some error messages in postgeslog

I use PostgreSQL 8.0.0

it seems that the disk was close to full,

i executed a program (in C++) which opens a connection to Postgres using PQConnectdb.

and then it reads from a particluar table, and simply displays the values on the console.

after doing that it will close the connection using PQfinish

and thats when these error messages come....

<2006-04-05 17:10:47 CDT%idle>LOG: disconnection: session time: 0:00:00.00 user=sdc database=dbexpress host=[local] port=
<2006-04-05 17:10:47 CDT%idle>LOG: disconnection: session time: 7:41:26.70 user=sdc database=dbexpress host=[local] port=
<2006-04-05 17:10:47 CDT%>ERROR: could not access status of transaction 0
<2006-04-05 17:10:47 CDT%>DETAIL: could not write to file "/export/home1/sdc_image_pool/dbx/pg_clog/0001" at offset 40960:
No space left on device
<2006-04-05 17:10:48 CDT%>LOG: could not close temporary statistics file "/export/home1/sdc_image_pool/dbx/global/pgstat.tm
p.24783": No space left on device
<2006-04-05 17:10:49 CDT%>ERROR: could not access status of transaction 0
<2006-04-05 17:10:49 CDT%>DETAIL: could not write to file "/export/home1/sdc_image_pool/dbx/pg_clog/0001" at offset 40960:
No space left on device
<2006-04-05 17:10:50 CDT%>ERROR: could not access status of transaction 0
<2006-04-05 17:10:50 CDT%>DETAIL: could not write to file "/export/home1/sdc_image_pool/dbx/pg_clog/0001" at offset 40960:
No space left on device

is it true that for starting a connection to postgres read a table and then closing connection disk space will be needed.

Is it because of this reason these error messages are coming?



i have another question i have also noticed this error message in the postgres log, what are its implications and what happened that this error message came
:
2006-04-05 09:22:08 CDT%>LOG: received fast shutdown request
<2006-04-05 09:22:08 CDT%>LOG: aborting any active transactions
<2006-04-05 09:22:08 CDT%>LOG: checkpoints are occurring too frequently (16 seconds apart)
<2006-04-05 09:22:08 CDT%>HINT: Consider increasing the configuration parameter "checkpoint_segments".


Thanks,
regards
Surabhi