Re: [Mysqlfs-general] Discovered a bug?

[Lester H. <hig...@10...>]

The patch is definately incomplete in the corner cases you described.
I'll follow this email up with a forward of the original patch, just to
you.

--
Lester


On Fri, 23 Mar 2007, Michal Ludvig wrote:

> Hi Lester,
>
> that's right, I have already found it in archives on SourceForge  [*].
> But the patch isn't quite readable there. Could you resend it please?
>
> BTW Have you dealt with mid-file updates in your patch? For instance
> write 8kB file and then rewrite 2kB of data at offset 3kB, i.e. touching
> two 4kB blocks with one update. And how about truncate()? From what I
> could read from the archive the patch is somewhat incomplete in these
> "corner" cases.
>
> Michal
>
> [*]
> https://sourceforge.net/mailarchive/forum.php?thread_id=30626251&forum_id=50318
>
> Lester Hightower wrote:
> > Michal,
> >
> > On Mon, 25 Sep 2006 at 13:29:17 EDT, I submitted a patch for mysqlfs-0.2,
> > to mys...@li..., which does exactly what you
> > describe below, and under the subject "Patch to mysqlfs-0.2 to break file
> > data into records of 4k chunks."  You can likely save yourself some time
> > by referring to that patch.  A positive side-effect that I noted in that
> > email is, "My testing of this code shows better than a 10-fold increase in
> > write speed, and that improvement is more pronounced on larger files.  It
> > also shows a 3-fold increase in read speed."
> >
> > If you have trouble finding that email, drop me a separate email and I'll
> > send it to you again.
> >
> > Sincerely,
> >
> > --
> > Lester Hightower
> >
> >
> > On Fri, 23 Mar 2007, Michal Ludvig wrote:
> >
> >> Stef Bon wrote:
> >>
> >>> But I ran into troubles when I wanted to try it. The description you'll find
> >>> at:
> >>>
> >>> https://sourceforge.net/tracker/index.php?func=detail&aid=1681567&group_id=129981&atid=716425
> >> As I suspected this happens to files larger than 1MB. I have debugged
> >> the behaviour and the problem is:
> >> - the content of a file is held in a "LONGBLOB" field in the DB
> >> - as the data come in 4kB chunks, longblob gets appended the current
> >>   chunk
> >> - this is done with "UPDATE ... SET data=CONCAT(data, <new chunk>)" like
> >>   query
> >> - Now when the current length of "data" plus the length of "new chunk"
> >>   goes over 1MB mysql fails with:
> >>   "Result of concat() was larger than max_allowed_packet (1048576) -
> >>   truncated" and 'data' is set to NULL.
> >>
> >> So this is in brief the problem. I'm not sure how to solve it though.
> >>
> >> The best approach seems to be splitting the data field into logical
> >> "blocks" of, say, 4kB. Then, instead of having the file contents in a
> >> single row in a single field in the database it'll be in a number of
> >> related rows. It will complicate the write()-call logic a little bit,
> >> but it should both improve write speed and fix this problem. IIRC this
> >> has been proposed on the list or maybe on SF tracker some months ago but
> >> I haven't followed up on that. Shame on me.
> >>
> >> I hope to have a new release ready sometime next week. And if not, well
> >> ... then it will be later ;-)
> >>
> >> Michal
> >
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