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Re: InstantDB: Read only binary column ?


Mathew

You're right in just about everything you say. Let me try to clarify the
situation a little. VARCHAR fields in InstantDB are, as you say, fixed
length. So a VARCHAR (65535) will always create a field which holds exactly
65535 chars in each row. InstantDB holds the length so that the actual
string stored or returned is variable length, but the space reserved on disk
is always the maximum size defined by the field.

A binary field, such as TEXT fields is true variable length. The amount of
disk space taken up by a variable length field will vary with the size of
the field in each row. When creating a results set which contains a binary
field InstantDB needs an underlying writable file to hold the contents of
the field in the results set. If you know for certain that such a writable
file system exists (say a ramdisk or a writable portion of the user's hard
drive) then you can direct the tmpPath to that location. If you don't know
for certain that such a writable file system will be present then, for now
at least, you won't be able to use binary fields.

Regards

Pete

--

Peter Hearty                         peter.hearty@lutris.com
Lutris Technologies (UK)        http://www.lutris.com
----- Original Message -----
From: "Matthew Davidson" <matthew.davidson@scholarone.com>
To: <instantdb@enhydra.org>
Sent: Monday, September 11, 2000 4:38 AM
Subject: InstantDB: Read only binary column ?


> Hi, I was considering using InstantDB for a project, but came across
> something that seems problematic. We're rewriting a website, originally
> written in PHP, to Java, in order to place on a CD. All the necessaary
> data will be flattened into a single database, and accessed locally,
> instead of over the net.
>
> The problem seems to be that the documentation states in readonly mode,
> InstantDB cannot have readonly binary fields, which our database
> currently uses. Now, the documentation isn't too clear on this point;
> can it have binary fields, but not enforce the readonly aspect? It seems
> that you can specify a tmp location for InstantDB to use ("e.g. Set
> tmpPath=$user.home in the database properties file"), so can it use them
> after all?
>
> If I can't use a readonly binary column, I think I can get away with a
> large varchar field, since the only reason we used a binary field
> (MySQL's TEXT) was that MySQL didn't support varchar fields larger than
> 255 chars. However, there was some email exchange between a Peter Hearty
> and a Markus Strickler about the maximum length of the rows:
>
> > All of InstantDB's table rows are fixed length, unless you use one of
the
> > BINARY types. If you allocate a 65535 varchar field then you'll be
> > allocating a fixed size 65535*2 ('cos it's unicode) field in every row.
If
> > you want genuine variable length character fields, use the TEXT type.
> >
> > Regards
> > Peter Hearty
> > Lutris Technologies (UK)
>
> What exactly is the maximum length of a row in InstantDB? I don't think
> I would cross it with this project, since the largest number of chars
> held in the field in question is only a few thousand, but I might cross
> it later, so I wanted to know.
>
> Thanks In Advance,
> Matthew
> ScholarOne
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