Re: Cluster Limitation questions...

[Mikael Ronström]

Hi Andrew,

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

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

Correct.

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

It is also to simplify internal implementation to avoid tuples 
spreading over several pages and it is also to avoid wasting memory in 
pages (in worst case
almost half the DataMemory could be wasted if allowing full page sized 
tuples. TEXT and BLOB only a store a prefix in the real table so you 
are correct
in this assumption. The large part of the TEXT and BLOB record is 
stored in a number of records in a separate BLOB table.

> (I'm starting to have scary thoughts about some tables that currently 
> have indexed TEXT cols.. to convert to a different format would bump 
> them over the 8k limit per row, but to leave as is, would affect 
> indexing)
>
> oh fun :)
>
> the foreign Key construct is ignored:  can I stll call cascades thu a 
> query on a  table with a PK, and see the affects cascade thru the FK 
> 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 
yet some time. Eventually it will come to other MySQL handlers as well.

Rgrds Mikael

> thanks in advance...
>
> a
>
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Mikael Ronström, Senior Software Architect
MySQL AB, www.mysql.com

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