Hey folks,
I am working on a rather small, simple database. I'm running 7.3.5 on
an OpenBSD 3.5-STABLE machine (1.3GHz, 512M RAM, IDE drive using UDMA-5).
I am parsing and storing emails, so I have a lot of character string
data to worry about. In one particular table, I have 26 columns of type
varchar, with widths of 24-8192 characters. This is the table that is
giving me some pretty severe performance problems.
For example, many of the statistics I run against these emails is a
simple count(), whether it be on a column or *. Right now, counting the
rows takes in excess of 3.5 seconds. OK, that's pretty slow. However,
there are only --> 24,000 <-- rows in this table! I could see it taking
a long time if I had 500,000 rows, or a million, but 24,000?
Now, I am not an expert with database design whatsoever, so I fully
admit that having a table with 26 varchar columns (along with a handful
of other fixed-width columns) probably isn't the brightest design. :)
So, I went ahead and created an exact copy of this table, with the
exception of creating all character columns as type char(), not varchar().
I was pondering if making PostgreSQL worry about the varying lengths
by using varchar was the problem...
And sure enough, counting the rows on the new table takes around
148ms. That's a pretty big difference from 3600ms. And no, 3.6 seconds
doesn't sound like much, until you have several operations on the same
table to draw a single web page, and suddenly the page takes 20s to
load. :(
So, my question for the gurus: is using varchars THAT detrimental?
Or am I just going way way overboard by having so _many_ in a single
table? Or am I an idiot? (honest question - I'm armpit-deep in learning
mode here) I'm also curious to know if I've crossed some invisible
line with the number of columns/width of rows that makes performance
degrade rapidly.
If further info is needed, please ask - I just didn't want to spam
the list with further table definitions and explain analyze output if
it wasn't needed.
Benny
--
"Oh, the Jedis are going to feel this one!" -- Professor Farnsworth,
"Futurama"
