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Re: file system storage engine


Hi Stewart,

I've updated my branch to fix the problems.
could you please do some review over my branch? It would be helpful.
the locking part still has some problems, when two sessions try to update
different rows,
shouldn't this be prevented by table lock?

the next step would be:
1. investigate how other storage engine, say blitzdb  handles the locking,
and learn something from it.
2. add support for tag files so that this engine handle read files like
/proc/meminfo directly.

On Tue, Jun 8, 2010 at 9:02 AM, Stewart Smith <stewart@xxxxxxxxxxxxxxxx>wrote:

> (CC'd drizzle-discuss in case anybody else has some thoughts too)
> On Mon, 07 Jun 2010 18:58:56 +0800, Zimin <ziminq@xxxxxxxxx> wrote:
> >   lp:~ziminq/drizzle/filesystem-storage-engine
> A few things:
> - it looks like you haven't merged from trunk in a while, you should try
> to keep rather up to date with trunk.
> - in ha_filesystem::open
>  - the table message is already loaded by the upper layer, so you can
>    access it through table->share (see table_share.h)
>  - It looks as though you're not trying to open the actual file there?
>  - you should probably try to open the file there and report back
>  errors
> - in doStartTableScan
>  - instead of using cerr for errors, use something like
>  push_warning_printf:
>  (for example, from embedded_innodb):
>  if (innodb_err != DB_SUCCESS)
>  {
>    push_warning_printf(&session, DRIZZLE_ERROR::WARN_LEVEL_ERROR,
>                        ER_CANT_CREATE_TABLE,
>                        _("Cannot create table %s. InnoDB Error %d (%s)\n"),
>                        innodb_table_name.c_str(), innodb_err,
> ib_strerror(innodb_err));
>    return HA_ERR_GENERIC;
>  }
> - in rnd_next()
>  - Don't use drizzled::String, instead use std::string.
>  - have so you have a row separator as well as a column separator
>    e.g. a CSV file has ROW_SEPARATOR='\n', COLUMN_SEPARATOR=','
>  - you should set each field not null using Field instead of using
>    memset.
> - position() and rnd_pos()
>  - you will need to implement these (check out my rnd_pos test for
>    embedded_innodb).
>  - they should be pretty easy. store the position in the file, seek to
>    it.
>  - you will need to set ref_length in ::open (see embedded_innodb for
> example)
> - info()
>  - you'll need some things here, but shouldn't be hard.
> - locking
>  - you probably want to write out the locking strategy.
>  - possible have options? fcntl locks?
>  - you have a table share (that isn't used), so the locking doesn't
>    work :)
>  - keep in mind that Drizzle is very much about removing horrible table
>    level locks, so this is the responsibility of the engine.
> - insert/update row
>  - you need to operate on the buffer you're given. this means using
>    move_field_offset and that awful API (i've written a blog post on
>    this recently)
> > I would like to know whether such approach is OK or not.
> > and I use iostream file operation, is it ok? I know that getline() is
> > slow on big files.
> In theory it should be okay - but what about the case where rows are not
> delimited by newlines?
> > to delete and update a line, I used a temp file and rename the temp file
> > to the original one, it's kind of ugly.
> I think it'd be great if you also:
> - added more blueprints for each feature
> - targeted these blueprints for a series (Dexter)
> - targeted these blueprints for milestones (i.e. dates where you aim to
> have code with that functionality merged into the main tree)
> I do really like that there are tests there too!
> great work so far, hopefully the above helps!
> --
> Stewart Smith

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