----- Alkuperäinen viesti -----
Lähettäjä: "Gary Richardson" <gary.richardson@stripped>
Vastaanottaja: "Heikki Tuuri" <heikki.tuuri@stripped>
Lähetetty: Thursday, October 21, 2004 4:49 AM
Aihe: Re: Char to Varchar on Innodb
> I'm not too worried about it myself, but I can see how less magic on a
> database server is better.
> Without actually trying it, if I mix CHAR's and VARCHAR's in a table,
> does SHOW CREATE TABLE reflect the internal conversion?
> If you wanted to reduce fragmentation in an Innodb table, wouldn't all
> the CHAR fields need to be left-packed? For example, you'd still get
if the field to be UPDATEd is fixed size, then an UPDATE does not cause
fragmentation. That is what I meant.
> fragmentation if your columns went CHAR, VARCHAR, CHAR. I guess that
> is unless the engine underneath did this automagically.
InnoDB - transactions, row level locking, and foreign keys for MySQL
InnoDB Hot Backup - a hot backup tool for InnoDB which also backs up MyISAM
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> On Wed, 20 Oct 2004 11:29:30 +0300, Heikki Tuuri
> <heikki.tuuri@stripped> wrote:
> > Gary,
> > those 'silent column specification changes' affect all table types. That
> > feature has caused lots of user questions over years. It is in the TODO
> > remove that feature from MySQL, because it is not standards compliant.
> > InnoDB, a reason to use a CHAR column in some cases is to reduce
> > fragmentation if there are lots of updates to that column. A CHAR column
> > takes a fixed space. Silent column specification changes in many cases
> > defeat this optimization which would otherwise be available to users.
> > Best regards,
> > Heikki Tuuri
> > Innobase Oy
> > Foreign keys, transactions, and row level locking for MySQL
> > InnoDB Hot Backup - a hot backup tool for InnoDB which also backs up
> > tables
> > http://www.innodb.com/order.php
> > Order MySQL technical support from https://order.mysql.com/
> > ....................
> > Hey,
> > From http://dev.mysql.com/doc/mysql/en/Silent_column_changes.html:
> > <snip>
> > If any column in a table has a variable length, the entire row becomes
> > variable-length as a result. Therefore, if a table contains any
> > variable-length columns (VARCHAR, TEXT, or BLOB), all CHAR columns
> > longer than three characters are changed to VARCHAR columns. This
> > doesn't affect how you use the columns in any way; in MySQL, VARCHAR
> > is just a different way to store characters. MySQL performs this
> > conversion because it saves space and makes table operations faster.
> > See section 15 MySQL Storage Engines and Table Types.
> > </snip>
> > Does this affect all table types? I'm curious if this is happening on
> > my InnoDB tables as well. No problems, just curiosity..
> > Thanks.
> > --
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