Slow Query / Check Point Segments

Hii am experience slow queries when i run some functions. I noticed the following entries in my server log.
>From this, can anyone tell me if I need to change some config parmeters?
System has 18GB Memoryshared_buffers = 4GB # min 128kBtemp_buffers = 32MB # min 800kBmax_prepared_transactions = 100 # zero disables the featurework_mem = 256MB # min 64kBmaintenance_work_mem = 1GB # min 1MBwal_buffers = 1024kB # min 32kBcheckpoint_segments = 32 # in logfile segments, min 1, 16MB eachcheckpoint_timeout = 30min # range 30s-1h

2010-01-22 12:18:11 JSTLOG: checkpoint complete: wrote 52037 buffers (9.9%); 0 transaction log file(s) added, 0 removed, 0 recycled; write=67.441 s, sync=0.000 s, total=67.453 s2010-01-22 12:21:48 JSTLOG: checkpoint complete: wrote 83874 buffers (16.0%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=138.040 s, sync=0.000 s, total=138.063 s2010-01-22 12:23:32 JSTLOG: checkpoint complete: wrote 82856 buffers (15.8%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=18.740 s, sync=0.000 s, total=18.783 s2010-01-22 12:24:26 JSTLOG: checkpoint complete: wrote 75145 buffers (14.3%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=12.129 s, sync=0.000 s, total=12.132 s2010-01-22 12:25:30 JSTLOG: checkpoint complete: wrote 82108 buffers (15.7%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=10.619 s, sync=0.000 s, total=10.621 s2010-01-22 12:28:03 JSTLOG: checkpoint complete: wrote 87349 buffers (16.7%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=82.190 s, sync=0.000 s, total=82.192 s2010-01-22 12:30:02 JSTLOG: checkpoint complete: wrote 80797 buffers (15.4%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=78.198 s, sync=0.000 s, total=78.201 s2010-01-22 12:32:03 JSTLOG: checkpoint complete: wrote 81365 buffers (15.5%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=75.968 s, sync=0.000 s, total=75.971 s2010-01-22 12:33:32 JSTLOG: checkpoint complete: wrote 98258 buffers (18.7%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=52.156 s, sync=0.000 s, total=52.159 s2010-01-22 12:34:51 JSTLOG: checkpoint complete: wrote 80089 buffers (15.3%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=53.385 s, sync=0.000 s, total=53.387 s2010-01-22 12:36:08 JSTLOG: checkpoint complete: wrote 80819 buffers (15.4%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=51.476 s, sync=0.000 s, total=51.478 s2010-01-22 13:01:54 JSTLOG: checkpoint complete: wrote 4892 buffers (0.9%); 0 transaction log file(s) added, 0 removed, 32 recycled; write=494.868 s, sync=0.000 s, total=494.982 s
Thanks for any adviceAlex
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