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From:Sergei Golubchik Date:February 20 2006 6:45pm
Subject:Re: MYI ... Basedata ...
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Hi!

On Feb 19, Hagen H?pfner wrote:
> >> ------------------------------------------------------------
> >>   mi_int4store(ptr,base->pack_reclength);        ptr +=4;
> >> Is this the average for a packed record? If so, how is it computed?
> >> If I do not pack the data file, then pack_reclength is equal to
> >> reclength, isn't it?
> >
> > How it's computed - see mi_create.c.
> > It's equal if there's no live checksum, and pack_reclength
> > is not less than rec_reflength.
> >
> > Not the average, it's basically the reclength above without
> > rec_reflength/checksum correction.
> Hm, I looked at the source code and found:
> 
>   share.base.reclength=real_reclength;
>   share.base.pack_reclength=reclength+ test(options & HA_OPTION_CHECKSUM);
> 
> For me this looks like that pack_reclength is the reclength WITH
> corrections.

Yes, sorry. It's reclength WITH rec_reflength/checksum correction.

> However, as longer as I think about the MyISAM driver as more obvious
> is the question, what "pack" means exactly. Does it really mean
> compression or only the way of representing (uncompressed) the data in
> main memory?

No, it does not mean compression. It mainly refers to stripping
endspaces from VARCHAR. Check _mi_rec_pack().
 
Regards,
Sergei

-- 
   __  ___     ___ ____  __
  /  |/  /_ __/ __/ __ \/ /   Sergei Golubchik <serg@stripped>
 / /|_/ / // /\ \/ /_/ / /__  MySQL AB, Senior Software Developer
/_/  /_/\_, /___/\___\_\___/  Kerpen, Germany
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Thread
MYI ... Basedata ...Hagen Höpfner19 Dec
  • Re: MYI ... Basedata ...Sergei Golubchik19 Dec
    • Re: MYI ... Basedata ...Hagen Höpfner3 Feb
      • Re: MYI ... Basedata ...Sergei Golubchik7 Feb
    • Re: MYI ... Basedata ...Hagen Höpfner20 Feb
      • Re: MYI ... Basedata ...Sergei Golubchik20 Feb
        • Packed Data in MyISAMHagen Höpfner23 Feb
          • Re: Packed Data in MyISAMSergei Golubchik23 Feb
            • Re: Packed Data in MyISAMHagen Höpfner23 Feb
              • Re: Packed Data in MyISAMSergei Golubchik24 Feb