What  used  so  many  spaces  in  PostgreSQL  data  folder?

Hello,

i installed Psql-7.1.3 on my RedHat6.2 server in /usr/loc
al/pgsql,after i create a database,there would be a subfolde
r created in /usr/local/pgsql/data/base,where stored data of
this database.
today,i found that the usage of space increased more 200
MB,it caused by some big files about 200 or 300 MB created,
for examples,the database folder named "6302683", part of all files,including some big files are listed below:

-rw------- 1 postgres postgres 16384 Jul 31 10:38 6302776
-rw------- 1 postgres postgres 8192 Jul 31 10:38 6302779
-rw------- 1 postgres postgres 34996224 Aug 1 10:01 6302790
-rw------- 1 postgres postgres 243318784 Aug 1 09:59 6302824
-rw------- 1 postgres postgres 4104192 Aug 1 09:59 6302836
-rw------- 1 postgres postgres 950272 Aug 1 10:01 6302839
-rw------- 1 postgres postgres 8192 Jul 31 13:29 6302842
-rw------- 1 postgres postgres 1245184 Jul 31 13:31 6302853

i don't kown why this happened.i am sure that this is not
caused by adding normal data into my database by clients.
What's the problem & How to solve it ??
(BTW,i remembered that when i read docs of PostgreSQL Admin
or User Guide,one line suggested that i should create sth in
Crond daemon to "clean" sth EVERYDAY or EVERY HOUR,by i could not find it exactly,maybe related with my question...)

Peter

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