On Apr 23, 2007, at 7:16 AM, Merlin Moncure wrote:
On 4/20/07, chrisj <chrisj.wood@xxxxxxxxxxxx> wrote:
I have a table that contains a column for keywords that I expect
to become
quite large and will be used for web searches. I will either
index the
column or come up with a simple hashing algorithm add the hash key
to the
table and index that column.
I am thinking the max length in the keyword column I need to
support is 30,
but the average would be less than10
Any suggestions on whether to use char(30), varchar(30) or text,
would be
appreciated. I am looking for the best performance option, not
necessarily
the most economical on disk.
Don't use char...it pads out the string to the length always. It
also has no real advantage over varchar in any practical situation.
Think of varchar as text with a maximum length...its no faster or
slower but the database will throw out entries based on length (which
can be good or a bad thing)...in this case, text feels better.
AIUI, char, varchar and text all store their data in *exactly* the
same way in the database; char only pads data on output, and in the
actual tables it still contains the regular varlena header. The only
reason I've ever used char in other databases is to save the overhead
of the variable-length information, so I recommend to people to just
steer clear of char in PostgreSQL.
--
Jim Nasby jim@xxxxxxxxx
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
