delays. Additionally, depending on the implementation,
    > it's necessary to only allow one process access to the FAT at a time, in
    > order to prevent corruption.
    >
    > --Gene

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