Question

Is there/has somebody any comparison, personal experience, or guideline when to use the text type instead of a large varchar in MySQL?

While most of the entries in my database will be less than 1000 characters, some might take up to 4000 characters or more. What is the limiting length of varchar which makes text a better variant?

I do not need to index those fields.

Answer 1

I don’t have personal experience, but this guy does:

VARCHAR vs. TEXT – some performance numbers

Quick answer: varchar was a good bit faster.

Edit – no, it wasn’t. He was indexing them differently – he had a full index on the varchar (255 chars) but a 255-char prefix index on the text. When he removed that, they performed more or less the same.

Later in the thread is this interesting tidbit:

When a tmp table is needed for a
SELECT, the first choice is to use
MEMORY, which will be RAM-only, hence
probably noticeably faster. (Second
choice is MyISAM.) However, TEXT and
BLOB are not allowed in MEMORY, so it
can’t use it. (There are other reasons
why it might skip MEMORY.)

Edit 2 – some more relevant info, this time comparing the way different indices deal with the various types.

MyISAM puts TEXT and BLOB ‘inline’. If
you are searching a table (range scan
/ table scan), you are ‘stepping over
those cow paddies’ — costly for disk
I/O. That is, the existence of the
inline blob hurts performance in this
case.

InnoDB puts only 767 bytes of a TEXT
or BLOB inline, the rest goes into
some other block. This is a compromise
that sometimes helps, sometimes hurts
performance.

Something else (Maria? Falcon? InnoDB
plugin?) puts TEXTs and BLOBs entirely
elsewhere. This would make a
noticeable difference in performance
when compared to VARCHAR. Sometimes
TEXT would be faster (eg, range scan
that does not need the blob);
sometimes the VARCHAR would be faster
(eg, if you need to look at it and/or
return it).