From: Date: February 1 2005 8:54am
Subject: Re: Cluster Limitation questions...
List-Archive: http://lists.mysql.com/cluster/1442
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Hi Andrew,

2005-01-31 kl. 17.33 skrev Andrew Poodle:

> I'm developing a proof of concept cluster, and would like some help=20
> and/or clarification of some of the points I've come across in the=20
> limitations.
>
> No Text Indexes:  Does this mean that columns with datatype "text"=20
> cannot be indexed?
>

Correct.

> Can someone clarify what is meant by prefix indexes?  Is this where=20
> only one of several indexed columns in a table is intended to be used?
>

If you have a BLOB (or TEXT) field, then you can define an index on the=20=

first 20 bytes of the BLOB (as an example), thus an index on a prefix
of the BLOB.

> The 8 k row limit, I recognise this is probably to keep down traffic=20=

> between nodes..  am I right in thinking if a field is changed to a=20
> TEXT or BLOB datatype, then those records aren't affected by the 8k=20
> limit? Is this 8k limit the actual data size of the row contents?
>

It is also to simplify internal implementation to avoid tuples=20
spreading over several pages and it is also to avoid wasting memory in=20=

pages (in worst case
almost half the DataMemory could be wasted if allowing full page sized=20=

tuples. TEXT and BLOB only a store a prefix in the real table so you=20
are correct
in this assumption. The large part of the TEXT and BLOB record is=20
stored in a number of records in a separate BLOB table.

> (I'm starting to have scary thoughts about some tables that currently=20=

> have indexed TEXT cols.. to convert to a different format would bump=20=

> them over the 8k limit per row, but to leave as is, would affect=20
> indexing)
>
> oh fun :)
>
> the foreign Key construct is ignored:  can I stll call cascades thu a=20=

> query on a  table with a PK, and see the affects cascade thru the FK=20=

> children, either delete or set to null whatever..
>
> I'd like to do this at db level and no application layer.
>

Sorry, foreign key is only supported in InnoDB and will remain so for=20
yet some time. Eventually it will come to other MySQL handlers as well.

Rgrds Mikael

> thanks in advance...
>
> a
>
> --=20
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>
>
Mikael Ronstr=F6m, Senior Software Architect
MySQL AB, www.mysql.com

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