Initially shared_buffers were set to 1000 (8MB). Then, we moved all apps but the database server off the box. Raised shared_buffers to 2000 (16MB). Modest improvement in some frequent repeated queries. Raised shared_buffers to 16000 (128MB). DB server dropped to a CRAWL.
Versions below 8.1 normally don't do well with high shared_buffers. 8.1 would do much better. If you dropped that to more like 6k you would probably continue to see increase over 2k.
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